Error 141 Oxygen sensor relay location?

[Elmer Fudd]

I have had a check engine error code 141 for quite a while now - "Downstream heated 02 sensor heater circuit fault (Bank 1)." It did not clear up after replacing this sensor, located after the catalytic converter. My 4.0L V6 VIN X series pushrod only has the one sensor after the catalytic converter. I tried replacing it again with the same result. I have rigged the old sensor with some test leads to try tomorrow, but I am wondering if the relay that turns on the heater circuit per the Haynes manual could be bad. I can not find any reference to the location this particular relay in the owner's manual or the Haynes manual. Does anyone have any insight on this? Thanks!

 

[budwich]

I don't think that there is a relay per sa. The PCM module has some "switching" in it to pass a ground towards the heaters. You need to check that you are getting both the voltage and the grounds at the o2 sensor in question. My guess is the ground at the PCM (many of them) is not there. Of course, there is equal chance that the wiring is broken.

 

[Elmer Fudd]

Thanks for the reply budwich. I tried the old replacement sensor today, with leads soldered to the four wires. Autozones free diagnostic info on the sensor said the resistance across the heater circuit should be 6 ohms, both the new and old replacement sensors (both Bosch) showed 2 ohms. The Haynes manual said the voltage across the heater circuit should be 10 volts, the actual voltage while running was over 13 volts. I guess this suggests no real resistance, hence no heating? The signal voltage while running was supposed to be between 100 and 400 millivolts, actual was 65.

I had called in a while ago to a radio car repair show after the first replacement sensor did not fix the problem. The host suggested that some of these aftermarket replacement sensors are bad and to try another. Maybe I need to try an OEM sensor?

 

[budwich]

Well... it would "appear maybe" both are bad.... but perhaps not. If the new one is as you say, then you should be able to get them to take it back with the corresponding "bench test" showing them the resistance condition.

I recently replaced both of mine and could probably tested the old one(s) to see what they say. As for Haynes... all I can say is from the truck CD, the circuit appears to show 13 volts heading towards the heater but it doesn't really show what the PCM switches into the circuit with the ground... a resistor???? The other thing is low resistance is very hard to read with "personnal meters" because they tend not to be calibrated very well and the difference at the low ends is usual very bad.... hence a 1 ohm might look like 5 or a 6 ohm might even look like a short. If you can get a 1% 1 or 2 ohm resistor and see if your meter is "close" just to check things.

 

[Elmer Fudd]

Went to the dealer to get an OEM sensor. $98, or exactly twice what an aftermarket one cost me. They tried to sell me an open package one - it looked used Then I noticed it was stamped Bosch, just liked the two aftermarket ones I have already bought. I put the multimeter that I just happened to have in my pocket on it and the heater resistance read 2 ohms, like the others. I think I'll save my $98, thank you.