I have a 2002 Camry V6 with 149,000 miles. My check engine light is on. The code is P1135 Bank1 Sensor1. I purchased an Upstream O2 sensor (Bosch) from AutoZone and changed the front one (right behind the fan) and reset the code. The check engine light went off for a brief moment. But, after a few second the light came back on. I went back to AutoZone, and the sales person told me that often both sensors go bad and suggested I change the rear Upstream O2 sensor as well, which cost another $130. I wanted to see if that's truly the problem and should I go ahead and change it. Please help. Thanks.

  • I had a broken flex pipe before the catalytic converter. Then I blew a rear spark plug. It is a 2002 camry xle v6. I replaced the exhaust system from the manifolds back and still had etc 1135, 420 + 430. First I replaced the O2 sensors and all codes cleared. The engine runs very smoothly and quietly. I have a new air fuel ratio sensor which I may not install if the CEL does not turn on again.
    – Pippo
    Oct 7, 2017 at 1:53

5 Answers 5


You may need to have your computer "un-learn" the old O2 sensor. Unplug the battery for about 30 minutes. This will reset your computer back to factory, where it will then have to relearn the new O2 sensor and might alleviate the situation. You will probably not know for several warm-up cycles if this actual solves the issue for you.

Also, did you double check to ensure you received the correct O2 sensor? Another thought is that the new O2 sensor might be bad. It would not be the first time this has happened. Here is what the code for P1135 is telling you (from Engine-Codes.com):

Possible causes - Faulty Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 - Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 harness is open or shorted - Air-Fuel Ratio (A/F) Sensor Bank 1 Sensor 1 circuit poor electrical connection - Faulty Engine Control Module (ECM) Help with Possible causes What does this mean? When is the code detected? The P1135 is set when the Engine Control Module (ECM) detects a heated oxygen sensor heater circuit malfunction Possible symptoms - Engine Light ON (or Service Engine Soon Warning Light) P1135 Toyota Description

Air-Fuel Ratio (A/F)sensor need to reach a minimum operating temperature of 1200 degrees F to produce an accurate voltage signal. The faster the air-fuel ratio sensor reaches that temperature the faster the sensor will start sending an accurate signal to the Engine Control Module (ECM).

In order to achieve the require temperature, a heater element is included inside the air-fuel ratio sensor. The ECM controls the air-fuel ratio sensor heater element based on signals from the engine coolant temperature and engine load. The ECM controls the heater element circuit by allowing current flow to ground.

The ECM monitors the voltage signal received through the heater element circuit and determines the state of the circuit by comparing the voltage detected with the factory specifications.

  • I'd like to point out that you're not really unlearning a sensor it's resetting the stored fuel trims and other stored values.
    – Ben
    Mar 1, 2016 at 22:35

The error code mentioned that heater part of the O2 sensor is bad. So it is easy to just check it with ohm meter before changing it. You should read below 20 Ohms on this element. Two of the wires are for element and another two for sensor. Do not connect Ohmmeter to the sensor because you may damage it depending to your Ohmeter.


bank one sensor one is the upstream sensor on the back side near the firewall not the front one near the fan. I also made this mistake. although if you had changed both you would have fixed the problem by coincident.


You changed the wrong one to begin with. Should have changed the one at firewall. That is bank1 sensor1. Bank2 sensor1 is by radiator.


If you did any work on the intake, double check the ground connection on the back. Loose nut can throw a p1135 AND 1150. Happened to me, but I unfortunately bought new sensors before checking this.

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