Contour Enthusiasts Group Archives Forums General Troubleshooting O2 sensors dropping like flies.

My car had the check engine light on for an 02 sensor. It was showing the downstream sensor in bank too. I changed it, and two days later it came on for the first sensor in bank 2. I changed it, it passed emissions for PA, then on the way home the CEL came on again. This time for the first sensor in bank 1. Is there something else going on here, or are they just all wearing out? Each sensor is showing codes such as P1131 and P1151.

Did you disconnect the battery for 5 minutes after you did all this?

Bob

I cleared the codes with a scantool.

You need to disconnect the negative battery cable for 5 minutes like he said, it resets the PCM.

he doesn't need to disconnect anything when using a scan tool..

car running very rich at all?...miles?.. its not as unusual as u may think.

Hitman, Hitman, Hitman will u ever learn?


Back to the original question:
P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1.
P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2.

these codes do not indicate bad HEGO necessarily, could it be that you actually are running lean due to something else? like a leak or bad fuel pump?

Yes, the car does seem to run rich. People say im blowing out black smoke when I pull out from a stopsign.

not according to the codes, you don't. now, that you have a known good sensor on bank 2, can you see the readings on that one? I know I can use my scantool to read the HEGO sensor output, can you do the same? bad sensor stuck on lean can cause it to run rich. of course if you run rich because of one sensor, the second one will follow quickly.

P1131 and P1151 are normally worn out upstream (not downstream) sensors.

If you replaced any downstream (after the pre-cat) seansors due to these codes, you wasted your money.

The scantool will clear the codes, but will not clear the fuel trim tables that will keep the mixture either too rich or too lean (depending on the failure mode of the original sensors).

Because of this, it is necessary to disconnect battery power from the computer for a long enough time for the internal keep-alive power to discharge.

Steve

The first code it was giving was for the 2nd 02 sensor in bank two, it was "02 sensor check slow/no response". So I changed it. Next day the upstream came on with P1131.

I'll try pulling the fuses today when I go home from school.

Oh, and I'm just using the scantool at work (autozone) to test the codes. We cant do anything but read/erase codes with that tool, since its one of the very cheap ones.