Frequently Asked Questions page
FAQ page
- All
- Battery Drain Diagnosis
- Diagnostics & Fault Finding
- General Questions
- Mobile Service
- Module replacement
- Programming & Coding
- Vehicles Covered
Yes used modules can be fitted to the vehicle. This is sometimes the only way to get a replacement module as they are sometimes not available to buy new from the main dealers.
This makes it cheaper to replace the part, but is sometimes a bit “hit and miss” as to whether the new used module is a “good” module, until we get to programming the module, it is difficult to know if we have a good used module to work on the car. It is totally possible to replace with a used module though, and it is a good route to go sometimes. The used modules are often sold as good working modules and it isn’t a con from the seller (often vehicle dismantlers yards), they usually respond quickly and send another out if there is an issue.
A vehicle control module is a small computer looking after a specific system in a vehicle (ABS, Airbags, Audio system etc etc etc).
Some newer vehicles have 40 to 50 control modules in the vehicle. They all talk to all the other modules on a CAN bus line (data line), and some vehicles have 3 to 4 different CAN bus lines (high speed for urgent signals, medium speen CAN bus, slow speed CAN bus line, and other data lines too, like LIN bus lines) Some alternators (device that charges the battery) has a LIN bus line attached so that the main engine computer knows what the alternator is doing (what voltage is it charging the battery at?, how many amps is the charging rate, temperature of the regulator (circuit that converts AC electric to DC for the battery), the ECU (engine computer) also monitors error codes and the general health and well being of the alternator). So modules are very important in modern cars. Without them the car won’t start at all, and a fault on one will create errors on the CAN bus line, so the othe modules know there is an issue.
If a module ever needs to be replaced, it will need to be programmed to work in the car. Sometimes the old modules existing data can be copied to the new (or new second hand) module. It won’t work – or be accepted in the system unless it is programmed. Depending on what module it is, depends on the data required. Usually the VIN number is essential (read this page to find out more about VIN numbers). If it is an immobiliser module, the existing keys have to be programmed in to it so that they work with the new module – or the car simply will refuse to accept the existing keys to lock / unlock or even start the car.
Yes, modern vehicles are often in need of some electrical fault finding. I work on new vehicles regularly, they have a lot more electronic systems packed in to them, so they have more to go wrong essentially. I try to stay away from fully electric vehicles, as I have most, if not all my experience from working on petrol or diesel engine vehicles.
Yes battery drains can be diagnosed on modern vehicles too, and they often have this fault sometime in their life because modern vehicles have so much more electronics on board. It isn’t uncommon to have 30 – 40 computer modules onboard, all with data lines linking them together so that all the systems in the car can communicate. This works well when the system works as it should, but when there is an issue with a module it can wake all the other modules up on the CAN network, so now instead of one module “awake”, all of them are communicating when the car is supposed to be “asleep”.
It takes anything from 10 minutes to nearly an hour for all modules to go to sleep when you lock the vehicle (depending on make / model of car and what spec it is). The car needs to have shut down with modules asleep to be able to start fault finding, so this part of it is time consuming, so for vehicles suffering from large battery drains, I often take them home to work on as I can be busy at home while waiting for the vehicle to go to sleep, then go and do some diagnostic work on the vehicle, and when it wakes up, I can go ins to the house to eat, boil the kettle, write invoices / do paperwork etc etc instead of standing next to the car waiting for it to enter sleep mode again.
Yes new batteries (like older bateeries) can still go flat. It usually takes more to drain a new battery, but if you leave the headlights on, or even just the interior light, depending on what length of time it is left on for without the engine running, the battery will drain. If you manage to start the car with a slightly drained battery, either take it for a drive so that the alternator puts some more charge back in to the battery, or put the battery on charge with a battery charger.
If a new battery doesn’t hold a charge, you likely have something draining the power from the battery (an interior light, an aftermarket dash cam or handsfree phone kit for example).
Any question about this, click here to go to our contact page, and send a message.
Yes I can replace the ABS module, but I wouldn’t choose to do it out on the street etc as some are buried deep in the engine bay and would be better to do this on a ramp so that it can be accessed from under the vehicle a lot easier.
