Temperature sensor

[GPFred]

As many of you know, I have had an on going issue with a low voltage signal to the O2 sensor bank 1 on my 2000 GP 3.1. Recently the dealer replaced the plug from the MAF and did a rewire between the MAF, PCM, and the O2 sensor. This was their last option and are now stumped. They stopped charging me for the repair when they charged me for the PCM and CAT replacement that I said was not needed. Anyway, can the temperature sensor be bad in that it could send an incorrect reading to the PCM without setting off the SES light. What I am getting at is the dealer says the O2 sensor set the low voltage signal when it recieved an open circuit signal indicating the engine was not at operating temperature and running cold when the opposite was true. This low voltage code always gets set after the car is at operating termperature and upon hard acceleration. When the code gets set and the open circuit is occurring, more fuel is being pumped in to the engine so that it bogs down until you back off the accelerator and then the engine picks up, i.e. flooding seems to be occurring. This car has had the intake redone, fuel injectors replaced, the MAF replaced, the CAT replaced, the PCM replaced, and 6 new O2 sensors, along with wiring replaced.

[GTP Dad]

It is possible that the sensor is bad and sending an incorrect signal. It is inexpensive to replace so I would try it. Also the intake air sensor may be bad as well. This can do the same thing as the water temp sensor especially if it is sending an incorrect air temp reading to the PCM. I would change both.

[GregA]

Originally Posted by GPFred

... Anyway, can the temperature sensor be bad in that it could send an incorrect reading to the PCM without setting off the SES light.

If you are talking about the Engine Coolant Temperature (ECT), Yes. The temperature can appear to be "out of range" and not turn on the SES light. On my car (van actually), this sometimes happens and a "history code" is stored, but no light.

Originally Posted by GPFred

What I am getting at is the dealer says the O2 sensor set the low voltage signal when it recieved an open circuit signal indicating the engine was not at operating temperature and running cold when the opposite was true. This low voltage code always gets set after the car is at operating termperature and upon hard acceleration. When the code gets set and the open circuit is occurring

I missed your other posts. What are the codes that are coming up.

Also, is that really "open circuit" or "open loop"?

[GPFred]

The code that is recurring is P0131 - low voltage bank 1 sensor 1. As to the open circuit, I should have said "open loop". I will probably replace the ECT and the Intake air sensor. I don't know what else to do at this point. I'm sure the dealership doesn't want to see the car again. The last time I was in, we joked about setting it afire and rolling it in to the ditch out behind the dealership. But seriously, the dealer is at a loss now.

[richtazz]

I agree with GTP Dad, that you should change both the CTS and IAT sensors. If that doesn't help, the TPS (throttle position sensor) may also be borderline and causing and incorrect fuel mixture calculation at or near WOT during hard acceleration.

[BNaylor]

Ah, the ongoing GPFred saga.

Before replacing parts needlessly and adding them to your "did not fix" list I'd do some relevant and better troubleshooting concentrating on why you are getting the P0131 DTC (HO2S Circuit Low Voltage Sensor 1). The ECT, IAT and TPS are possible but I would surprised they are the cause but I guess there is always a first.

The reason why the bogging is occurring is you are most likely running in "fuel enrichment mode". In others words a lean trim condition. That is a major condition for DTC P0131 to set and the condition must be present for at least 15 seconds. Another major parameter is the O2 sensor signal voltage is remaining at less than 300 mV during closed loop operation. If the PCM is, in fact, switching between open and closed loop mode the sensors mentioned are probably working properly. You can check the calibration of the IAT and ECT with a DMM. Both use the same temperature/resistance charts. The TPS output can be checked for proper output at idle, WOT and in between for linearity. (4.0 vdc idle to 4.5 vdc WOT). The PCM provides a 5 volt reference signal to the input of each. Your ECT aka CTS also supplies the engine temperature gauge at the IP Cluster so check that for any anomally.

Did you or the mechanics ever check fuel pressure for proper specs and engine vacuum at the throttle body and one of the vacuum ports at the upper intake manifold? Both of these could cause the DTC. Also, monitoring the output of the 02 sensor (purple wire) looking for proper voltages and whether in range can be revealing.


ECT and IAT Calibration Chart 3100/3400/3800