Having an issue with my 5.9 that started a couple days ago. Threw CEL while idling in the loading zone at Ikea. Pulled the codes when I got home, P0132(current) and P0138(pending). High voltage for the upstream o2 sensor (rich condition). Also noticed that intermittently when the truck is idling while at full temp, the RPM's will drop to ~300 and it will try to stall (this is what I think is causing the P0138 code to enter pending status).

First things I checked were relays and fuses. Fuses tested fine. My truck doesn't have (and has never had) relays in the O2 sensor heater sockets in the power distribution box. I think I read in another thread that the o2 sensors use the ASD relay, so I swapped it with the wiper motor relay that I knew was good, no change.

I replaced both sensors a few years ago with NTKs, so I was a little hesitant to suspect the sensor itself, but I ordered a new one and put it in today just in case. Didn't solve the problem...guess I've got a spare on the shelf now haha.

Pulled the #1 plug and it looks fine to me, no indication of a chronic rich condition. Truck runs perfectly fine in normal driving, no sputtering or power loss.

It's not the plenum, I fixed it right a couple years ago with a thick aluminum plate, shorter bolts, etc.

Next I made a homemade smoke machine(works great) to test for vacuum leaks. I had been experiencing the "wild vents" so I knew I had a leak somewhere, and figured that could be the root cause. Found a leak at my oil catch can, no other leaks. Bypassed the can, reset the CEL, and went for a drive. The "wild vents" issue appears to be solved, and I didn't get a light on the test drive, so I thought I was in the clear, but when I pulled in the driveway and left the truck idling, a few minutes later it started sputtering the threw the light again.

Watched some live data while idling and driving around. Upstream O2 sensor voltage seems to hover between 1v-1.2v while idling. Bounces around inside the normal range (0.1v - 0.9v) while driving around, so it's an issue only at idle.


So at this point, I'm thinking that some other engine system is causing a rich idle condition, and the O2 sensor/circuit itself isn't actually the issue. Tomorrow I'm planning on verifying that my exhaust manifold bolts are still tight (they like to work loose sometimes), then taking off the throttle body to clean the MAP, IAT, TPS sensors. Any other ideas?

 

Does your truck have bank 2 O2 sensors (depends on year, CA emissions, HD) ? If only bank 1 is going wonky at idle I'd think leaky injector or something. AFAIK only CA trucks have the additional heater relay.

 

Just a single upstream and single downstream.

Ok thanks, that makes sense. I was looking at the sockets and thinking "why would they put heater relay sockets in here and no relays?"

 

Ok, I've done a bunch of checking, still not solved yet.

I watched the live voltage data for the oxygen sensors(through ODB port, so this is what the PCM is seeing), and here's what I saw.

Cold start and cold idle (open loop) both sensors output 1v steady. Sit and rev, and nothing changes.
Driving around while still in open loop, the sensors continue to output a steady 1v.
Engine runs and sounds great.
Eventually it enters closed loop and the sensors begin functioning in a way that appears normal, bouncing between 0.1-1.0v while you're driving.
If you then stop and let it idle, it eventually will start losing idle speed, chugging, then a loud hissing begins to sound (IAC opening fully I think) and it stalls.

Codes I have seen today are still the P0132 and P0138(O2 high voltage), but also the P0135 and P0141 (O2 heater codes).

Pulled the plugs on both O2 sensor harnesses and tested them. With the engine running in open loop, both are getting voltage. I suck pretty royally with electrical, but from what I can tell, on the upstream sensor, the solid black is clearly ground, green/white wire and the black/white wires show 12v, and the orange/white is showing between 1-2 volts. At some point, as the engine continued to idle, it appears to enter closed loop, and both the green/white and the black/white wires lost their 12v power. I am not sure what to make of this.

 

Ok, so I'm fairly confident that for whatever reason, the O2 sensors aren't reaching temperature while idling. I think the extra heat from driving around warms them enough to get them into operating range, but just sitting and idling doesn't, so that is why they just read 1v all the time.

I don't get it though, the front sensor is brand new, and I resistance tested the one that came out and the heater circuit is intact, still need to resistance test the one that's now in the truck. Rear is only a couple years old, also an NTK, and it's also very unlikely I would think that they would both fail simultaneously. There's something else going on, I just can't seem to figure out what.

 

If things are working properly, you should see 12 volts on one wire, 5 volts on another, third wire is ground, fourth wire is signal return to the PCM. If you are seeing 12 volts on two wires, that is a problem. What year is your truck?

 

2001, 50 state emission accord to build sheet.


Ok, I re-checked, and with the engine running, black/blue being ground. On the upstream, I have 12v on green/white, which is correct. I have about 2v on the tan/white (service manual says this is the "oxygen sensor heater", and I have nothing on the remaining wire (service manual says it's brown and violent but mine is black and white. Manual says this is "Oxygen sensor heater control".

Downstream I also have black/blue ground and 12v on green/white, which are correct. I then again have 2v on the orange/black, and nothing on black/white. So again, no voltage to the "oxygen sensor heater control"

Wiring diagram is 8w-30-17 in the service manual, page 854 of the PDF



Also, turns out the drop of all voltage I talked about earlier was just me blowing the fuse with clumsy hands. Hard dumped the PCM just to check if that was the only problem, but got the P0132 code again almost immediately.

 

Have you replaced the sensor? (NTK or Denso brand please.)

According to theory, the code is for bank 1 sensor 1, but, by the wiring, you are testing bank 2 sensor 1..... I think only the HD 360 had two front O2 sensor, aside from the california models..... What's the eighth digit of your VIN?

 

I replaced both sensors a couple years ago (NTK), and I replaced the upstream a couple days ago when the issue first started (also NTK).

P0132 is the first code that shows up, but the P0138 for the rear, and the P0135/P0141 for the heater circuits to both also usually show up eventually.

My truck only has 2 sensors, an upstream and a downstream. They're listed as Bank 1 Sensor 1 and Bank 2 Sensor 1 in the fault codes. The harness connectors are different, and their locations are very distinct, no way to mix them up.

Z is the 8th digit(light duty)

 

Agree with your reasoning that the 02 heaters could be the problem. The heaters get power via the ASD on the dark green/white wire and the PCM activates them by grounding the brown/white or brown/violet wire (color depends on sensor location). You have 12 V on dg/wt, and when the PCM activates the heater there should be no voltage differential between sensor control and ground. So not sure what to think of the 2V you measured. Could be a PCM grounding issue or wiring.

The PCM doesn't really monitor the heater circuit, it just sees that the sensor signal isn't working some time after the heaters are turned on and concludes there's a problem with the heater. I'd disconnect the sensors and see if the heater circuits correctly switch a load like a light bulb.