Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 14 (ENGINE CONTROL SYSTEM & FUEL SYSTEM - 6.6L (LMM) - DTC P0700 TO DTC P2463)DTC P2122, P2123, P2127, P2128, OR P2138CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
WARNING: This page is about a different variant/trim than selected.
- Ignition OFF for 90 seconds, disconnect the harness connector at the APP sensor.
- Ignition OFF, test for less than 5 ohms between each low reference circuit terminals 5 and 4, and ground.
- If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
- Ignition ON, test for 4.8-5.2 volts between each APP sensor 5-volt reference circuit terminals 1 and 2, and ground.
- If less than the specified range, test the affected 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
- If greater than the specified range, test the affected 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- Verify that the scan tool APP Sensor 1 and APP Sensor 2 parameters are less than 0.02 volt.
- If greater than 0.02 volt, test the applicable signal circuit terminals 3 or 6 for a short to voltage. If the circuit tests normal, replace the ECM.
- Install a 3A fused jumper wire between each signal circuit terminals 3 or 6 and the 5-volt reference circuit. Verify that the scan tool APP Sensor parameter is greater than 4.57 volts.
- If less than the specified range, test the applicable signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
- Ignition OFF, disconnect the harness connector at the ECM.
- Test for less than 5 ohms on all APP sensor circuits between the following terminals:
- The ECM X2 signal circuit terminal 49 to APP terminal 3
- The ECM X1 signal circuit terminal 21 to APP terminal 6
- The ECM X1 5-volt reference circuit terminal 38 to APP terminal 1
- The ECM X2 5-volt reference circuit terminal 15 to APP terminal 2
- If greater than the specified range, repair the affected circuit for open/high resistance.
- Test for infinite resistance between APP sensor 1 and 2 signal circuits.
- If less than infinite resistance, repair the short between signal circuits.
- If all circuits test normal, test or replace the accelerator pedal assembly.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.