Code
C0663
HUMMER
C — Chassis
Level Control Exhaust Valve Circuit High
AI status
Completed
Completed
100%
Causes
- Short to battery/constant 12V on the exhaust valve control circuit
- Failed/external coil shorted solenoid (exhaust valve)
- Corroded, damaged or loose connector(s) at the valve or module
- Open or poor ground for the control module or valve power/ground
- Blown/incorrect fuse or relay supplying the valve circuit
- Faulty body/level control module or software/firmware error
Symptoms
- Level control warning lamp or message on instrument panel
- Vehicle does not level automatically or incorrect ride height
- Suspension may remain high or low on one or more corners
- Compressor may run continuously or not run at all
- Related ride/handling complaints (harsh or uneven ride)
What to check
- Scan for stored/active codes and record freeze frame/live data
- Visually inspect wiring and connectors for damage, corrosion or pinching from the valve to the level control module
- Check fuses and relays for the air suspension/level control circuits
- Backprobe the valve connector and measure voltage with key ON and while commanding the valve with a scan tool
- Measure solenoid coil resistance at the valve connector (compare to service spec)
- Check for proper ground(s) at module and valve locations
Signal parameters
- Resting (inactive) control circuit voltage: near 0–1 V (if module grounds the circuit) — verify with service manual
- Commanded (active) voltage: should switch to supply or ground depending on design; expected ~battery voltage (~12 V) or near 0 V when driven — consult vehicle specs
- Solenoid coil resistance: check service manual; commonly in the low ohm range (tens of ohms), measure with valve disconnected
- Current draw when activated: should be within spec (excessive current suggests shorted coil)
- Observe duty cycle or on/off state via scan tool if circuit is PWM-driven
Diagnostic algorithm
- Record all codes and freeze-frame data. Note related codes that may indicate module/communications faults.
- Visually inspect harness, connectors, and grounding points for damage, corrosion, pushed-out pins, or water intrusion.
- Verify fuses/relays for the level/air suspension circuit. Replace any faulty items and re-check.
- With connector disconnected, measure resistance of the exhaust valve solenoid. Compare to service spec; a near short (very low resistance) indicates a failed coil.
- Backprobe the valve harness at the connector. With key ON (engine OFF) and with scanner commanding the valve, measure voltage. A steady high voltage when the circuit should be low indicates a short to battery or stuck supply.
- Check for continuity to battery (short) from the control pin when it should be inactive. Isolate sections of harness to locate short (disconnect connectors progressively).
- Check module pin voltages and grounds. If harness and solenoid check OK, inspect module output driver for damage. Swap or bench-test valve with known-good unit if available.
- Repair or replace damaged wiring, connectors, fuse/relay, or the exhaust valve as indicated by tests.
- If wiring and valve are good, suspect control module. Confirm communications and related modules; reprogram or replace module only after verifying external circuit integrity.
- Clear codes and perform function tests and a road/park verification to ensure the fault does not return.
Likely causes
- Shorted wiring to battery (most common when code reads ‘High’)
- Failed exhaust valve solenoid (internal short or internal failure)
- Corroded/loose connector at the valve or module
- Faulty control module output (less common)
Fault status
Status
Level Control Exhaust Valve Circuit High — the level control module detected an abnormally high voltage condition on the exhaust valve control circuit. This can prevent proper valve operation and impair automatic leveling.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Repair manuals
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138
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