Check Engine Light Error Code P0136: Oxygen Sensor Circuit Low Voltage – Bank 1 Sensor 2

Hello All,

My 2005 Toyota Sequoia SR5 check engine light is on. The local auto parts store plugged in their OBD code reader found code P0136. The onboard diagnostic (OBD) code P0136 is defined as an Oxygen Sensor Circuit Low Voltage in Bank 1, Sensor 2. Low voltage. Ok they say good chance the O2 sensor needs to be replaced, so I replaced the sensor, pretty easy, $65. The old sensor I took out looked in pretty good shape. I cleared the code by removing the battery for a few hours.

After 4 or 5 days of driving the light comes back with P0136 again. Dang it!

Caddyman says Common Problems That Trigger the P0130 and P0136 Code:

Ok, that’s great but is there anyway to get a better idea of which of these issues is more likely? Talking to my mechanic and searching the internet I don’t feel anyone knows. Any advice?


Oxygen sensor 2 is after the catalytic converter, and monitors the catalyst efficiency.

Also, sensor 2 is not the same as sensor 1, which is before catalytic converter. So if you install a sensor that’s suppose be located before catalytic converter after the catalytic converter, it’ll send a skewed voltage signal.

So, are you sure you installed the correct O2 sensor after the catalytic converter?


Yes, I’m sure. I can see both sensors. I replaced the one closest to the
muffler/tail pipe.

These vintage Toyota’s tend to be brand sensitive with the oxygen sensors. If you did not install an oe sensor that could be the problem. Denso brand sensors seem to work the best here

Yes I used the Denso, got the part number from my mechanic, looked identical to the original unit, had the factory wire harness.

I suspect the issue is low fuel pressure because at one point the check engine light (CEL) was on then went off after I tightened the gas cap. The CEL came back with P0136 again later. Is there a way to check or eliminate that possibility of low fuel pressure?

You would have to manually check fuel pressure with a gauge to figure that out, I would suspect that you would have running issues or other codes that point to a lean condition if low fuel pressure were the case. A fuel pressure concern would also effect both the left and right banks of the engine equally so you would end up with a code from the other downstream oxygen sensor. The key here is going to be checking fuel trim data and watching the voltage readings the sensor is giving. You may need to consult your mechanic so it can be hooked up to a scan tool

Good point. I guess I’ll have to take it in. Bummer. I’ll report back the
results. Thanks for your help!

Re-read Tester’s post. You confirmed you replaced the one in the correct position. He’s asking if you’re sure you used the correct sensor for that position. According to Tester, they are not the same and have no reason to doubt his authority on the subject.

Yes, I confirmed the sensor position and part number.

My mechanic hooked it up to his scan tool and reported that both the left and right downstream sensors are “flat lined”, unresponsive. He said that either there is failed sensor wiring, circuit problem or defective PCM.