Here is the situation:

I have a 2000 Toyota Camry V6 (not California model) with a reoccurring check engine light. The code is P0135 - Heated Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

I have had the oxygen sensor replaced. I also replaced the battery just in case that was the issue since it was 4+ years old anyways. After the same code came back one month after the O2 sensor replacement, I took it back to the mechanic who said he checked with voltages and resistance on the wiring and everything looked good. He said according to the service manual, the next step would be to replace the engine computer but that wouldn't be necessary. I could just drive the car with the light on since he verified the sensor and wiring are fine. From what I have read though, a bad engine computer is pretty unlikely.

The light now comes on every 2 days after I keep resetting it. I obtained an OBD reader that reads live data and can see that the O2 sensors are oscillating between 0.9v and 0.1v which is normal. The vehicle also goes to closed loop status quickly after start up indicating that the oxygen sensor heater is working at least most of the time. I've read in the service manual that when this code trips, the only thing that happens is that the computer turns off the heater circuit. The heater circuit will come back on after the ignition turns off and back on the next time the car is started and continue to operate until the code trips again.

My question is two-fold:

  1. Is there any other simple fixes to try here?
  2. Can I safely ignore this problem since it seems that the o2 sensors are operating normally in a closed loop? One concern is that the TRAC OFF light also comes on with the check engine light which means that the car is now operating without traction control which in theory means it is less safe to drive.

This car is old (although only has 110K miles on it) and I have already spent a decent amount of money trying to get this fixed so I am reluctant to spend any more money on it. Also, I watched this youtube video - https://www.youtube.com/watch?v=rWoEIEAql2I

This seems like the kind of troubleshooting needed to address this issue and realistically, I can't do this myself nor afford to pay a mechanic to do it.


  • Welcome to Motor Vehicle Maintenance & Repair! The problem with your diagnosis is, it's the heater circuit, not the O2 sensor itself, which is bad. You will continue to see the up/down cycle of the O2 voltages, but it will be slow to warm up since it's the heater circuit (IOW: Your mechanic isn't lying to you ... it should work just fine.) Ensure you're checking the correct circuit wiring. You may also check to ensure the fuses for the O2 heaters are seated without any corrosion on them. That's just a thought, though. The fact it comes back after two days sounds right. Takes that long to read. – Pᴀᴜʟsᴛᴇʀ2 Sep 10 '19 at 21:05

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