I have this ongoing issue with the "check engine" light in the instrument cluster coming on at partial throttle. Tromp on the gas pedal, the light goes out. Release the gas pedal, the light goes out. It only comes on at partial throttle. Code (13) indicates O2 sensor, but there are no symptoms that would indicate it is malfunctioning. It runs fine, accelerates fine, no hiccups and the sensor's less than a year old. The handy Haynes manual has that asterix that says Code 13 may or may not be the O2 sensor, but no pointers as what the problem might be if the sensor is good. Is there any way to test the O2 sensor short of buying a new one. And what else could cause a Code 13?

There are ways to bench test it with a propane torch and a fluke meter but if you have gone that far you may as well put a new one in and be done with it.

the Helm gives a little more detail on code 13:



when you replaced the sensor did you use a universal one that required cutting & splicing the harness? maybe a bad connection there... I frequently see "sensor safe" designation on silicone gasket goo - any chance you did some work using other stuff that could have fouled the sensor?

I ran down the mental list, only the valve cover gasket was replaced and I didn't use any sealant. Sensor was a bosch and didn't require splicing
a different plug to match the socket. It was a match straight out of the box. No work on the harness either. I guess I'll just break down and buy a new O2 sensor. I did use a carb spray to clean out the throttle plates.
Said it was safe for O2 on the can, but maybe some of the crud that came off the plates wasn't. Problem didn't show up until weeks after though. Funny thing is the code is intermittent. Mostly happens on extended hi-way driving when the trottle is held steady. I was mostly curious about the function of the O2 sensor. I'm assuming that with only one wire, that the signal is voltage to ground so a bad ground at the threads or the wye pipe would read the same as a bad sensor? I'm guessing. Thanks for the feedback though. I'll go over the harness and connections again.

have you switrched the screws on the back of the cluster yet if not here are the scrwes the light is set to come on at 80000 miles so try chaning the screws it might just be the issue

O2 light is fine. I learned how to do that (after getting tired of the electrical tape falling off the plastic) a few 100,000 miles ago. It's the "check engine" light that's doing the flashing.

You could get a digital multimeter and run a lead down there to measure resistance over the sensor. I believe the resistance should hover around .5 ohms. (see note 1 below)

Connect one lead in line with the sensor wire, and the other to the immediate ground. You might have to get creative with establishing ground.

If you go driving and have it set up while driving and the reading stays almost constant, then the sensor could be bad, or you know it's not getting any power.

I am not sure exactly what the o2 sensor will hover around, maybe it is 5v or .5v rather than resistance (ohms). I do know that an analog multi is not accurate enough to measure the resistance/voltage though.