Cel P0402/p0171/p0174

[nola mike]

Have had intermittent issues with the last 2 codes (banks 1&2 too lean) triggering the CEL. Got a fancier scanner to do some more diagnostics, and noticed the first code now also showing (EGR flow excessive). All of my fuel trim codes (SHRTFT/LONGFT) are at -100. All of the O2 sensors are showing 0v (from the scan tool, not directly measured). Looking around, it seems that a bad DPFE will throw these codes, although it looks like more often it's too little EGR flow. So, here are the questions:
1. Could a bad DPFE (or stuck open EGR valve) be the culprit here? would too much EGR flow result in lean conditions?
2. Are my FT and O2 sensor readings just indicative of the engine attempting to maximally enrich the mixture, or is there a problem with the O2 sensor signal to the computer? Of note, when watching the live data, I get no voltage fluctuation at all, even when engine is cold (it should be in open loop, right? not at 0v yet...) or with changes in rpm.

any other thoughts?

 

[Earl43P]

See how it acts with the EGR valve's vaccum tube disconnected. Clear the codes and drive it a day like that. If it still indicates excessive flow (with no flow possible), expect a new DPFE to fix that code.

STF and LTF don't change?
O2 shows no switching / values are always 0?
Check their fuses (labelled HEGO) and replace the O2's (upstream only) if that is the case. O2's values "drive" the SFT and LFT, so if the O2s are bad, the computer is simply using default values. Must run pretty crappy / with bad mpg.

At the very least, disconnect the O2's and examine their connector contacts for corrosion. It appears that both are bad.

 

[nola mike]

See how it acts with the EGR valve's vaccum tube disconnected. Clear the codes and drive it a day like that. If it still indicates excessive flow (with no flow possible), expect a new DPFE to fix that code.

well, after clearing the codes yesterday (prior to this advice), nothing is showing back up, pending or otherwise. when i've cleared them in the past, it's taken hundreds of miles to show back up. still have the same o2/SFT/LFT values though. i don't expect to be able to tell much from disconnecting the EGR valve.

STF and LTF don't change?
O2 shows no switching / values are always 0?
Check their fuses (labelled HEGO) and replace the O2's (upstream only) if that is the case. O2's values "drive" the SFT and LFT, so if the O2s are bad, the computer is simply using default values. Must run pretty crappy / with bad mpg.

fuse looked ok. actually runs fine, completed 9200 mile road trip with a 1200# slide in camper getting 18-19mpg. looks like i'm getting about 22-24 without it. doesn't seem too bad.

At the very least, disconnect the O2's and examine their connector contacts for corrosion. It appears that both are bad.

contacts looked ok on one at least. it was getting dark...
so you're saying that i have 2 bad o2 sensors? seems unlikely that both (all 3?) would fail at once. shouldn't at least one be registering some voltage running in open loop? i was trying to measure voltage directly at the sensor, but i'm not sure which wire is the sensor wire. i got 12v off the harness going to the connector, but couldn't get voltage from the other wires--i was only messing with 1 sensor today. why wouldn't i get a failed o2 sensor code? how would that lead to the EGR code?

 

[nola mike]

so i removed an o2 sensor today and bench tested it; was able to get .45v with a propane torch. so maybe i really am running a super lean condition? dunno, still seems like i should get SOME voltage there, at least at startup. also checked the dpfe; KOEO i was getting 2.5v (should be .55 or 1v). would an a/f meter help me here? if i have a problem with o2 sensor/harness/whatever such that it's telling the PCM that i'm running lean, then the engine should be trying to enrich--and my actual mixture should be rich. if the sensors are actually doing their job, and the mixture is really lean, then i should be able to pick up on that with the meter as well...