Not usually, no, but I will need the vehicle keys (sometimes all existing keys – for example if it is an immobiliser issue). I also need to know the details about the fault you have with the car, and will also need to know who to hand the vehicle keys back to at the end of the job. It’s good to have someone to liaise with if the job takes a bit longer than expected – or if I need authorisation to get a replacement for a failed component that I’ve found, but essentially I can work on the vehicle whether you are around or not if I know the answers to a few questions beforehand.
This could be that the battery you have in your vehicle is failing and needs to be replaced, or you have a battery drain from a device, component or wiring fault within the vehicle.
These are common problems:
Have you got an aftermarket alarm system fitted? Or a dashcam? – These are commonly responsible for battery drains in cars.
Have you got a light buld in the boot of the car that stays on when you lock the vehicle? Or the interior courtesy lights not going out?
If any of the above doesn’t give you the result you need, then you could do with having a battery drain current check. This is a multimeter connected in series with the battery to check how much current the electrical system draws once the vehicle is “asleep”. Cars take anything from 10 minutes to an hour to go to sleep – depending on what make the vehicle is / how many modules it has / how new the car is.
Your car shouldn’t be using more that 50 milliamps when asleep. Most cars are 25 – 30 milliamps or below.
If the current draw is too much, then a voltage drop test in millivolts needs to be done across each fuse. This usually (but not always) shows what wiring circuit is requesting the extra power during “sleep”. Sometimes this doesn’t work when a module is awake and then wakes all other modules up on the network. A different approach is required when this is the case, and we either unplug different modules, or split the wiring circuits up to try and test half of it at a time, to eventually come to the answer of what is keeping the car awake. We’ve seen faulty instrument panels, faulty modules, radios that want to wake different circuits. It’s the more challenging side of battery drains when a device wakes up other devices during “sleep”.
Yes, a vehicle that doesn’t start is often due to an electrical fault.
These types of faults can include:
Earth problems (Bad engine earth strap, so the starter motor can’t get enough / or any current to work
Signal / communication issues between the ECU and a component (injectors, coil packs, other modules on the network etc)
Relay fault, so it doesn’t switch power on to a circuit (fuel pump, starter etc)
Fuse blown, so a wiring circuit has no power. This could be a critical circuit for the engine to start
Key immobiliser issue. We can test to see if the immobiliser recognises the key, and “sees” it in the ignition
Alarm immobiliser fault. Due to an issue inside the alarm system it may not be allowing the immobiliser to give the right signal to the ECU
Obviously the vehicle not starting could also be due to there not being any fuel in the vehicle, or the timing belt broken etc etc. These are clearly mechanical issues, but we can diagnose them and they can be fixed at a garage.
Good diagnosis is key to all of this. People have changed starter motors to find it didn’t fix the fault of a non start. Then they get a proper diagnostic check done on the vehicle and find this issue was somewhere else, and once fixed the car runs properly.
Yes. These can be interesting faults to diagnose as the CAN network is sensitive (it doesn’t want any interference witin it.
faulty wiring (broken, rubbed through, water ingress etc), noise that the CAN bus wires pick up electrically, malfunctioning CAN modules etc, bad / faulty or incorrect connections going to modules or the alternator etc.
Modern vehicles can have at least 3 CAN bus circuits and a LIN data circuit too, plus other data circuits (like fibre optic MOST circuits – for audio equipment in cars).
The CAN bus has 2 120 ohm resistors somewhere in the circuit to help smooth out the communication signals within the wiring for that circuit. When a wire becomes disconnected this changes the resistance in the wiring, and also breaks the communication to other modules beyond where the wire is broken. With cars like the Range Rover there can be 50 modules in the CAN bus networks making the fault finding all the more challenging.
Yes, these are often easier to work on in many ways. There are few to no modules, less wiring, sensors, connectors etc.
But it also means that often there is no diagnostic socket in the car for a fault code reader, but the faults are (usually) easier to find and repair.
Most faults I repair, but if it is more of a mechanical fault I ask for it to go to a garage for repair / replacement of the failed part.
I replace sensors, wiring, control modules, ECU’s etc, but if the fault is diagnosed to be injectors or camshaft timing etc etc I’m just not interested in doing the work. I have worked in garages for many years and done all these mechanical jobs since leaving school in 1987, but I’d rather focus on the electrical systems.
