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2003
Chevy Tahoe - P0135 O2 Sensor OBD Code
Question
My engine light came on and I had the code checked and it came up the the O2
sensor(s) were bad. I replaced a 4 of the, checked the 4 fuses in the fuse box
and the engine light still is on and I still get the P0135 code. What is wrong???
Thanks
Vehicle: 2003 Chevrolet Tahoe 5.3L V8 4WD
Codes: P0135 (o2 sensors)
Larry from Marietta, GA
Answer
Hi Larry. First off let me explain the code on your Chevy Tahoe. A P0135 code is O2 Sensor Circuit Malfunction (Bank 1, Sensor 1). Basically that means that there is a problem with the wiring and/or connectors leading to the O2 oxygen sensor on Bank 1 (driver's side for your vehicle and engine) in front of the catalytic converter, or the O2 sensor's heater has failed. You stated the fuses are good, those are another potential cause of this P0135 DTC code.
So, you're definitely on the right track! You didn't say how many miles were on your truck. On average a 2003 vehicle in 2009 would have around 75,000, so I'll assume that figure. It is a good idea to replace all the O2 sensors at the same time if the vehicle's mileage is higher, although you can get away with just replacing the one failed sensor.
In this case you did the right thing, you replaced the affected sensor. You didn't mention if you specifically cleared the code after you replaced the sensors. If you didn't do that, I would suggest you do that next. If you have and the code came back, I would first check the wiring and connectors leading to that O2 sensor. If it's an OEM sensor it should have been a plug-in replacement. If it wasn't you may have had to splice the wires into the existing wiring harness on the car. In that case, double check that all the wires are connected properly. Also, disconnect the sensor and use a ohm meter (or DVOM) to measure the resistance of the heater circuit wires. Check the resistance of the "bad" sensor with the one on Bank 2 which should be "good". If the resistance is not within spec then the O2 sensor needs to be replaced (again).
Good luck with your Tahoe O2 sensor problem!
See also: P0135 trouble code at OBD-Codes.com