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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1647 (Engine Control System & Fuel System - 4.8L, 5.3L, 6.0L, 6.2L - DTC P1255 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 car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the harness connector at the accelerator pedal.
  2. Ignition OFF for 1 minute, test for less than 5 Ω between the appropriate low reference circuit terminal listed below and ground.
    • APP sensor 1 terminal F or 4
    • APP sensor 2 terminal A or 5
    • If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.
  3. Ignition ON, test for 4.8-5.2 V between the appropriate 5 V reference circuit terminal listed below and ground.
    • APP sensor 1 terminal D or 2
    • APP sensor 2 terminal C or 1
    • If less than the specified range, test the 5 V reference circuit for a short to ground or open/high resistance. If the circuit/connections test normal, replace the ECM.
    • If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
  4. Observe the scan tool APP sensor 1 voltage parameter. Verify the voltage is less than 0.3 V.
    • If greater than the specified range, test the signal circuit terminal E or 3 for a short to voltage. If the circuit/connections test normal, replace the ECM.
  5. Observe the scan tool APP sensor 2 voltage parameter. Verify the voltage is less than 0.3 V.
    • If greater than the specified range, test the signal circuit terminal B or 6 for a short to voltage. If the circuit/connections test normal, replace the ECM.
  6. Connect a 3 A fused jumper wire between the APP sensor 1 signal circuit terminal E or 3 and the 5 V reference circuit terminal C or 1. Verify the APP sensor 1 voltage parameter is greater than 4.8 V.
    • If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.
  7. Connect a 3 A fused jumper wire between the APP sensor 2 signal circuit terminal B or 6 and the 5 V reference circuit terminal C or 1. Verify the APP sensor 2 voltage parameter is greater than 4.8 V.
    • If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.
  8. If all circuits/connections test normal, test or replace the Accelerator Pedal Assembly.
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