My son's 94 trans-am started throwing the SES light awhile ago. I am reading DTC 27 & 32, EGR electical fault and EGR system fault. I think 27 is a solinoid problem. Can this also cause the DTC 32?

Also, the car failed test only smog in the people's republic of california, the NO limit is about 689 ppm, and 794 was measured @15 MPH, at 25 MPH, limit = 706, measured 478. So it failed at 15 MPH, but passed at 25 MPH. Could the EGR and/or the EGR solinoid cause this behavior? Any tips on how to get the NO @ 15 MPH below 689?

Thanks.

 

The specific puprose of the EGR system is to reduce NOx emissions. You are correct..... DTC 27 tells you there is an electrical fault in the EGR vacuum solenoid circuit. Could be wiring fault, a fuse (although not likely, since it shares the fuse with a couple other things that would also set codes for a blown fuse), or a faulty solenoid. If the solenoid is not opening when commanded, the EGR valve won't work. DTC 32 detects low/no flow through the EGR system when it is supposed to be operating. All things point to the EGR system as being related to the NOx failure.

But.... what did the CO and HC levels look like? Were they generally a lot lower than the failure limit? If so, it may indicate the engine is running lean, which reduces CO and HC, but elevates NOx. Or were CO, HC and NOx all relatively high, indicating the possibility of a deceased cat?

 

____________MAX Measured
HC@15MPH___83___68
HC@25MPH___48___42

CO@15MPH__.48% .24%
CO@25MPH__.46% .35%

 

OK, 15 MPH is the problem. Based on your thoughts above, I believe the engine is running lean. So, do I just swap the solinoid? Is there a way to use data master to see if I have improved before I go back for another test?

 

I am looking at the shop manual for the EGR. The PCM outputs a discrete that controls the solenoid. How would the PCM throw a DTC 27? I don't see any detection capability for the solenoid electronics. How would it know that the wire or solenoid is not working? I can send any interested party a copy of the pages from the shop manual via email.

 

On most of the solenoid checks, the PCM looks at the voltage with the switch in open and closed positions. The voltage should be low when the circuit is "on", and near +12V when the ciruit is "off". The code sets when the PCM sees a voltage near +12V when the circuit is commanded "on", or the PCM sees a voltage near "0" when the circuit is commanded "off".

I think looking for the problem would make more sense than questioning the design capabilites of the GM engineers