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P0136 - Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)


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CEL came on while driving this afternoon. Scanned and it came up as P0136 Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2). I have a new OE O2 sensor that I can swap but it appears this is a CIRCUIT issue, not a cat below efficiency or a O2 sensor failure, per se.

 

So, folks, talk to me about what to do. Is this the first or second cat? Should I check the wires going from that cat up to the wiring harness? Should I pull out the O2 sensor and clean it off? Your ideas are welcome.

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Bank 1 refers to the side of the engine with cylinder #1 so that would be the right side. Sensor 2 is after the first CAT I believe. If the signal wire from the sensor to the ECU doesn't have a short to ground on it and the resistance of the wire connection is within specs then the sensor is most likely the trouble.

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  • 4 weeks later...
Alright. I replaced the O2 sensor with OE sensor last week and cleared the code. Gas mileage came back. All seemed to be well until I filled up again and the CEL came back on, complaining of the same code.

 

Any ideas?

 

Disconnect the neg batt lead and press the brake pedal to drain any residual current, then re-connect the neg batt lead or skip these steps and clear the code with your scantool and see how long before the CEL re-appears. If it re-appears quickly, check the circuit wiring for shorts. If no shorts are found, check for exhaust leaks before the secondary bank 1 O2 sensor. A leak before the O2 sensor could cause the sensor to read too lean which could trigger a "low voltage" code.

 

My best guess is that you have an exhaust leak before the CEL throwing sensor.

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So I went to the independent muffler shop across the road and they found a leak coming from one of the flanged on the passenger's side right before the converter. They cut out the flange and put on a metal pipe and welded it on, for $50. The hiss is gone and the car actually seems more responsive now.

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another test you could would be a voltage drop test. that requires the circuit be powered in example the engine running. you then put the volt meter on voltage dc and put one of the leads either neg or pos on the wire as close to the sensor or the ecu (depending where you start, the o2, or the ecu) and then a few feet away on the same wire you put the other lead on it. you should not get more than a half volt at any spot and if you do then you know that is the spot causing the voltage drop.

 

example if this is your wire:

step 1

 

 

o2 sensor here:X--x----------x-------------[clip]-------------------------------------X < ecu

one of the lowercase x's = one of your voltmeter leads

 

step 2

 

02:X-----------x--------------x-[clip]--------------------------------------X < ecu

 

then keep moving down the wire and when you get to a plug in or clip be sure to check it with one lead on each side of the clip and if you get more than a half volt then replace that section of the wire or that particular clip. the goal for this test is .5v or less. say for example you test the clip and you get a 2v reading on your voltmeter that means your sensor would only be receiving 10v instead of 12v. keep in mind that the voltage drops are cumulative so if you have two or three spots that average 1.5v then that is 3 or 4.5v less for the circuit to receive. remember THE CIRCUIT HAS TO BE POWERED for this test to work. LOL you wouldn't believe how many times i would start a voltage drop test with the power turned off only to realize it and then start over.

 

not trying to insult anyones intelligence here, it's just confusing (at least for me) without a visual reference of some sort.

 

if anyone knows this technique better or if i forgot something correct me so i can learn it too.

Edited by SubaruAlliance
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