At the moment I cover all of Oxfordshire and surrounding areas. The larger places within Oxforshire are listed below:
Abingdon
Farringdon
Carterton
Wantage
Burford
Biscester
Witney
Banbury
Chipping Norton
Wallingford
But I do go further afield sometimes – to surrounding counties.
The reason I said at the start of this reply “At the moment” – I am in the process of relocating to Aberdeenshire in Scotland, so this wil change my work area drastically in a few months to come. No specific date is set for the move yet, as I’m waiting for the sale of the house to go through. I’ll update this page when I have more information.
Yes.
That is mainly all we offer. We come to you, diagnose and / or fix your car where it is.
On newer vehicles with a parasitic battery drain I do sometimes have them where I live as this makes the fault finding a lot easier.
Newer vehicles can take anything up to an hour to fully go to sleep. When tracing a battery drain it is important to put the vehicle to sleep to see what current draw we have on the battery, and then trace the fault. The problem with newer vehicles is that the modules in the car wake up if a fuse is unplugged and plugged back in, or if a door is opened or a light switched on – and then it’s back to waiting for it to go to sleep again.
So with all the time waiting for the car to sleep, it is often better for me to do this at home – as I can go inside the house and eat a meal, get a coffee, do some paperwork etc etc, while waiting for the vehicle to enter sleep mode again.
Otherwise I am at a customers house waiting and waiting for the vehicle to enter sleep mode – with nothing else I can do, so having the vehicle at my home helps a lot with this.
When out at a customers house we can do all things related to electrical fault finding. There isn’t a disadvantage in what we can do, but sometimes that means working in wet, windy conditions to get the job done.
Essentially YES.
I do prefer working on petrol or diesel engine vehicles. Things are a bit different on hybrid and electric cars.
But yes, even tractors, farm machinery, busses etc – I work on all of them.
A simple answer would be:
A car diagnostic check is a computerised assessment of a vehicle’s engine, components, and electronic systems, identifying faults by retrieving error codes from the car’s Computer (ECU) via a scanner. It detects issues in the engine, transmission, brakes, and emissions system, allowing technicians to diagnose malfunctions accurately before costly repairs are needed.
Just to read the fault codes, there is a diagnostics port / plug socket within most vehicles that allow a fault code reader / scanner to be connected to interact with the ECU (and all the other modules). This can take 15 – 20 minutes to download and read all the fault codes logged in the system.
But this is only the start of it, as the error codes displayed are rarely the actual failed component or reason for the issue. It is often an issue within the wiring harness somewhere else in the vehicle leading to or from a component listed within the fault code report, or a failed module that sends / receives a signal from the sensor that is listed in the report from the scanner. Often, no fault code is stored on the ECU, or the ones that are stored are sometimes irrelevant. This is where the real diagnosis starts. Keep a copy of the fault codes. Clear the codes from the history. Try to replicate the fault, then get down to investigating the area of concern.
It really needs investigation work and that is what diagnostics is all about. Tracing wiring faults can sometimes be time consuming and difficult to do as sometimes voltage back feeds (from other modules / devices) down the wire being traced, making the job more difficult.
An auto electrician investigates electrical faults in vehicles. This is in depth work, that most garages don’t want to get involved in because of the amount of time involved with some faults, and also the expense of buying specific test tools (like osciloscopes to see electrical waveforms), there is also a lot of training – and keeping up to date with newer modules (computers) in cars.
We look in to all aspects of the electrical issue within a vehicle – for example:
Wiring (in and out of the wiring loom)
Connectors that join the wiring together, or connect to sensors, modules etc
The pins within connectors – these can get worn, bent out of shape, water ingress etc
Relays, switches (mechanical & electronic), fuses etc
Test expected outputs from components
View waveform of voltage, current flow, CANbus (data lines)
Perform voltage drop tests
Load test wiring to check wiring integrity
Check inputs and outputs from modules to ensure it is working properly
Repair of broken wires – often by soldering them back together, then using heat shrink tubing to protect and seal that new joint
There are many other things we get involved in – to do with electrical testing within vehicles, but it is all to test and prove wiring circuits, modules, injectors etc etc.
We do this to ensure that the systems on the car are working as they should, but also find faults within a specific system. This way we can identify where the fault originates from and can then make an informed decision of how to rectify the fault to bring the system back to working properly again.
