Possible to disgnose a modern petrol non starter at home ?
Discussion
billm said:
kambites said:
Mine cost less than five pounds and, coupled with a smart-phone or laptop, will do everything I want it to. Best tool I ever bought. 
What make/model is it ? That sounds like a good investmentthanks
http://www.ebay.co.uk/itm/Super-Mini-ELM327-v2-1-O...
combined with an Android app called "Torque".
thanks, that's like the setup my son bought to find the ABS error on his Clio. Unfortunately we think not all Renault codes are publicised so it didn't tell us anything, neither did the local garage analyser who said the same thing, and said we'd have to get a Renault dealer to diagnose it with theirs.
But he has used it on his motorbike and it works on that too
But he has used it on his motorbike and it works on that too
A cheap system like that will only read the basic emissions specific codes. You need something more for ABS/SRS/etc codes.
I just bought one of these to read an ABS fault code on my wifes Civic.
https://www.launchtech.co.uk/enthusiast-diagnostic...
I just bought one of these to read an ABS fault code on my wifes Civic.
https://www.launchtech.co.uk/enthusiast-diagnostic...
The off-the-shelf software with the cheap dongles will usually only display OBD fault codes; that's a limitation of the software not the dongle though so if you're willing to put the effort in to look up the commands and submit them manually, they will do anything. I've only used mine in this way once and it is a pain in the arse, but it does work.
For some manufacturers there is third-party software available to do everything, for example VAGCOM for Volkswagen group cars. It's not cheap, but I rather suspect most home users pirate it. I suppose the price is relatively high because it's pitched at independent garages rather than individuals.
For some manufacturers there is third-party software available to do everything, for example VAGCOM for Volkswagen group cars. It's not cheap, but I rather suspect most home users pirate it. I suppose the price is relatively high because it's pitched at independent garages rather than individuals.
Edited by kambites on Tuesday 17th March 08:33
billm said:
thanks, that's like the setup my son bought to find the ABS error on his Clio. Unfortunately we think not all Renault codes are publicised so it didn't tell us anything, neither did the local garage analyser who said the same thing, and said we'd have to get a Renault dealer to diagnose it with theirs.
Yep, AFAIK you can't get an aftermarket code reader for Renault resulting in having to take it to the main stealers.I do like this thread, but am slightly worried by the mixture of facts and opinions.
Yes an engine still needs fuel, compression, spark. But once you found you have compression, it can be very difficult to find out why you don't have either spark or fuel or both. The most important thing to know is the facts about the particular car you are working on. Someone earlier said crank sensor is often the fault. This is true. But for instance a new Mercedes will still start and run using a reading from the camshaft sensor. But would run flat with the EML on.
What you really shouldn't do as instructed above is start throwing money at it, by replacing the cheapest parts first. A set of plugs will never be the reason a new car does not start. The chance of 4, 6, 8 or however many plugs your engine has failing all at once is almost impossible. The same can be said for individual coil packs. Yes they often go wrong, but that would just create a misfire.
Something like a misfire can still be diagnosed easily. Disconnect the coil packs one by one. When you unplug one and idle doesn't get even more lumpy, that's the cylinder at fault. But remember you still don't know if it's the plug, coil, injector, wiring loom or the control unit. Swap the coil with another. Try again.
Using basic unplugging and swapping technics lots can be diagnosed. But I would always recommend the fault codes are read. Then take those with a pinch of salt to.
Fault code says the upstream O2 sensor is faulty, so we replace it right? But what if it the air mass meter that has gone out of calibration. It is still working so the control unit doesn't see a fault. But it's richening up the mixture slightly which causes the O2 sensor to appear faulty. Or it could be a MAP sensor, or a knock sensor, leaking injectors, poor quality fuel, incorrect fuel, chafed or chewed through wiring, incorrect coding, inlet port shut off flaps stuck, or a seized EGR valve. The list goes on and on and is different for different brands and models.
