P0141 Code

[2000oldsilh]

I have P0141 code. Oxygen sensor (downstream). Which one is it? Is it the one in the exhaust manifold or behind the catalytic converter.

Thanks,

[merc81]

This is NOT the oxygen sensor downstream, it indicates the heater function of the O2 sensor is not correct. Heated O2 sensors respond faster than nonheated types so the pcm measures the time needed by the O2 sensor to come online since engine startup. The test runs only once during each startup/run cycle and it includes all kinds of sensors in the engine as well. The O2 senser we are talking about is the one downstream, past the catalytic converter.

The P0141 code will set when:
No active TP sensor, EVAP system, misfire, IAT sensor, MAP sensor, fuel trim, fuel injector, EGR pintle position, ECT sensor, CKP sensor, or MAF sensor DTCs are present,
IAT is less then 95 degrees (intake air temp),
engine coolant temp and intake air temp are withing 11degrees of each other,
mass air flow is low, below 20gm/s (idle),

Heater O2 signal voltage remains below 150mv of bias voltage longer than it should (more than up to 185 seconds).

Please note that when the O2 sensor goes bad, code P0140 will set, not P0141 and that is due to no signal changes coming from the sensor. Looking at the freeze frame data will help determine the cause for the DTC. Replacing the O2 sensor/heater package may not solve the problem. You need to determine the reason for the heater to show its not working. It could be the cable harness.
John