- All
- Battery Drain Diagnosis
- Diagnostics & Fault Finding
- General Questions
- Mobile Service
- Module replacement
- Programming & Coding
- Vehicles Covered
Yes used modules can be fitted to the vehicle. This is sometimes the only way to get a replacement module as they are sometimes not available to buy new from the main dealers.
This makes it cheaper to replace the part, but is sometimes a bit “hit and miss” as to whether the new used module is a “good” module, until we get to programming the module, it is difficult to know if we have a good used module to work on the car. It is totally possible to replace with a used module though, and it is a good route to go sometimes. The used modules are often sold as good working modules and it isn’t a con from the seller (often vehicle dismantlers yards), they usually respond quickly and send another out if there is an issue.
A vehicle control module is a small computer looking after a specific system in a vehicle (ABS, Airbags, Audio system etc etc etc).
Some newer vehicles have 40 to 50 control modules in the vehicle. They all talk to all the other modules on a CAN bus line (data line), and some vehicles have 3 to 4 different CAN bus lines (high speed for urgent signals, medium speen CAN bus, slow speed CAN bus line, and other data lines too, like LIN bus lines) Some alternators (device that charges the battery) has a LIN bus line attached so that the main engine computer knows what the alternator is doing (what voltage is it charging the battery at?, how many amps is the charging rate, temperature of the regulator (circuit that converts AC electric to DC for the battery), the ECU (engine computer) also monitors error codes and the general health and well being of the alternator). So modules are very important in modern cars. Without them the car won’t start at all, and a fault on one will create errors on the CAN bus line, so the othe modules know there is an issue.
If a module ever needs to be replaced, it will need to be programmed to work in the car. Sometimes the old modules existing data can be copied to the new (or new second hand) module. It won’t work – or be accepted in the system unless it is programmed. Depending on what module it is, depends on the data required. Usually the VIN number is essential (read this page to find out more about VIN numbers). If it is an immobiliser module, the existing keys have to be programmed in to it so that they work with the new module – or the car simply will refuse to accept the existing keys to lock / unlock or even start the car.
Yes, modern vehicles are often in need of some electrical fault finding. I work on new vehicles regularly, they have a lot more electronic systems packed in to them, so they have more to go wrong essentially. I try to stay away from fully electric vehicles, as I have most, if not all my experience from working on petrol or diesel engine vehicles.
Yes battery drains can be diagnosed on modern vehicles too, and they often have this fault sometime in their life because modern vehicles have so much more electronics on board. It isn’t uncommon to have 30 – 40 computer modules onboard, all with data lines linking them together so that all the systems in the car can communicate. This works well when the system works as it should, but when there is an issue with a module it can wake all the other modules up on the CAN network, so now instead of one module “awake”, all of them are communicating when the car is supposed to be “asleep”.
It takes anything from 10 minutes to nearly an hour for all modules to go to sleep when you lock the vehicle (depending on make / model of car and what spec it is). The car needs to have shut down with modules asleep to be able to start fault finding, so this part of it is time consuming, so for vehicles suffering from large battery drains, I often take them home to work on as I can be busy at home while waiting for the vehicle to go to sleep, then go and do some diagnostic work on the vehicle, and when it wakes up, I can go ins to the house to eat, boil the kettle, write invoices / do paperwork etc etc instead of standing next to the car waiting for it to enter sleep mode again.
Yes new batteries (like older bateeries) can still go flat. It usually takes more to drain a new battery, but if you leave the headlights on, or even just the interior light, depending on what length of time it is left on for without the engine running, the battery will drain. If you manage to start the car with a slightly drained battery, either take it for a drive so that the alternator puts some more charge back in to the battery, or put the battery on charge with a battery charger.
If a new battery doesn’t hold a charge, you likely have something draining the power from the battery (an interior light, an aftermarket dash cam or handsfree phone kit for example).
Any question about this, click here to go to our contact page, and send a message.
Yes I can replace the ABS module, but I wouldn’t choose to do it out on the street etc as some are buried deep in the engine bay and would be better to do this on a ramp so that it can be accessed from under the vehicle a lot easier.
