Oxygen Sensor Heater Codes

[INW-Iron-Steel]

I changed the upstream O2 sensors on my 04 Sierra this last week and now I am getting P0135 and P0155 heater performance codes for the corresponding sensors. Two things I think are strange. 1- I didn't have either of these codes before starting. 2- It can take multiple days and many trips for the codes to trip. For example, after I reset the codes over the weekend, it took until I was driving home from work last night for the engine light to come back. Same codes. So 4 days for the PCM to recognize a deficiency, which seems a bit excessive to me. I am leaning towards bad (new) oxygen sensors right now, but I am interested to see what others think.



Here are the codes. I should have mentioned I had the battery disconnected when I replaced the sensors, but I will check the fuses today. I also replaced the sensors with Denso's in an attempt to get quality parts. The ones I pulled out were Bosch's, so the downstream sensors are still Bosch.

 

[stutaeng]

I've had good luck with Denso O2 sensors. Unplug the sensor and check the heating element with a DVOM for continuity (I believe it's the 2 black wires?). If they are okay, then probably not the sensors.

Since both banks are setting codes, I'd study a wiring diagram to see if they are on a shared circuit. Maybe a wiring issue like a ground intermittently failing. Also, check Charm.li for troubleshooting procedure for those codes.

Why did you initially replace the sensors?

 

[INW-Iron-Steel]

A little bit more backstory for context. I have been chasing some issues for about a month or so on the 04. My wife was driving it and told me it was slipping and not shifting well at slow speeds. It would not do it for me, but one day it was so bad she couldn't even get the truck to move and reported a loud bang from underneath. We've got about 30,000 miles on the rebuilt transmission, so I figured something was going bad just outside of the warranty. Looking at the build sheet I noticed the shop had not changed the shift solenoids. So, new fluid, filter, shift solenoids and EPC solenoid. I was in there, so I also did a Sonnax pinless 1-2 piston.

After putting it back together I took it for a drive and it finally did act up for me, and it was clearly a horrible misfire that was dropping engine RPM very low. I had my scanner in the truck but there was no engine light. No codes stored. I took a look in the GM enhanced portion of my scanner and found multiple codes.



P0154 also comes up as "O2 sensor no activity detected" when looking into these trouble codes. Then I got to thinking. The MAF on the truck was original with 270K miles, and the O2 sensors had at least 100K miles on them (I think my dad bought the truck with 155K and we did Headers/Y-pipe almost immediately). Looking at live data my fuel trims on bank 2 were also off. So, I replaced the MAF with a Delphi and the upstream O2s with Denso. The truck runs great, but now I am getting the heater codes for both upstream sensors that I replaced.

I forgot to mention that I also addressed most of the major grounds in the midst of this fiasco. New negative battery cable and terminal end for the coil ground on the front driver side of the block. Cleaned ground from battery to chassis near the bumper on driver side and replaced wire going to battery. Removed and cleaned grounds on driver frame rail under cab.

 

[INW-Iron-Steel]

I've had good luck with Denso O2 sensors. Unplug the sensor and check the heating element with a DVOM for continuity (I believe it's the 2 black wires?). If they are okay, then probably not the sensors.

Since both banks are setting codes, I'd study a wiring diagram to see if they are on a shared circuit. Maybe a wiring issue like a ground intermittently failing. Also, check Charm.li for troubleshooting procedure for those codes.

Why did you initially replace the sensors?

Thanks for the advise. I am going to check fuses first and then I will check for continuity on the sensors themselves. What I am slightly confused about is bank 1. I wasn't having any issues with bank 1 before. Fuel trims and voltage (on the scanner) looked good on bank 1. And no codes. I only replaced it because the bank 2 sensor was failing and I always replace O2 sensors in pairs.

 

[stutaeng]

Ah, ok that makes sense. Well the loud bang doesn't sound good though. So the MAF codes and the misfire codes didn't come back? That's odd that it got fixed with a new MAF + O2 sensors, but maybe they were bad.

I think the P0154 code of that circuit only runs the heater for a few seconds to heat the O2 sensor so engine can go into closed loop faster. I don't believe it affects any driveability. Probably only matters in the colder months. I had one show up on my 99, but my buddy suggested I just toone it out...SMH

Here's a generic 03+ wiring diagram for the O2 sensors:



I highlighted what seem like the heater circuits to me, and power from the fuseblock. Check the easy things first like the fuse.

 

[Tonimus]

Sorta related; bought my '06. Ran great, put 200 miles on it, no problem. Get a CEL around town for MAF sensor function. Hose out the sensor with MAF cleaner, clear the light, no more issues for another 200 miles. Going camping and halfway up the rim, I get a CEL. Too rich bank 1 and 2. Long term fuel trims are -18% and -19.5%. Short term are fine, so it's not CRAZY rich.

Lots of thinking about it. Went to a wrecker, got a Denso MAF, cleaned it and installed it. Threw a 20oz can of SeaFoam injector cleaner in half a tank. Ran that tank almost dry. Filled it back up. 25 miles into the new tank, light goes out. Long term trims are now -4% and -4.5%. $20 for junkyard MAF, $17 for a big can of SeaFoam.

As far as the heater performance code, I suspect the computer is looking at ambient air temp when factoring how long the O2 sensor should take to heat up. Probably a lookup table for that. It's entirely possible it's marginal and takes several cycles to detect. You could also disable that DTC pretty easily for around the same price as two new sensors, then you have the bonus of an extra tool.

 

[INW-Iron-Steel]

Ah, ok that makes sense. Well the loud bang doesn't sound good though.

I attribute the "bang" she heard to an exhaust pipe smacking the frame as the engine was trying to idle at like 200-300RPM while misfiring like crazy. I also think the low RPM was causing the not moving forward issue from probable low line pressure in the transmission. Either way, transmission is fine which is a good thing!

