O2 sensor problem, or ...?

confringor · 06-23-2009, 07:50 PM

Hello,

I have a 1999 Escort that has had the engine replaced after almost 190K miles. About 1000 miles after the motor swap the Check Engine light came on and my ScanGauge II code reader identified a P1131 trouble code. The engine seems to be a little slow in responding to throttle and doesn't idle smoothly, but at highway cruise speeds everything seems OK, and no major drop in fuel economy.

The information I've come across so far indicates that P1131 is related to fuel mixture or the upstream O2 sensor. This makes sense, as the ScanGauge also indicates an OPEN LOOP fuel system condition the vast majority of the time - which I understand is not as it should be. Occasionally I'll see it revert to CLOSED LOOP, but it doesn't stay there long.

The O2 sensor harness seems to be clean and free of any obvious problem. Is the next step a new sensor, or are there other things to check that might cause these symptoms?

phantom_smack · 06-23-2009, 08:16 PM

Can yo moniter the o2 sensor reading while the engine is running ?

confringor · 06-24-2009, 12:32 PM

Quote:

Originally Posted by phantom_smack

Can yo moniter the o2 sensor reading while the engine is running ?

Hey, it turns out that I can.

I programmed the ScanGauge to show data from "Bank 1 Sensor 1" and "Bank 1 Sensor 2". As far as I can tell from the Haynes manual the car has only two sensors... so I'm assuming that's them, even though there were instructions for reading sensors 1-4 in each of two banks.

The data read out is simply an integer value between 0-99. Sensor 2 seems to be working (that is, the data values are changing in a way that makes some sense given engine speed and loading). Sensor 1 has so far displayed nothing but 0. I haven't seen it fall back into CLOSED LOOP since I've been monitoring that data, so I don't know if Sensor 1 might display a valid value in that state. If it does, that would seem to indicate an intermittent failure to get data from that sensor. I wonder if that's more likely to be a problem with the sensor, or with the wiring?

Thanks for the suggestion!