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 CARSECTION 56 (POWER SEAT SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESPOWER SEAT INOPERATIVE (W/MEMORY)CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Circuit/System Testing
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Circuit/System Testing
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Seat Adjuster Switch Circuit Test
- Disconnect the MSM connector C7 and verify that none of the adjuster switch inputs are displayed as Active.
- If any of the switch inputs are Active, replace the MSM.
- Verify that battery voltage is not present at the affected switch signal circuit terminal while the switch is inactive.
- If battery voltage is present while the switch is not pressed, replace the seat adjuster switch.
- Verify that battery voltage is present at the affected switch signal circuit terminal while pressing the switch.
- If battery voltage is not present while the switch is pressed, repair the switch supply circuit for an open/high resistance. If the circuit tests normal replace the seat adjuster switch.
- If the circuits test normal replace the MSM.
Lumbar Switch Circuit Test
- Disconnect the MSM connector C6 and verify that none of the lumbar switch inputs are displayed as Active.
- If any of the switch inputs are Active, replace the MSM.
- Verify that battery voltage is not present at the affected switch signal circuit terminal while the switch is inactive.
- If battery voltage is present while the switch is not pressed, replace the lumbar switch.
- Verify that battery voltage is present at the affected switch signal circuit terminal while pressing the switch.
- If battery voltage is not present while the switch is pressed, repair the switch supply circuit for an open/high resistance. If the circuit tests normal replace the lumbar switch.
- If the circuits test normal replace the MSM.
Motor Control Circuit Test
- Disconnect the MSM connector C3.
- Verify that a test lamp illuminates when connected from the high current battery supply circuit terminal 5 to ground.
- If the test lamp does not illuminate, repair the high current battery supply circuit for an open or short to ground.
- Connect the MSM connector C3 and disconnect the seat adjuster assembly or lumbar adjuster assembly connector C2.
- Connect a test lamp across the affected motor control circuit terminals.
- Verify that the test lamp illuminates while the affected switch is pressed.
- If the test lamp does not illuminate, repair the motor control circuits for an open/high resistance. If the circuits test normal replace the MSM.
- If the circuits test normal replace the affected adjuster 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.