After installing MAC headers, I started getting the infamous SES light randomly. The car was scanned and it was the EGR, but the problem is that the EGR valve is working properly, actually everything is working properly and is functional. My mechanic said that the reason why I'm getting an EGR fault code is because of the "reduced backpressure in the exhaust" and this can make the car fail emissions. Does anyone have a similar problem? And if so, what should I do? By the way this is a 1995 OBDII Z28, I also have a flowmaster exhaust installed...any help would be appreciated...

 

If you have an OBD-II 1995, you may have a rare car. Never been one documented yet. All 95's have the OBD-II 16-pin ALDL connector, but the PCM is OBD-I. What specific code did the mechanic get? There is one code for EGR flow, and another for the EGR solenoid.

Low back pressure will cause the PCM not to see the required change in MAP pressure when it commands the EGR valve to open. This does seem to happen much more frequently with OBD-II diagnostic routines than with OBD-I, but it does happen with both. I think there might even have been a recall for overly sensitive EGR valves on some of the 96/97 models. I've seen some posts from people who claim they have manged to make the MAP signal appear to respond when the valve is commanded to open, but isn't there. The last alternative would be to have the EGR operation "programmed out".