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Home >> Buick >> 2008 >> Allure CXL >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 10 (Engine Control System & Fuel System - 5.3L - DTC P0420 To DTC P3449) >> DTC P2120, P2122, P2123, P2125, P2127, P2128, or P2138 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.
  1. Ignition OFF, disconnect the harness connector at the accelerator pedal. Allow at least 60 seconds for the ECM to power down. This can be verified by a loss of communication message on the scan tool.
  2. Test for less than 5 ohms between each low reference circuit terminals A and D and ground.
    • If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  3. Ignition ON, test for 4.8-5.8 volts between each 5-volt reference circuit terminals C and F and ground.
    • If less than 4.8 volts, test the affected 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
    • If greater than 5.2 volts, test the affected 5-volt reference circuit for short to voltage. If the circuit test normal, replace the ECM.
  4. Ignition ON, verify the scan tool APP sensor 1 and 2 voltages are less than 0.1 volt.
    • If greater than 0.1 volt, test the APP sensor 1 and 2 signal circuits terminals B and E for a short to voltage. If the circuit tests normal, replace the ECM.
  5. Install a 3A fused jumper wire between the signal circuit terminal E and the 5-volt reference circuit terminal F of the APP sensor 1. Verify the scan tool parameter APP sensor 1 voltage is greater than 4.8 volts.
    • If less than 4.8 volts, test the APP sensor 1 signal circuit for an open or short to ground. If the circuit tests normal, replace the ECM.
  6. Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit terminal C of the APP sensor 2. Verify that the scan tool parameter APP sensor 2 voltage is greater than 4.8 volts.
    • If less than 4.8 volts, test the APP sensor 2 signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
  7. Ignition OFF, disconnect the harness connector at the ECM.
  8. Test for less than 5 ohms on all APP sensor circuits between the following terminals:
    • ECM X1 signal circuit terminal 47 to APP terminal E
    • ECM X1 signal circuit terminal 49 to APP terminal B
    • ECM X1 5-volt reference circuit terminal 35 to APP terminal C
    • ECM X1 5-volt reference circuit terminal 33 to APP terminal F
    • If greater than 5 ohms, repair the affected circuit for an open/high resistance.
  9. Test for infinite resistance between APP sensor 1 signal circuit terminal E and APP sensor 2 signal circuit terminal B.
    • If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuits.
  10. If all circuits test normal, test the APP sensor. Refer to Component Test  for instructions.
    • If the APP sensor tests normal, replace the ECM.
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