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Dan, Technician
Category: Cadillac
Satisfied Customers: 24443
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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2003 Cadillac: I replace the O2 sensor..CTS...error codes

Resolved Question:

I replace the O2 sensor in my 2003 Cadillac CTS. I am still getting 2 error codes, P0161 and P0160. Why will these not go away?
Submitted: 8 years ago.
Category: Cadillac
Expert:  Dan replied 8 years ago.

Check the PRE HO2S and POST HO2S fuses located in the under hood fuse block with the key on to verify they have power and fuses are in good. If they are good at this point you need to do a resistance test between the sensor and pcm on each of the wires. It could be a bad connector, if wires test out ok replace pcm. Let me know if you have questions. Thanks



P0161 Heated Oxygen Sensor (Bank 2 Sensor 2) Heater Circuit Malfunction

Possible CausesSetting Conditions
  • HO2S heater high side driver circuit has high resistance (open)
  • HO2S heater low side driver circuit has high resistance (open)
  • HO2S heater Ignition circuit is open (check the POST O2 fuse in fuse block)
  • HO2S heater element has failed
  • ECM has failed

P0160 Heated Oxygen Sensor (Bank 2 Sensor 2) Insufficient Activity

Possible CausesSetting Conditions
  • Check for air leaks in the exhaust manifold and in the exhaust pipes
  • Check for a restriction somewhere in the Exhaust system
  • HO2S air reference hole plugged (check for dirt on the outside)
  • HO2S signal circuit is open, or the low reference circuit is open
  • HO2S has failed (it may be contaminated with fuel, silicone or water)
  • ECM has failed



Customer: replied 8 years ago.
I checked the fuses and they are fine. I will have somebody who knows how to run the restiance test on the pcm do that.
Expert:  Dan replied 8 years ago.
Alright and when you do the resistance test between the sensor and pcm this will verify what the problem is. Let me know if you have questions you can respond to this answer at anytime even after you accept. Thanks
Dan and 2 other Cadillac Specialists are ready to help you
Customer: replied 8 years ago.
OK We took the sensor from the drivers side and put it in the passenger side and the P0161, and P0160 codes went away so it isnt in the wiring or communication. Then we put the new sensor in the driver side and got the same codes for that side, P0141, P0140. We assumed that this meant that the sensor was bad so we exchanged it for another new one, same codes. Is there something special that a GM technician has to do to reset this code or what? Why won't they go away!
Expert:  Dan replied 8 years ago.
At this point you need to do a resistance test between the oxygen sensor and the pcm to verify the cirucit is good if so replace pcm. Let me know if you have questions, thanks.
Customer: replied 8 years ago.
How could it be the PCM if the other codes went away when we hooked up the old sensor to the passenger side? The codes switch according to where we put the new sensor... Is it possible that the sensor has to be programed or something before it is installed? How expensive is a new PCM and wouldn't there be more problems if it was the PCM not just the O2 codes?
Expert:  Dan replied 8 years ago.
It is possible the pcm could be the problem and only be throwing those two codes. It does not have to be programmed. You can get a used pcm from to save money. If the new sensor sets a code for whatever side you put it in this makes me think it is a sensor problem. Do a resistance test on both new and old sensor to see if resistances are the same. If so you will need to do a resistance test on the oxygen sensor circuit. Thanks