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 G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 947 (POWER SEAT SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC B3920 OR B3921CIRCUIT/SYSTEM TESTING
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6
Circuit/System Testing
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Circuit/System Testing
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- Ignition OFF, disconnect the C1 harness connector at the MSM.
- Ignition ON, verify that a test does not illuminate between any of the following motor control circuits and ground:
- Front vertical motor terminal 12
- Front vertical motor terminal 13
- Rear vertical motor terminal 15
- Rear vertical motor terminal 16
- Seat horizontal motor terminal 9
- Seat horizontal motor terminal 10
- If the test lamp illuminates, test the control circuit for a short to voltage.
- Test for infinite resistance between the following motor control circuits and ground:
- Front vertical motor terminal 12
- Front vertical motor terminal 13
- Rear vertical motor terminal 15
- Rear vertical motor terminal 16
- Seat horizontal motor terminal 9
- Seat horizontal motor terminal 10
- If less than infinite resistance, test the motor control circuit for a short to ground.
- Test for greater resistance values than specified between the following motor control circuits:
- 1 ohm for front vertical motor terminal 12 and terminal 13
- 1 ohm for rear vertical motor terminal 15 and terminal 16
- 10 ohms for seat horizontal motor terminal 9 and terminal 10
- If less than the specified resistance, test the control circuits for a short together or shorted motor.
- Ignition OFF, disconnect the C4 harness connector at the MSM.
- Ignition ON, verify that a test does not illuminate between any of the following motor control circuits and ground:
- Lumbar vertical motor terminal 1
- Lumbar vertical motor terminal 2
- Lumbar horizontal motor terminal 12
- Lumbar horizontal motor terminal 13
- Seat recline motor terminal 15
- Seat recline motor terminal 16
- Adjustable pedal motor terminal 9
- Adjustable pedal motor terminal 10
- If the test lamp illuminates, test the control circuit for a short to voltage.
- Test for infinite resistance between the following motor control circuits and ground:
- Lumbar vertical motor terminal 1
- Lumbar vertical motor terminal 2
- Lumbar horizontal motor terminal 12
- Lumbar horizontal motor terminal 13
- Seat recline motor terminal 15
- Seat recline motor terminal 16
- Adjustable pedal motor terminal 9
- Adjustable pedal motor terminal 10
- If less than infinite resistance, test the motor control circuit for a short to ground.
- Test for greater resistance values than specified between the following motor control circuits:
- 10 ohms for lumbar horizontal motor terminal 12 and terminal 13
- 1 ohm for recline motor terminal 15 and terminal 16
- If less than the specified resistance, test the control circuits for a short together or shorted motor.
- If all circuits test normal, replace the MSM.
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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.