Not usually, no, but I will need the vehicle keys (sometimes all existing keys – for example if it is an immobiliser issue). I also need to know the details about the fault you have with the car, and will also need to know who to hand the vehicle keys back to at the end of the job. It’s good to have someone to liaise with if the job takes a bit longer than expected – or if I need authorisation to get a replacement for a failed component that I’ve found, but essentially I can work on the vehicle whether you are around or not if I know the answers to a few questions beforehand.
This could be that the battery you have in your vehicle is failing and needs to be replaced, or you have a battery drain from a device, component or wiring fault within the vehicle.
These are common problems:
Have you got an aftermarket alarm system fitted? Or a dashcam? – These are commonly responsible for battery drains in cars.
Have you got a light buld in the boot of the car that stays on when you lock the vehicle? Or the interior courtesy lights not going out?
If any of the above doesn’t give you the result you need, then you could do with having a battery drain current check. This is a multimeter connected in series with the battery to check how much current the electrical system draws once the vehicle is “asleep”. Cars take anything from 10 minutes to an hour to go to sleep – depending on what make the vehicle is / how many modules it has / how new the car is.
Your car shouldn’t be using more that 50 milliamps when asleep. Most cars are 25 – 30 milliamps or below.
If the current draw is too much, then a voltage drop test in millivolts needs to be done across each fuse. This usually (but not always) shows what wiring circuit is requesting the extra power during “sleep”. Sometimes this doesn’t work when a module is awake and then wakes all other modules up on the network. A different approach is required when this is the case, and we either unplug different modules, or split the wiring circuits up to try and test half of it at a time, to eventually come to the answer of what is keeping the car awake. We’ve seen faulty instrument panels, faulty modules, radios that want to wake different circuits. It’s the more challenging side of battery drains when a device wakes up other devices during “sleep”.
Yes, a vehicle that doesn’t start is often due to an electrical fault.
These types of faults can include:
Earth problems (Bad engine earth strap, so the starter motor can’t get enough / or any current to work
Signal / communication issues between the ECU and a component (injectors, coil packs, other modules on the network etc)
Relay fault, so it doesn’t switch power on to a circuit (fuel pump, starter etc)
Fuse blown, so a wiring circuit has no power. This could be a critical circuit for the engine to start
Key immobiliser issue. We can test to see if the immobiliser recognises the key, and “sees” it in the ignition
Alarm immobiliser fault. Due to an issue inside the alarm system it may not be allowing the immobiliser to give the right signal to the ECU
Obviously the vehicle not starting could also be due to there not being any fuel in the vehicle, or the timing belt broken etc etc. These are clearly mechanical issues, but we can diagnose them and they can be fixed at a garage.
Good diagnosis is key to all of this. People have changed starter motors to find it didn’t fix the fault of a non start. Then they get a proper diagnostic check done on the vehicle and find this issue was somewhere else, and once fixed the car runs properly.
Yes. These can be interesting faults to diagnose as the CAN network is sensitive (it doesn’t want any interference witin it.
faulty wiring (broken, rubbed through, water ingress etc), noise that the CAN bus wires pick up electrically, malfunctioning CAN modules etc, bad / faulty or incorrect connections going to modules or the alternator etc.
Modern vehicles can have at least 3 CAN bus circuits and a LIN data circuit too, plus other data circuits (like fibre optic MOST circuits – for audio equipment in cars).
The CAN bus has 2 120 ohm resistors somewhere in the circuit to help smooth out the communication signals within the wiring for that circuit. When a wire becomes disconnected this changes the resistance in the wiring, and also breaks the communication to other modules beyond where the wire is broken. With cars like the Range Rover there can be 50 modules in the CAN bus networks making the fault finding all the more challenging.
Yes, these are often easier to work on in many ways. There are few to no modules, less wiring, sensors, connectors etc.
But it also means that often there is no diagnostic socket in the car for a fault code reader, but the faults are (usually) easier to find and repair.
Most faults I repair, but if it is more of a mechanical fault I ask for it to go to a garage for repair / replacement of the failed part.
I replace sensors, wiring, control modules, ECU’s etc, but if the fault is diagnosed to be injectors or camshaft timing etc etc I’m just not interested in doing the work. I have worked in garages for many years and done all these mechanical jobs since leaving school in 1987, but I’d rather focus on the electrical systems.
