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 DIAGNOSISBRAKESANTI-LOCK BRAKE SYSTEM, TRACTION CONTROL SYSTEM & STABILITY CONTROL SYSTEMDIAGNOSTIC INFORMATION AND PROCEDURESBRAKE PRESSURE MODULATOR VALVE HYDRAULIC TESTINGBRAKE PRESSURE APPLICATION TESTING (W/JL4)TC ISOLATION VALVE TEST PROCEDURE
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
TC Isolation Valve Test Procedure
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION TC Isolation Valve Test Procedure
- Turn OFF the ignition.
- Disconnect the brake switch harness connector.
- Raise the vehicle so that all 4 wheels are about 15 cm (6 in) off of the floor. Refer to Lifting and Jacking the Vehicle .
- Ensure that the park brake is released.
- Turn ON the ignition.
- Ensure that the transmission is in neutral (N).
- Select the VSES Special Functions menu on the scan tool.
- Select either the Left Front Brake Apply or the Right Front Brake Apply, whichever wheel has the most convenient access for you.
- Press the Apply key on the scan tool.
- Listen for the precharge pump to activate for approximately 2 seconds.
- Immediately verify brake activation at the wheel by attempting to turn the wheel by hand.
- Continue attempting to turn the wheel by hand and ensure the wheel remains locked for 9 seconds after the precharge pump turns OFF.
- Verify that the brake releases quickly when the 9 second pressure hold is terminated.
- Select either the Left Rear Brake Apply or the Right Rear Brake Apply, whichever wheel has the most convenient access for you.
- Repeat steps 11, 12, and 13 for the rear wheel being tested.
- Turn OFF the ignition.
- Reconnect the brake switch harness connector.
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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.