BMW Questions? Ask a BMW Repair Expert for Answers.
Hello and welcome,
Do you have any fault codes in the system?
What other monitors have run and passed?
Are you trying to get the monitor to pass for a emissions test?
ok what type of scan tool are you using?
Are you pulling codes from the 20 pin connector under the hood?
Most generic scan tools will not pull all the codes from the DME engine control module
How many miles have you drove it to try to pass the catalyst monitor?
First drive consistently between 20 and 30mph for approximately 4 minutes.
Then drive consistently between 40-60mph for approximately 15 minutes, some vehicle coasting time should be included.
This process with reset if engine speed goes over 3000rpm, or
if driving speed is over 60mph, or large fluctuations in acceleration.
If this occurs, stop the vehicle. Start and stop the engine and start the drive cycle procedure over again.
This is the drive cycle procedure to pass the catalyst monitor.
What is the LTFT at?
Has the maf been cleaned?
Why did you replace the downstream H02S?
Either the engine computer is picking up a partially failing catalyst or there is a fault with the DME
Does the rear o2 sensor readings look normal. What were the codes that the vehicle came in with?
It sounds like a catalyst is failing.
Ensure there is no intake or exhaust leaks
The catalyst outlet temp should be about 110 degrees higher then the inlet.
Do the tap test on the catalyst, should not have any rattling noises.
Post o2 sensors readings should hold steady and not fluctuate.
Also aftermarket cats do not work well on these engines and will fail the emissions test. ensure oem catalyst are used
Ok this is what i was thinking what was going on, it takes a lot of drive cycles before a cat code will set. The DME will go through a series of tests for the O2 sensors before it will set a p0420, or p0430.
so the rear bank is at .15?? this is a indication of a bad cat.