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Home >> Chevrolet >> 2006 >> Cobalt LTZ >> Repair and Diagnosis >> External Pages >> Different car >> Section 783 (Engine Control System & Fuel System - 2.2L (L61) - DTC P0412 To DTC P2544) >> DTC P2120, P2122, P2123, P2125, P2127, P2128, or P2138 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 Pontiac G5 and 2008 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition ON, disconnect the accelerator pedal harness connector at the accelerator pedal. Allow sufficient time for the ECM to power down.
  2. Test for less than 3 ohms between each low reference circuit terminals A and D and ground.
    • If greater than 3 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  3. Ignition ON, test for 4.8-5.2 volts between each 5-volt reference circuit terminals C and F and ground.
    • If less than 4.8 volts, test 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 affected 5-volt reference circuit for a short to voltage. If the circuit tests 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, and verify the 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, and verify that the 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:
    • The signal circuit terminal B to the corresponding ECM terminal.
    • The signal circuit terminal E to the corresponding ECM terminal.
    • The 5-volt reference circuit terminal C to the corresponding ECM terminal.
    • The 5-volt reference circuit terminal F to the corresponding ECM terminal.
    • If greater than 5 ohms, repair the affected circuit.
  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 circuit.
  10. If all circuits test normal, replace the accelerator pedal.
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