I am getting a: P0138 O2 Sensor High Voltage (Bank 1 Sensor 2)

what causes a high voltage? I hate to replace a $50-100 sensor if the sensor isnt the problem. Any ideas on this trouble code? Comes on after driving a short time and stays on. I reset, comes on again after a little while. any help appreciated. Thanks.

Devin

 

Iirc, the o2 sensor is on its way out and that's why you are getting varied voltage spikes causing the error code.

 

There are some sites that tell how to check sensor operation. Try searching the web for "Testing O2 sensors on the workbench".

 

Also, check out http://maxima.theowensfamily.com/tsb/NTB02-051a.pdf. It's for 2000 maxima's, but the pictures should still be helpful. oxygensensors.com sells replacement sensors, the cheapest ones are the universal ones that you splice into your existing connector (instructions are on their site). I just replaced mine that way.

 

yea your o2 varies its voltage up and down over .450v. the lower the volts, the leaner it is. the higher the voltage the richer it is. its not that common for o2 sensors to fail in the rich. but it does happen. usually they fail lean. so in your case, the o2 sensor says "Hey, ive got too much fuel!, ECU more Air Please!" so you probably havent had any gas milage issues.

 

Where is the Bank 1 sensor 2 located on the 98 max? is this the one underneith the car by the catalitic convertor? or is it under the hood?

Devin

 

From the stickies:
P0138 = DTC 0510

0510
Diagnostic Trouble Code 0510 points to a problem with the Rear Heated Oxygen Sensor. This sensor is mounted in the exhaust stream, just downstream of the Catalytic Converter. When the two Front Heated Oxygen Sensors are operating properly the Rear Heated Oxygen Sensor is not used for engine control operation. It is used to monitor the condition of the Catalytic Converter. If either or both Front Sensors fail the Engine Control Module uses the signal from the Rear Sensor to maintain a correct fuel/air mixture.

DTC 0510 is detected when the signal from the Rear Heated Oxygen Sensor does not reach the expected maximum voltage threshold value. The possible causes include ...
- Harness or connectors (the sensor circuit is open or shorted.)
- Rear Heated Oxygen Sensor
- Fuel pressure
- Fuel injectors
- Intake air leaks