PCM or ECM – Which one is it and how do I test it?

New Topics Forums General Discussion 1993 – 1998 Nissan Quest PCM or ECM – Which one is it and how do I test it?

This topic contains 4 replies, has 3 voices, and was last updated by  1castillo 5 years, 8 months ago.

Viewing 5 posts - 1 through 5 (of 5 total)
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  • #1095

    gagosto209
    Member

    Hello Everyone!

    I have a 1996 Nissan Quest that has a Check Engine light on. The engine hesitates with speed and power badly. I’ve exhausted all of resources, so I’m posting this question in hopes that I’ll find a solution to my problem. My “boiling point” is reaching its top level and if I don’t find a solution – this minivan won’t be my quest much longer.

    I took the quest to Autozone and Advance Auto for a “check engine” light diagnostics. They both told me the computer was reporting a knock and TPS sensor. I purchased both sensors (yes, I’m aware of the difficulty in changing the knock sensor). We’ll get to that later if I need it.

    So, I replaced the TPS sensor. After replacing the TPS sensor, I wanted to check the voltage of the TPS connector (just to make sure the sensor is getting voltage). As crazy as this sounds, when I connect the multimeter probes into the TPS connector, I get zero (flat line) readings. I’m inserting the positive probe of the voltmeter on the REF terminal and the negative probe into the GND terminal. I should get a reading of 5.0 volts. The odd thing is that if I connect the negative probe into the REF and the positive into the GND terminal, I get a reading of 10.7 I’ve double checked my work and when testing the voltage properly as described in the haynes manual, I get zero readings.

    According to the haynes manual, if reference voltage is not available, I may have a open circuit to the PCM or a defective PCM. I’m assuming a PCM is the ECU, since the haynes manual does not reference anything about a ECU. If I’m wrong, please correct me.

    Here’s my main question, how do I test a PCM/ECU? I either have a problem with the wire harness or the PCM/ECU. I would like to play the process of elimination here. Does anyone know of a way to test the PCM/ECU without actually removing the PCM/ECU? And if so, could you please describe how to test it?

    I know that a million other things could cause engine hesitations and check engine lights, but I need to rule out the possibility of having a bad/defective PCM/ECU before I can proceed with other diagnostics.

    Thanks a million to anyone that can help with this,

    Gabriel

    #4407

    gagosto209
    Member

    Also, does anyone know if I need to take a trip to the dealership to have them reprogram the ECU? (if and when I do replace it)

    Sometimes you need to — other times you don’t…depending on the vehicle and ECU and I’m not quite sure if its required for this particular vehicle and year.

    thanks again

    #5514

    1castillo
    Participant

    I just happen to be on same boat has you, my 94 quest runs bad at idle and my pcm to tps voltage is 2.5 volts but I dont know if the pcm is bad. What was your fix? Thanks in advace on the replay.

    #5518

    Astroalcher
    Participant

    Do not change the knock sensor , don’t bother with it .

    The computer rarely goes wrong .

    Tell me what code you are getting on the cel.
    The TPS can be defective ,, is it a Hitachi ?
    Nissan has the best TPS a Hitachi .
    Clean the connector on the harness side with DE-Oxit .

    Did you clean up the MAF first ??
    Ask me if you don’t know how to clean it .
    alcher@rogers.com

    Did you check for a vacuum leak ??

    Astroalcher

    Hello Everyone!

    I have a 1996 Nissan Quest that has a Check Engine light on. The engine hesitates with speed and power badly. I’ve exhausted all of resources, so I’m posting this question in hopes that I’ll find a solution to my problem. My “boiling point” is reaching its top level and if I don’t find a solution – this minivan won’t be my quest much longer.

    I took the quest to Autozone and Advance Auto for a “check engine” light diagnostics. They both told me the computer was reporting a knock and TPS sensor. I purchased both sensors (yes, I’m aware of the difficulty in changing the knock sensor). We’ll get to that later if I need it.

    So, I replaced the TPS sensor. After replacing the TPS sensor, I wanted to check the voltage of the TPS connector (just to make sure the sensor is getting voltage). As crazy as this sounds, when I connect the multimeter probes into the TPS connector, I get zero (flat line) readings. I’m inserting the positive probe of the voltmeter on the REF terminal and the negative probe into the GND terminal. I should get a reading of 5.0 volts. The odd thing is that if I connect the negative probe into the REF and the positive into the GND terminal, I get a reading of 10.7 I’ve double checked my work and when testing the voltage properly as described in the haynes manual, I get zero readings.

    According to the haynes manual, if reference voltage is not available, I may have a open circuit to the PCM or a defective PCM. I’m assuming a PCM is the ECU, since the haynes manual does not reference anything about a ECU. If I’m wrong, please correct me.

    Here’s my main question, how do I test a PCM/ECU? I either have a problem with the wire harness or the PCM/ECU. I would like to play the process of elimination here. Does anyone know of a way to test the PCM/ECU without actually removing the PCM/ECU? And if so, could you please describe how to test it?

    I know that a million other things could cause engine hesitations and check engine lights, but I need to rule out the possibility of having a bad/defective PCM/ECU before I can proceed with other diagnostics.

    Thanks a million to anyone that can help with this,

    Gabriel

    Rear lock of sliding door – Ho

    Lubricate it first and then tell me the symptoms.

    Astroalcher
    Vitally

    #5554

    1castillo
    Participant

    Hello, thanks 4 the response

    I don’t have any codes., the only problem I have spotted is the low voltage from the TPS connection to the ECU. I get 2.5v out of the 5v required.

    Quest symptoms, runs bad at idle under 1500 rpm and dies(runs good with little gas over the 1500 rpm mark).

    Things I have tested:
    Back probe MAF sensor tested (GooD)
    Tested IAC valve (GOOD)
    Gas pressure (GOOD)
    Battery voltage (GOOD)
    Fuel Injector spraying (good)
    Spark plug wires (good)
    distributor and components (good)
    power transistor (good)
    Ignition coil (good)
    TPS (good)
    CTPS (Good)

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