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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 228 (Engine Controls - 3.9L - DTC P0011 To P0420) >> DTC P0120, P0122, P0123, P0220, P0222, P0223 or P2135 >> 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 throttle body harness connector.
  3. With the ignition ON and the engine OFF, observe the TP Sensor 1 parameter on the scan tool. The voltage should be less than 0.1 volt.
    • If the voltage is more than 0.1 volt, test the TP sensor 1 signal circuit for a short to voltage or a faulty ECM.
  4. Observe the TP 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 TP sensor 2 signal circuit for a short to ground or a faulty ECM.
  5. Measure for 4.8-5.2 volts between the 5-volt reference circuit and the negative terminal of the battery.
    • If the voltage is more than 5.2 volts, test the 5-volt reference circuit for a short to voltage or faulty ECM.
    • If the voltage is less than 4.8 volts, test the 5-volt reference circuit for an open, 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 TP sensor 1. Observe the TP 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 TP sensor 1 signal circuit for an open, a short to ground or a faulty ECM.
  7. Install a test lamp between the signal circuit of the TP sensor 2 and the negative terminal of the battery. Observe the TP Sensor 2 parameter on the scan tool. The voltage should be less than 0.1 volt.
    • If the voltage is more than 0.1 volt, test the TP sensor 2 signal circuit for an open or a faulty ECM.
    • If test lamp illuminates, test the TP sensor 2 signal circuit for a short to voltage or faulty ECM.
  8. Measure for 4.8-5.2 volts between the 5-volt reference circuit and the low reference circuit.
    • If the voltage is less than 4.8 volts, test the low reference circuit for an open, high resistance or for a faulty ECM.
  9. Turn OFF the ignition.
  10. 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 throttle body for less than 5 ohms.
    • If the resistance is more than 5 ohms, repair the affected circuit.
  11. Test the signal circuits for continuity between them.
    • If continuity exists between the signal circuits, repair the short.
  12. If all circuits test normal, replace the throttle body.
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