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Home >> Cadillac >> 2010 >> STS 3.6 V, AWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 18 (Engine Controls And Fuel - 4.6L (LH2) - DTC P0335 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 variant/trim than selected.
NOTE: The first two steps of this diagnostic are necessary for an accurate low reference test result.
  1. Ignition OFF, remove the Driver Dr. Mod. fuse from the left rear fuse block.
  2. All access doors closed and ignition OFF for 90 seconds, access the vehicle from the driver's door while ensuring all other doors remain closed.
  3. Disconnect the harness connector at the accelerator pedal.
  4. Test for less than 5 ohms of resistance 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.
  5. Install the Drivers Dr. Mod. fuse.
  6. 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 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 tests normal, replace the ECM.
  7. 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 appropriate APP sensor 1 or 2 signal circuit terminal B or E for a short to voltage. If the circuit tests normal, replace the ECM.
  8. 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.
  9. 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.
  10. Ignition OFF, disconnect the harness connector at the ECM.
  11. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:
    • The ECM X1 signal circuit terminal 47 to the APP terminal E
    • The ECM X1 signal circuit terminal 49 to the APP terminal B
    • The ECM X1 5-volt reference circuit terminal 35 to the APP terminal C
    • The ECM X1 5-volt reference circuit terminal 33 to the APP terminal F
    • If greater than 5 ohms, repair the affected circuit.
  12. 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.
  13. If all circuits test normal, test or replace the accelerator pedal.
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