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2001 Sentra. MIL/DTC falsely condemn O2S. Why?

I am working on:

2001 Nissan Sentra 1.8 L

The "Service Engine Soon" light comes on repeatedly soon after being reset. The DTC is:

P0154 Oxygen sensor circuit no response detected (Bank 2 sensor 1)

The oxygen sensor is, in fact, capable of switching. It does this rarely, because the fuel control system remains in open loop on bank 2. A new oxygen sensor did not fix the problem. The new sensor switched between low and high as the old one, and about as infrequently.

The weird thing is that the scanner says that the output from the oxygen sensor is a constant 1.275 volts. Or on some occassions it stays at a constant

2.65 volts. The oxygen sensor is not capable of producing so high a voltage. And the Vantage trace shows the real output to be in normal range.

What could be the cause of such a problem? Is 1.275 volts a substituted value? If so, under what conditions does the PCM do substitution?

A couple of other tests. (1) I can disconect the O2S wires and test the voltages on the PCM side of the connector. None of the wires are shorted to

1.275 volts, as seen at the connector.

(2) I can unplug the harness going into the PCM. I find continuity in the signal wire from the O2S connector to the PCM connector. But there is one more weird thing here. The pin number at the PCM is one-off from the pin number specified by SomeData.

So what could cause a good O2S to give a faulty reading at the PCM, as seen from the scanner?

Jim S.

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Reply to
JimS
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Bad connection between the O2 sensor and the ECM.

Reply to
JimV

JimV wrote in news:S76dnb6f-7AL-

3XbnZ2dnUVZ snipped-for-privacy@comcast.com:

maybe a bad O2S ground? Maybe he needs to find the ground screw for that sensor wire and clean under it/install a star washer. maybe a bad crimp on a wire connector.

Reply to
Jim Yanik

Have you checked the O2 sensor heater voltage? On the 1.6 engine it is a constant 300mV. Maybe somehow the heater voltage is getting into the sensor output line. Just a thought. Good luck. Al

Reply to
al

very common, seen this more times than I can count.

What is the production date of the vehicle?

is it between 9 and 10 of 2001 ???

Reply to
NissTech

(2) I can unplug the harness going into the PCM. I find continuity in the signal wire from the O2S connector to the PCM connector.

*****

jyanik>...O2 sensor heater voltage?

One of the wires going into the O2S is about 13V. This tells me that the heater is getting good battery voltage.

jyanik>On the 1.6 engine it is a constant 300mV.

I am not aware of any voltage drops that would be

300mV. Am I missing something?

jyanik>Maybe somehow the heater voltage is getting jyanik>into the sensor output line. Just a thought.

Good thought. But (1) we get the same behavior with both the old and a new O2S. And (2) I never see

1.275 volts on the signal wire coming out of the O2S. I only see 1.275 volts on the scanner. At the O2S signal wire I see nothing be good clean O2S type signal voltages.

*****

NissTech>very common, seen this more times than I NissTech>can count.

I have been hoping to hear from someone with this kind of experience.

NissTech>What is the production date of the vehicle? NissTech>is it between 9 and 10 of 2001 ???

I do not know at this moment but I will find out. (My internet connection is at home and the Nissan is at the shop where I work.)

What if the date is in this range? What else can you tell me about it?

Jim S.

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Reply to
JimS

NissTech>What is the production date of the vehicle? NissTech>is it between 9 and 10 of 2001 ???

The production date is 8/2000.

Jim S.

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Reply to
JimS

jyanik>maybe a bad O2S ground?

All voltage tests at the O2S were done with the DVM or Vantage ground wire connected to the battery ground terminal. And all such voltages look good. While a bad O2S ground would definitely cause problems, that is not the case here.

My test equipment sees good voltages. It is the ECM that thinks the voltages are bad.

Jim S.

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Reply to
JimS

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