PO155 2002 Chevy S10 4x4 4.3L 176,000 miles

Boomer

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Make
Chevrolet
Model
S10
Year
2002
Miles
176,000
Engine
4.3
The SES light came on. I checked it. It was PO155. Bank 2 Sensor 1 heater circuit malfunction. The heater wires on the sensor showed no continuity. I replaced it. Next up came PO138. Vehicle ran fine. I thought great, another sensor is bad. I cleared the code. It has not come back however, the PO155 comes back all the time now. I keep clearing it and it comes right back. I checked the new sensor and the heater circuit is ok. I checked the other upstream sensor. Heater wires have continuity. Ok, maybe it's the vehicle wires. I put my meter on the vehicle side of the harness on the terminals corresponding to the heater circuit. When I turn the key to the run position. I get system voltage. This happens on both upstream sensors. I could just replace the one I haven't replaced since I have a brand new Bosch for it on hand. I really hate being a parts changer and the old sensor has continuity just like a new one. Should I just replace it and see what happens?
 

billr

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With those two codes, it seems likely there is a short in the harness that goes to those two sensors. Do lots of visual inspection along the whole length of the harness. You may even have to open the harness up to expose the actual wires.
 

Mobile Dan

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Use your meter to compare RESISTANCE of the heater circuit of both upstream sensors. Maybe the PCM (sometimes) thinks the resistance of the heater circuit of the new sensor is too high, and codes it as "open circuit".
 

Boomer

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With those two codes, it seems likely there is a short in the harness that goes to those two sensors. Do lots of visual inspection along the whole length of the harness. You may even have to open the harness up to expose the actual wires.
Thanks Bill. Only one code now. PO155
 

Boomer

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Use your meter to compare RESISTANCE of the heater circuit of both upstream sensors. Maybe the PCM (sometimes) thinks the resistance of the heater circuit of the new sensor is too high, and codes it as "open circuit".
Thank you for the reply. I will try that. That's interesting. It must think that a lot because the light comes on pretty quickly
 

billr

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Sure, you have no P0138 now, but it went away with no apparent fix; correct? An intermittent like that, with a circuit that probably has wiring in the same bundle as the circuit giving the P0155, makes me more suspicious of the wiring than either of the two separate sensors. The harness is an obvious "common factor" for those two codes.
 

Boomer

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Sure, you have no P0138 now, but it went away with no apparent fix; correct? An intermittent like that, with a circuit that probably has wiring in the same bundle as the circuit giving the P0155, makes me more suspicious of the wiring than either of the two separate sensors. The harness is an obvious "common factor" for those two codes.
Yes, funny thing is. It didn't come up until I replaced the Bank 2 Sensor 1. Cleared it and hasn't returned.
 

Boomer

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Use your meter to compare RESISTANCE of the heater circuit of both upstream sensors. Maybe the PCM (sometimes) thinks the resistance of the heater circuit of the new sensor is too high, and codes it as "open circuit".
Thanks for the reply, Dan. I did this and had about 13.9 ohms. I'm not sure what the PCM expects to see but, the original AC Delco sensor had the same as the new Bosch so, I'm guessing that was in range?
 

billr

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Measuring current in the heater circuits may give some clues. Don't want to bother putting your ammeter in series? Clamp-on ammeters that read DC as well as AC are pretty reasonably priced these days.
 

Boomer

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Measuring current in the heater circuits may give some clues. Don't want to bother putting your ammeter in series? Clamp-on ammeters that read DC as well as AC are pretty reasonably priced these days.
I do have a clamp on that does DC. I can check it. I went ahead and installed the other new 02 sensor and now within two key cycles. I will get P0135 AND P0155. By two key cycles I mean. I can clear the codes. Drive to work. Leave work and in short order the light comes on. It always stores the code as pending first. Then a separate code for “confirmed” With no drive ability issues. Im wondering if I may need a PCM update? Obviously, I’ll check the other stuff first. Maybe try and look at some freeze data when it happens.
 

billr

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We need somebody to post an electrical schematic of these O2 sensor heater circuits. You have P0155, P0135, and P0138; all related to heater circuit "malfunction". I doubt this is a PCM issue, especially not just a program corruption that could be solved by reloading the program or updating it.
 

Boomer

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We need somebody to post an electrical schematic of these O2 sensor heater circuits. You have P0155, P0135, and P0138; all related to heater circuit "malfunction". I doubt this is a PCM issue, especially not just a program corruption that could be solved by reloading the program or updating it.
Bill, just to be clear. I do NOT have the P0138. I didn't get the P0135 until I changed Bank 1 Sensor 1
 

billr

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I understand that the P0138 has been gone for a while, but it did pop up during all this. My point is that all three of those codes have made an appearance at one time or another, and each the three indicate a problem with a different sensor circuit. The common factor is either the PCM, or any power feed/harness that goes to all three.

PS: every time you disconnect/reconnect a sensor you "wiggle" the harness a bit. Effects you see when changing sensors may have nothing to do with the sensor itself.
 

Boomer

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Ok thanks. Just wanted to make sure you weren’t under the impression that it was still there .
 
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