Lambda sensors or cat convertors
Discussion
I need some advice please. My car failed the MOT on emissions. What would be the best part to check first to see if it needs replacing, the Lambda sensors or the cat convertors. What's the easiest to check to see if it is duff and do the parts need to be removed for this to be done. thanks in advance.
Could be a multitude of things but knowing the S6 your probably in the right ball park with Lambda sensors and/or Cat/s.
If you have an analogue Volt meter you can test each lambda sensor. The volt range to select is ideally 0 to 1V DC altho 0-5V is adequate as all you are looking for is a continuous deflection of the pointer between 0 and 1 V.
Run the car until it is warmed up and then stop it. First determine which of the 3 wires out of the lamba sensors are 12V DC and ground (you will need the ignition on). You then want to connect between the other wire (which is the signal wire) and ground. Start the car up and observe the meter for the pointer fluctuating between 0 and 1 v. Both Lambda's should be performing very similarly, if they are this rules out the sensor/s.
The cats are notorious for collapsing internally. To check you do need to remove them. a collapsed cat is obvious.
I have read on here about folk de catting and the car still being able to pass the MOT test. My immediate opinion is that they have been very lucky, but I do belive that it may be possible to set up the ECU fueling (with the lambda probes disconnected) as near as damn it stochiometric. Then reconnecting the lambdas the ECU should in theory provide more accurate closed loop control which should allow the car to pass the MOT test.
Good luck
G
If you have an analogue Volt meter you can test each lambda sensor. The volt range to select is ideally 0 to 1V DC altho 0-5V is adequate as all you are looking for is a continuous deflection of the pointer between 0 and 1 V.
Run the car until it is warmed up and then stop it. First determine which of the 3 wires out of the lamba sensors are 12V DC and ground (you will need the ignition on). You then want to connect between the other wire (which is the signal wire) and ground. Start the car up and observe the meter for the pointer fluctuating between 0 and 1 v. Both Lambda's should be performing very similarly, if they are this rules out the sensor/s.
The cats are notorious for collapsing internally. To check you do need to remove them. a collapsed cat is obvious.
I have read on here about folk de catting and the car still being able to pass the MOT test. My immediate opinion is that they have been very lucky, but I do belive that it may be possible to set up the ECU fueling (with the lambda probes disconnected) as near as damn it stochiometric. Then reconnecting the lambdas the ECU should in theory provide more accurate closed loop control which should allow the car to pass the MOT test.
Good luck
G
If you know how the engine management system works and have the appropriate diagnostic tools then it is possible to diagnose problems like this yourself, but I don't get the impression from your post that you do. To be on the safe side I suggest you get an expert to fix it. The engine management system is moderately complex and not easy to diagnose by trial and error, and there are plenty of ways to damage it while you're trying to find out what's wrong. Getting it fixed by an expert needn't be expensive, in fact it may turn out cheaper than doing it yourself by trial and error.
Thanks for the replies guys. I wouldn't dream of trying to fix the problems myself, i'm just interested in the how/what the solutions would be. I have a friend who is a mechanic who i trust implicitly and he will do the work for me. It's always good to know that people will take the time to offer help and advice. Thanks again.
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