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Question -
Ed,
Thanks for the reponse. I may have confused the issue with all the history, so let me focus on the current situation, and ask some specific questions:
1. I don't have a driveability problem -- that was solved by changing the fuel filter. My only symptoms right now are P0404 and P0405 codes. Also, I did drop the cats & check back pressure before I found the fuel filter, and things seem OK there.
2. How EXACTLY does a P0404 get set? Is it all from the EGR position sensor, or are the MAP & IAT sensors involved? I am getting the code as soon as the engine is warmed up & I accelerate.
3. A P0405 is "EGR sensor circuit A low", according to my book. Which sensor is sensor A? I have started getting this code shortly after I start the engine, before it even warms up.
4. I have seen some references to the PCM 'learning'/'relearning' the EGR valve position; can you give me any details on that?
5. In your experience, what are the odds that the EGR is bad, even though it tests basically OK? It's a pricey part to replace blindly.
Thanks,
Al
AnswerHi,Al
Got it,i forgot about your P0405,EGR position sensor circuit low voltage,i think we need to chase this code first,problem is is that that ckt is the 5 volt ref signal to the EGR MAP,and fuel tank pressure sensor from the VCM/PCM,take a look at your manual,and find the ckt 474 its a gray wire,its is located at all of those sensors,you need to use a DVOM and get a voltage reading from that gray wire ckt 474,it usually will be around 4.2 to 4.7 volts,if its under .14 volts we have a short in that ckt,and this will cause a position error for the EGR,the PCM supplies 5volts to that gray wire ckt 474,if it sees no feedback it will flag open,if it sees to low of a feedback it'll flag the P0405,now with DVOM,if voltage is low at .14 volts disconnect the EGR connector and see if voltage goes high to about 4.0 to 4.8,if it remains at .14 volts go to the MAP sensor and do the same,and finally to the fuel tank pressure sensor,what you are doing is cancelling out who is dropping or shorting the 5volt ref,or if in fact the wire itself is shorted to ground.
The p0404 is set by a difference between the actual EGR position and the desired EGR position is more than 10 percent for 10 seconds,this is how it is stated in GM's service information.again it the PCM sends ref voltage,the EGR position sensor according to were the pintle is,sends a return to the PCM,the PCM then calculates the position of the EGR pintle based on the voltage return,if we have a 5 volt ref ckt that is very low,and the EGR sends a signal that is very low,yet the PCM is expecting a higher return voltage,what do we get?we get a faulty return signal and the PCM flags a code,what do you think?worth looking into that gray 474 ckt and see if the voltage is were its suppose to be.
ED
