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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1863 (Engine Controls And Fuel - 2.4L (Lat) - DTC P0420 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 2007 Saturn Vue. 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 of resistance 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 control module.
    • If greater than 5.2 volts, test affected 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.
  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 3-amp 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 control module.
  6. Install a 3-amp 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 control module.
  7. Ignition OFF, disconnect the harness connector at the ECM.
  8. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:
    • ECM C1 signal circuit terminal 47 to APP terminal E
    • ECM C1 signal circuit terminal 49 to APP terminal B
    • ECM C1 5-volt reference circuit terminal 35 to APP terminal C
    • ECM C1 5-volt reference circuit terminal 33 to APP terminal F
    • 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.
    • If all circuits test normal, replace the accelerator pedal.
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