Question about 1999 GMC Jimmy

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1999 GMC Jimmy SLT Engine light is staying on. Jimy was surging. losing power and regaining - unable to maintan speed. Dealer replaced mass air flow sensor with change up sensor and cleared DTC'S. Road tested foun sluggish. Surging rendered vehicle undriveable returned to dealer who then replaced transmission. Vehicle began surging again returned to dealer beleives the problem to be the alternator which is 3 mos. old.

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  • dforde202 Mar 18, 2011

    I appreciate all the help I can get with this problem. The dealership is Sherwood Chevrolet in Saskatoon, SK. so they are supposed to be experts w/GM products. The 2 codes were P0101 and P1875........this code was supposed to be likely due to Mode Switch. Which is????? Invoice says: Scanned for DTC's in PCM - has none. Road test showed Trans does not shift and is slipping. Does not shift into 4WD. Trans need replacing.

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  • GMC Master
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What kind of a dealer are you going to . If what you are saying is correct the MIL light is on then what you need to do is find out what code is making the light come on it will have a # P0 - - - the MAF or mass air flow sensor on this vehicle would be P0102 or P0103 its the first sensor and a main sensor that would create a lot of driveably problems but the code would be there . How the dealer got from the maf to replaceing the transmission and ovesely that was not the problem and now it telling you you need a new alternator is eighter criminal or complete incompants. Find out what the code is and i will tell you what is wrong with it and don't go back to that dealer you didn't need any of these parts . Any auto parts store will read these codes at no charge for you this is why the OBD 11 system is there and is standard on all vehicles with a few exceptions in the us but not your vehicle and regulated by the federial goverment . I work on vehicles and owen one a blazer my self witch is the same thing as a jimmy. And you are getting riped off pier_j

Posted on Mar 17, 2011

  • JOHN LAPIER Mar 18, 2011

    P1875 is a low circuit manfunction in the 4 wheel drive shifting system . I don't completely understand what you are saying about transmission slip but the transmission opperatre bolth with electrical and vacuum and the 4 wheel drive regardless if you have the electrioic shift or manual shift opperates on vacuum .So this sounds like a vacuum problem to me because it effects the 4 wheel and the transmission as well as if you have vacuum leaks the engine is going to run poorly and all 3 of these things seam to be happening at the same time . Tell me more about this thing dose and i hope you didn't have to pay for a new transmission

  • dforde202 Mar 19, 2011

    Yes, unfortunately I did have to pay for a new transmission. Before that I paid for a new Mass Air Flow Sensor replacement with change up sensor (whatever that means). Neither of these fixes cured the problem of vehicle surging - not being able to maintain a speed of mor than 40kms/hr tach

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  • GMC Master
  • 8,206 Answers

Hi, as we discussed on the chat, there are three possible causes in my mind. One would be a cut in the intake hose between the MAF sensor and the throttle body. This could have caused the P0101 and made the dealer change the MAF sensor. If they didn't notice a **** in the hose--voila, the problem persists. If, on the other hand, you have a new code that indicates the TPS or the MAP sensor, that indicates a totally different repair. The code will help us narrow it down to where we have a lot less work to diagnose--let's take advantage of the computer.
I will be out working tomorrow, but I will check in as often as I can.

Posted on Mar 17, 2011

  • 1 more comment 
  • Jeff Turcotte
    Jeff Turcotte Mar 18, 2011

    OK, so they are saying there are no codes and yet the engine light is on? How do they explain that? If the engine light is on, there has to be a reason. I mean the light wire could be shorted, but whatever--there is a reason they should be looking for--and not the alternator (unless the alternator is not charging).

    Now, if we are stuck with no codes and the engine still surging, I would be testing the MAP and TPS sensors for proper signals. Let me look up test procedures and add them here.

  • Jeff Turcotte
    Jeff Turcotte Mar 18, 2011

    MAP sensor tests:




    Fig. Fig. 1: Typical Manifold Absolute Pressure (MAP) sensor wiring diagram (wire color, terminal identification/location may vary on certain models)



    1. Backprobe with a high impedance voltmeter at MAP sensor terminals A and C .

    2. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.

    3. If the voltage is not as specified, either the wiring to the MAP sensor or the VCM may be faulty. Correct any wiring or VCM faults before continuing test.

    4. Backprobe with the high impedance voltmeter at MAP sensor terminals B and A .

    5. Verify that the sensor voltage is approximately 0.5 volts with the engine not running (at sea level).

    6. Record MAP sensor voltage with the key ON and engine off.

    7. Start the vehicle.

    8. Verify that the sensor voltage is greater than 1.5 volts (above the recorded reading) at idle.

    9. Verify that the sensor voltage increases to approximately 4.5. volts (above the recorded reading) at Wide Open Throttle (WOT).

    10. If the sensor voltage is as specified, the sensor is functioning properly.

    11. If the sensor voltage is not as specified, check the sensor and the sensor vacuum source for a leak or a restriction. If no leaks or restrictions are found, the sensor may be defective and should be replaced.




    Fig. Fig. 2: Using jumper wires and a high impedance voltmeter test between MAP sensor terminals A and C with the key ON and engine off. The voltage should be approximately 5 volts










    Fig. Fig. 3: Next test between MAP sensor terminals A and B with the key ON and engine off. The voltage should be approximately 0.5 volts







    Fig. Fig. 4: Manifold Absolute Pressure (MAP) sensor location-1996 4.3L engine shown, others similar




  • Jeff Turcotte
    Jeff Turcotte Mar 18, 2011

    TPS tests. The TPS is mounted to the side of the throttle body where air enters the engine.



    OPERATION


    The Throttle Position Sensor (TPS) is connected to the throttle shaft on the throttle body. It is a potentiometer with one end connected to 5 volts from the VCM and the other to ground. A third wire is connected to the VCM to measure the voltage from the TPS. As the throttle valve angle is changed (accelerator pedal moved), the output of the TPS also changes. At a closed throttle position, the output of the TPS is low (approximately 0.5 volts). As the throttle valve opens, the output increases so that, at wide-open throttle, the output voltage should be approximately 4.5 volts. By monitoring the output voltage from the TPS, the VCM can determine fuel delivery based on throttle valve angle (driver demand).



    TESTING


    See Figures 1, 2 and 3



    1. Backprobe with a high impedance voltmeter at TPS ground terminal and 5 volt reference signal terminal.

    2. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.

    3. If the voltage is not as specified, either the wiring to the TPS or the VCM may be faulty. Correct any wiring or VCM faults before continuing test.

    4. Backprobe with a high impedance voltmeter at the TP signal terminal and the sensor ground terminal.

    5. With the key ON and engine off and the throttle closed, the TPS voltage should be approximately 0.5-1.2 volts.

    6. Verify that the TPS voltage increases or decreases smoothly as the throttle is opened or closed. Make sure to open and close the throttle very slowly in order to detect any abnormalities in the TPS voltage reading.

    7. If the sensor voltage is not as specified, replace the sensor.




    Fig. Fig. 1: Common Throttle Position Sensor (TPS) wiring diagram (wire color, terminal identification/location may vary on certain models)








    Fig. Fig. 2: Using jumper wires and high impedance voltmeter, test between the sensor ground and reference terminals, the voltage should be approximately 5 volts







    Fig. Fig. 3: Next test between the sensor signal and ground terminals, verify that the TPS voltage increases or decreases smoothly as the throttle is opened or closed




    REMOVAL & INSTALLATION

    Except 1998-99 2.2L Engines


    See Figure 4





    Fig. Fig. 4: Common Throttle Position Sensor (TPS)

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