Basically good modern diagnosis is still done using old fashioned techniques but using a computer to assist you. Most of the time a display of "actual values" is much more use than just a fault code. But most cheapo scanners won't do them or if they do, they don't give you the tolerances. It's fine to know a sensor is giving a signal of 4.8v, but if you don't know if that should be between 3 and 5, or 10 and 12 then it's rather useless information.
Just realised what a rant this has turned into, sorry.
I have been working in the trade for 16 years, 11 of them in dealers. One of the biggest problems you can have when talking to a customer is convincing them that what they read on a forum, is not necessarily what is wrong with their car.
Yes an engine still needs fuel, compression, spark. But once you found you have compression, it can be very difficult to find out why you don't have either spark or fuel or both. The most important thing to know is the facts about the particular car you are working on. Someone earlier said crank sensor is often the fault. This is true. But for instance a new Mercedes will still start and run using a reading from the camshaft sensor. But would run flat with the EML on.
What you really shouldn't do as instructed above is start throwing money at it, by replacing the cheapest parts first. A set of plugs will never be the reason a new car does not start. The chance of 4, 6, 8 or however many plugs your engine has failing all at once is almost impossible. The same can be said for individual coil packs. Yes they often go wrong, but that would just create a misfire.
Something like a misfire can still be diagnosed easily. Disconnect the coil packs one by one. When you unplug one and idle doesn't get even more lumpy, that's the cylinder at fault. But remember you still don't know if it's the plug, coil, injector, wiring loom or the control unit. Swap the coil with another. Try again.
Using basic unplugging and swapping technics lots can be diagnosed. But I would always recommend the fault codes are read. Then take those with a pinch of salt to.
Fault code says the upstream O2 sensor is faulty, so we replace it right? But what if it the air mass meter that has gone out of calibration. It is still working so the control unit doesn't see a fault. But it's richening up the mixture slightly which causes the O2 sensor to appear faulty. Or it could be a MAP sensor, or a knock sensor, leaking injectors, poor quality fuel, incorrect fuel, chafed or chewed through wiring, incorrect coding, inlet port shut off flaps stuck, or a seized EGR valve. The list goes on and on and is different for different brands and models.
Basically good modern diagnosis is still done using old fashioned techniques but using a computer to assist you. Most of the time a display of "actual values" is much more use than just a fault code. But most cheapo scanners won't do them or if they do, they don't give you the tolerances. It's fine to know a sensor is giving a signal of 4.8v, but if you don't know if that should be between 3 and 5, or 10 and 12 then it's rather useless information.
Just realised what a rant this has turned into, sorry.
I have been working in the trade for 16 years, 11 of them in dealers. One of the biggest problems you can have when talking to a customer is convincing them that what they read on a forum, is not necessarily what is wrong with their car.
It was me that mentioned coil pack. And the reason I said coil pack, not just coil, is because I was thinking of a car with and engine such as a zetec witha coil pack and HT leads, therefore a coil pack failure could result in a non starting car.
With Individual coils that won't happen, unless all of them fail together, which is highly unlikely.
With Individual coils that won't happen, unless all of them fail together, which is highly unlikely.
In the case of the vehicle the OP mentions you can do a pedal test, gas and throttle down, switch ignition to pos 1 and it will flash the engine management light at you in a certain sequence, this is the OBD2 code for an issue the car either has or is experiencing. Video here: https://youtu.be/zyCanc7BheU
Newer Vauxhalls just display the fault code in the odometer.
Many modern cars have a similar way of accessing fault codes.
Note that a stored code may not be active - all we know at this point is the car has experienced a fault at some point. While the car is running well its a good practice to reset the stored codes (there is usually a procedure) so when a problem is experienced you know it is current. If you buy a better code reader it will tell you if the fault code is active or not.