So the MAF codes and the misfire codes didn't come back? That's odd that it got fixed with a new MAF + O2 sensors, but maybe they were bad.

MAF and misfire codes are gone and haven't come back.

I think the P0154 code of that circuit only runs the heater for a few seconds to heat the O2 sensor so engine can go into closed loop faster. I don't believe it affects any driveability. Probably only matters in the colder months. I had one show up on my 99, but my buddy suggested I just toone it out...SMH

I think you may have meant P0155 and not P0154? P0154 is "Heated O2 sensor (HO2S) insufficiency" where the P0135 and P0155 are "HO2S heater performance" codes.

Here's a generic 03+ wiring diagram for the O2 sensors:
View attachment 3586


I highlighted what seem like the heater circuits to me, and power from the fuseblock. Check the easy things first like the fuse.

Thanks for the diagram!

 

[INW-Iron-Steel]

O2-A and O2-B 15amp fuses are good. Now, I cleared the codes last night when I got home. After checking the fuses I plugged the scanner back in and fired it up. The heater codes are back pending after the first cold startup. I cleared them again, shut the truck off and then started it back up. No code. Drove to the gas station, shut it down and restarted, nothing pending. I think I cycled the key another two times on this test drive, and then hopped on the freeway. I was watching short term fuel trim and O2 voltage. Anyway, no stored codes after a 20 minute or so drive and the 'readiness monitors' are nearly all green.



I am assuming the O2 heater function is only triggered on cold start. I'll let it sit for a few hours and try starting it again to see if the codes come back. I am starting to lean towards these O2 sensors being faulty. Fuses are good and the only change I made was the sensors themselves. Prior to that the heater functionality was fine. I ordered some Delphi sensors from Amazon which should be here Sunday. After I see the code get set again, I will pull these, check continuity, and take them back to Autozone. I essentially got these for free with a giftcard someone had given me, so I'm not too broke up about it.

 

[Tonimus]

After I see the code get set again, I will pull these, check continuity, and take them back to Autozone. I essentially got these for free with a giftcard someone had given me, so I'm not too broke up about it.

Continuity probably won't show anything wrong, if you're only getting a performance code. I'd suggest a test light to verify the heater can carry current.

 

[INW-Iron-Steel]

You could also disable that DTC pretty easily for around the same price as two new sensors, then you have the bonus of an extra tool.

Just curious, what tool would that be?

Continuity probably won't show anything wrong, if you're only getting a performance code. I'd suggest a test light to verify the heater can carry current.

That is an even better idea, thank you!

 

[Tonimus]

Just curious, what tool would that be?

That is an even better idea, thank you!

OBDX Pro VX - OBD2 Diagnostics and Tuning - OBDX Pro

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Combined with PCM Hammer and Universal Patcher, you can disable those codes. You can either uncommand the CEL, or disable the code altogether. That's what I used to disable VATS.

 

[INW-Iron-Steel]

Delphi ES20094 installed as upstream sensors on the 04 this afternoon. No pending codes after initial cold startup, I guess we'll see if that lasts. Live data on the scanner looked good also. Not sure if this is related, but the resistance on the heater circuit between all of the brands was different. The Bosch sensors I had removed measured 12 ohms, the Delphi measured 10 ohms, and the two Densos measured 6 ohms.

Now to see if I can get Autozone to take the Densos back. The initial attempt resulted with a manager telling me "Well these are used, you can't return these." How else would I be able to tell you they are faulty?

 

[ORVietVet]

AZ was selling used oxygen sensors?

 

[stutaeng]

I would just try to get Autozone to warranty them. But now that I think about it, I've never actually have warrantied anything from the local parts stores?

 

[INW-Iron-Steel]

AZ was selling used oxygen sensors?

Haha! No, they were new. After I installed and ran them for about 5 days I took them back and told them they didn't work. I tried to explain the heater circuit issue but the manager was just looking at me with a confused blank stare. All he seemed to be able to say is I couldn't return them because they were used. But then I was confused. What is the point of a warranty if I cannot return a faulty part?

 

[INW-Iron-Steel]

I would just try to get Autozone to warranty them. But now that I think about it, I've never actually have warrantied anything from the local parts stores?

Not a bad idea, but I'd have no use for them. I wouldn't risk having the same issue again. If I need downstreams I'd get Bosch or Delphi from Amazon, they're cheaper anyway.

I haven't had good luck getting parts warrantied at local chains. I don't buy much local for many reasons including that. I buy from Summit whenever I can, even for the OE stuff. Easy to get free shipping, top notch customer service, and they usually have the package at my door within 2 days.

 

[ORVietVet]

Haha! No, they were new. After I installed and ran them for about 5 days I took them back and told them they didn't work. I tried to explain the heater circuit issue but the manager was just looking at me with a confused blank stare. All he seemed to be able to say is I couldn't return them because they were used. But then I was confused. What is the point of a warranty if I cannot return a faulty part?

Ok, I misunderstood the context. I would tell the AZ employee, "Of course they are used, you freakin' idiot, that is how I found out they are faulty".

 

[ORVietVet]

Not a bad idea, but I'd have no use for them. I wouldn't risk having the same issue again. If I need downstreams I'd get Bosch or Delphi from Amazon, they're cheaper anyway.

I haven't had good luck getting parts warrantied at local chains. I don't buy much local for many reasons including that. I buy from Summit whenever I can, even for the OE stuff. Easy to get free shipping, top notch customer service, and they usually have the package at my door within 2 days.

I have had the opposite experience. At my local AZ, I have had to warranty I part. Took it back, no questions asked, except, what was my concern with the part?