At the moment I cover all of Oxfordshire and surrounding areas. The larger places within Oxforshire are listed below:
Abingdon
Farringdon
Carterton
Wantage
Burford
Biscester
Witney
Banbury
Chipping Norton
Wallingford
But I do go further afield sometimes – to surrounding counties.
The reason I said at the start of this reply “At the moment” – I am in the process of relocating to Aberdeenshire in Scotland, so this wil change my work area drastically in a few months to come. No specific date is set for the move yet, as I’m waiting for the sale of the house to go through. I’ll update this page when I have more information.
Yes.
That is mainly all we offer. We come to you, diagnose and / or fix your car where it is.
On newer vehicles with a parasitic battery drain I do sometimes have them where I live as this makes the fault finding a lot easier.
Newer vehicles can take anything up to an hour to fully go to sleep. When tracing a battery drain it is important to put the vehicle to sleep to see what current draw we have on the battery, and then trace the fault. The problem with newer vehicles is that the modules in the car wake up if a fuse is unplugged and plugged back in, or if a door is opened or a light switched on – and then it’s back to waiting for it to go to sleep again.
So with all the time waiting for the car to sleep, it is often better for me to do this at home – as I can go inside the house and eat a meal, get a coffee, do some paperwork etc etc, while waiting for the vehicle to enter sleep mode again.
Otherwise I am at a customers house waiting and waiting for the vehicle to enter sleep mode – with nothing else I can do, so having the vehicle at my home helps a lot with this.
When out at a customers house we can do all things related to electrical fault finding. There isn’t a disadvantage in what we can do, but sometimes that means working in wet, windy conditions to get the job done.
Essentially YES.
I do prefer working on petrol or diesel engine vehicles. Things are a bit different on hybrid and electric cars.
But yes, even tractors, farm machinery, busses etc – I work on all of them.
A simple answer would be:
A car diagnostic check is a computerised assessment of a vehicle’s engine, components, and electronic systems, identifying faults by retrieving error codes from the car’s Computer (ECU) via a scanner. It detects issues in the engine, transmission, brakes, and emissions system, allowing technicians to diagnose malfunctions accurately before costly repairs are needed.
Just to read the fault codes, there is a diagnostics port / plug socket within most vehicles that allow a fault code reader / scanner to be connected to interact with the ECU (and all the other modules). This can take 15 – 20 minutes to download and read all the fault codes logged in the system.
But this is only the start of it, as the error codes displayed are rarely the actual failed component or reason for the issue. It is often an issue within the wiring harness somewhere else in the vehicle leading to or from a component listed within the fault code report, or a failed module that sends / receives a signal from the sensor that is listed in the report from the scanner. Often, no fault code is stored on the ECU, or the ones that are stored are sometimes irrelevant. This is where the real diagnosis starts. Keep a copy of the fault codes. Clear the codes from the history. Try to replicate the fault, then get down to investigating the area of concern.
It really needs investigation work and that is what diagnostics is all about. Tracing wiring faults can sometimes be time consuming and difficult to do as sometimes voltage back feeds (from other modules / devices) down the wire being traced, making the job more difficult.
An auto electrician investigates electrical faults in vehicles. This is in depth work, that most garages don’t want to get involved in because of the amount of time involved with some faults, and also the expense of buying specific test tools (like osciloscopes to see electrical waveforms), there is also a lot of training – and keeping up to date with newer modules (computers) in cars.
We look in to all aspects of the electrical issue within a vehicle – for example:
Wiring (in and out of the wiring loom)
Connectors that join the wiring together, or connect to sensors, modules etc
The pins within connectors – these can get worn, bent out of shape, water ingress etc
Relays, switches (mechanical & electronic), fuses etc
Test expected outputs from components
View waveform of voltage, current flow, CANbus (data lines)
Perform voltage drop tests
Load test wiring to check wiring integrity
Check inputs and outputs from modules to ensure it is working properly
Repair of broken wires – often by soldering them back together, then using heat shrink tubing to protect and seal that new joint
There are many other things we get involved in – to do with electrical testing within vehicles, but it is all to test and prove wiring circuits, modules, injectors etc etc.
We do this to ensure that the systems on the car are working as they should, but also find faults within a specific system. This way we can identify where the fault originates from and can then make an informed decision of how to rectify the fault to bring the system back to working properly again.