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

Boomer

Hero Member
Joined
Mar 14, 2007
Messages
324
Points
16
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

wrench
Staff member
Joined
Mar 12, 2007
Messages
7,172
Points
63
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

wrench
Joined
Mar 1, 2002
Messages
3,804
Points
48
Location
Kentucky
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

Hero Member
Joined
Mar 14, 2007
Messages
324
Points
16
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

Hero Member
Joined
Mar 14, 2007
Messages
324
Points
16
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

wrench
Staff member
Joined
Mar 12, 2007
Messages
7,172
Points
63
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

Hero Member
Joined
Mar 14, 2007
Messages
324
Points
16
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.
 
Top