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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 231 (Engine Controls - 3.9L - DTC P0442 To P2A01) >> DTC P2120, P2122, P2123, P2125, P2127, P2128 or P2138 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal harness connector.
  3. With the ignition ON and the engine OFF, observe the APP Sensor 1 and APP Sensor 2 parameters on the scan tool. The voltage should be less than 0.1 volt.
    • If the voltage is more than 0.1 volt, test the affected signal circuit for a short to voltage or a faulty ECM.
  4. Measure for 4.8-5.2 volts between each of the 5-volt reference circuits and the negative terminal of the battery.
    • If the voltage is more than 5.2 volts, test the affected 5-volt reference circuit for a short to voltage or faulty ECM.
    • If the voltage is less than 4.8 volts, test the affected 5-volt reference circuit for an open, short to ground or a faulty ECM.
  5. Install a 3-amp fused jumper wire between the signal circuit and the 5-volt reference circuit of the APP sensor 1. Observe the APP Sensor 1 parameter on the scan tool. The voltage should be more than 4.8 volts.
    • If the voltage is less than 4.8 volts, test the APP sensor 1 signal circuit for an open, a short to ground or a faulty ECM.
  6. Install a 3-amp fused jumper wire between the signal circuit and the 5-volt reference circuit of the APP sensor 2. Observe the APP Sensor 2 parameter on the scan tool. The voltage should be more than 4.8 volts.
    • If the voltage is less than 4.8 volts, test the APP sensor 2 signal circuit for an open, a short to ground or a faulty ECM.
  7. Measure for 4.8-5.2 volts between one of the 5-volt reference circuits and each of the low reference circuits.
    • If the voltage is less than 4.8 volts, test the affected low reference circuit for an open or a faulty ECM.
  8. Turn OFF the ignition.
  9. Disconnect the ECM harness connector and measure the 5-volt reference, the low reference and each of the signal circuits between the ECM and the accelerator pedal for less than 5 ohms.
    • If the resistance is more than 5 ohms, repair the affected circuit.
  10. Test the signal circuits for continuity between them.
    • If continuity exists between the signal circuits, repair the short.
  11. If all circuits test normal, replace the accelerator pedal.
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