Evening all,

Once again many thanks for your responses. I appreciate the time and effort you have put in for me on what I feel is not a straightforward problem.

The customer doesn't really care about the EML being illuminated and will not spend a lot of money to fix this. His prime concern is the MOT Emission failure and this will be my priority. He and the garage assumed that the two items were related which is why I posted on both subjects. I would have assumed and please correct me if I am wrong, that the heater circuit would not create an MOT emission failure IF the HO2 sensor was in closed loop at the time of testing (assuming of course that the CAT was properly lit up and functioning correctly). I was with the vehicle for a long time time and I am assuming the HO2 sensor was heated naturally by the exhaust down-pipe. It certainly was in a closed loop situation which is why I got a max of 0.1% and 80ppm HC. The failure was down to a slightly high Lambda reading which I put down to a blowing exhaust. If I revved the vehicle at about 3500rpm (outside MOT testing specs) the Lambda reading would be within limits. So it might have failed again because the garage did not allow time for the HO2 sensor to get heated enough and was not in closed loop. I will see on my next visit. I know the customer will not pay for another sensor just to get his EML extinguished but I am interested enough to find out the cause of this problem.

Mike. Yes you are right. When I look at other peoples problems posted on here, then I do want to see what the emission figures are if applicable. I do not normally have trouble with emission problems and did not post the full details of them because I thought I had it sussed with the blowing exhaust which is why I only gave it the briefest of detail. As far as the PWM issue is concerned you are again right and it is a "black hole" that I have in my knowledge which I must try and remedy. Nice to get a chuckle from a M.O.M. though!


Regards

Pete M