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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29450
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I HAVE A 2003 CHEVY TAHOE AND MY CHECK ENGINE LIGHT CAME ON.

Customer Question

I HAVE A 2003 CHEVY TAHOE AND MY CHECK ENGINE LIGHT CAME ON. I WENT TO AUTO ZONE AND THEY CHECKED IT AND TOLD ME THAT I NEEDED TO REPLACE THE O2 SENSOR. I REPLACED IT (THE ONE ON THE PASSENGER SIDE) AND THE LIGHT STILL CAME ON SO I REPLACED THE ONE ON THE DRIVER SIDE AND STILL THE LIGHT STAYS ON AND THE SAME CODE COMES UP SAYING I NEED TO REPLACE THE O2 SENSOR. I CRWALED BACK UNDER THE TAHOE TO CHECK THE WIRES AND NOTICED A "THIRD" SENSOR ON THE PASSENGER SIDE FARTHER BACK. IS THIS ALSO A O2 SENSOR AND SHOULD I ALSO REPLACE THIS ONE AS WELL. SO FAR I HAVE SPENT $100.00 ON SENSORS (2)
Submitted: 7 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 7 years ago.
Welcome. Do you have the code numbers?
Customer: replied 7 years ago.

I THINK IT WAS P1035

Expert:  GM Tech (Cam) replied 7 years ago.
Are you sure it is a P1035? This code is not valid. Perhaps a p0135?
Customer: replied 7 years ago.
YES IT IS P0135, SORRY
Expert:  GM Tech (Cam) replied 7 years ago.

OK. This code sets because of the internal heater of the oxygen sensor is not getting hot. Considering you have replaced the sensors and the issued did not go away, I believe then that you either have a bad wire or perhaps the fuse that feeds the heater circuits is no good. Start by checking all the fuses in the underwood fuse block. The wire at the oxygen sensor is the pink wire and it should have battery power with the key on.

Customer: replied 7 years ago.
WHAT IS THE 3RD SENSOR FARTHER BACK FOR?
Expert:  GM Tech (Cam) replied 7 years ago.
There are actually four sensors. Two on each bank, one to monitor the engine and the other to monitor the catalytic converter.
Customer: replied 7 years ago.
I CHECKED ALL 3, 15 A FUSES UNDER THE HOOD. ALL 3 ARE OK, WHAT NEXT?
Expert:  GM Tech (Cam) replied 7 years ago.

There are four oxygen sensors on the exhaust system on the not three.Object Number: 664828  Size: SH

Object Number: 664951  Size: SH

Customer: replied 7 years ago.
OK SO WHAT SENSORS DO I REPLACE WITH A P0135 CODE. I ALREADY REPLACED THE FRONT TWO AND CHECKED THE FUSES UNDER THE HOOD. 1,2 & 3 ARE FINE.
Expert:  GM Tech (Cam) replied 7 years ago.
In the picture which is sensors did you check?
Customer: replied 7 years ago.
as mentioned before, i replaced the front left and front right. I checked the fuses they (all 3) are OK.
Expert:  GM Tech (Cam) replied 7 years ago.
Ok, then the rear sensors are likely the issue. Check the wiring to the rear sensor.

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