Another tool to use is a cheap OBD2 data reader. This will stream live data from the ECU and display it. This can be invaluable at times - I can give an example. Vauxhall 2 litre XE engine in a caterham. Engine has been rebuilt but refuses to fire, fuel present but no spark. Timing is correct and ignition system components are known to be good but we have no spark. By use of a data reader (actually a tech2 machine in this case) it was determined that the crank sensor, whilst not throwing a fault had poor/inconsistent signal. Further testing with an oscilloscope determined the trigger point in the crank disc (60-2 tooth wheel) was not being detected. Engine came back out and the trigger disc was found to be slightly bent, probably dropped at the machine shop/assembly stage and overlooked.
If the ECU gets a poor or non existent signal from a sensor, especially a critical one its just not going to behave as expected. Expected output/ranges can be found in autodata books.
You will need some knowledge of how the management system works, but the same can be said of a carb & points engine - float levels, jet sizes, ignition advance springs etc is all witchcraft to me!
Whilst engine stuff is mostly standardised via OBD2 spec the problem with modern cars is its only one of a whole array of ECUs - there is one controlling power management, another one (at least) for media capability, another to control lights/wipers/windows etc, another one for stability, another for braking, another for air con and so on. There seems to be little standardisation in these systems so you end up needing a manufacturer specific tool (like VAGCOM for example) to obtain information from these control units.
Not used it myself but VAGCOM appears to be a worthwhile, inexpensive tool and well worth investment if you end up owning a VAG car for any period of time. There is a system called VAUXCOM for vauxhalls, its more expensive than VAGCOM but there are versions called OPCOM (I think its a knock off) thats very cheap and will do basic stuff. Even a tech2 isn't very expensive any more.
ETA: Just noticed some of this reflects what hamster69 says. Good to know I'm not too far wide of the mark
Newer Vauxhalls just display the fault code in the odometer.
Many modern cars have a similar way of accessing fault codes.
Note that a stored code may not be active - all we know at this point is the car has experienced a fault at some point. While the car is running well its a good practice to reset the stored codes (there is usually a procedure) so when a problem is experienced you know it is current. If you buy a better code reader it will tell you if the fault code is active or not.
Another tool to use is a cheap OBD2 data reader. This will stream live data from the ECU and display it. This can be invaluable at times - I can give an example. Vauxhall 2 litre XE engine in a caterham. Engine has been rebuilt but refuses to fire, fuel present but no spark. Timing is correct and ignition system components are known to be good but we have no spark. By use of a data reader (actually a tech2 machine in this case) it was determined that the crank sensor, whilst not throwing a fault had poor/inconsistent signal. Further testing with an oscilloscope determined the trigger point in the crank disc (60-2 tooth wheel) was not being detected. Engine came back out and the trigger disc was found to be slightly bent, probably dropped at the machine shop/assembly stage and overlooked.
If the ECU gets a poor or non existent signal from a sensor, especially a critical one its just not going to behave as expected. Expected output/ranges can be found in autodata books.
You will need some knowledge of how the management system works, but the same can be said of a carb & points engine - float levels, jet sizes, ignition advance springs etc is all witchcraft to me!
Whilst engine stuff is mostly standardised via OBD2 spec the problem with modern cars is its only one of a whole array of ECUs - there is one controlling power management, another one (at least) for media capability, another to control lights/wipers/windows etc, another one for stability, another for braking, another for air con and so on. There seems to be little standardisation in these systems so you end up needing a manufacturer specific tool (like VAGCOM for example) to obtain information from these control units.
Not used it myself but VAGCOM appears to be a worthwhile, inexpensive tool and well worth investment if you end up owning a VAG car for any period of time. There is a system called VAUXCOM for vauxhalls, its more expensive than VAGCOM but there are versions called OPCOM (I think its a knock off) thats very cheap and will do basic stuff. Even a tech2 isn't very expensive any more.
ETA: Just noticed some of this reflects what hamster69 says. Good to know I'm not too far wide of the mark
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