Code
P0449
HUMMER
P — Powertrain
Evaporative Emission (EVAP) Vent Solenoid Control Circuit
Views:
UK: 17
EN: 39
RU: 30
AI status
Completed
Completed
100%
Causes
- Open or short in vent solenoid harness
- Corroded/damaged vent solenoid connector
- Failed EVAP vent solenoid (coil or internal valve)
- Blown fuse or faulty relay feeding the EVAP circuit
- Poor PCM/ECM ground or power supply
- PCM/ECM internal fault (less common)
Symptoms
- MIL (Check Engine) illuminated
- Failed EVAP or emissions test
- Possible fuel odor near filler or charcoal canister
- Usually no noticeable driveability problems
- Occasional EVAP-related diagnostic trouble codes present
What to check
- Retrieve all EVAP-related codes and freeze frame data with a scan tool
- Visually inspect wiring and connectors at the EVAP vent solenoid and PCM
- Check fuses and relays related to EVAP/PCM power
- Back-probe connector to verify supply voltage and ground when commanded
- Measure vent solenoid coil resistance with an ohmmeter
- Perform wiggle test on harness while monitoring data for intermittent faults
Signal parameters
- Coil resistance: typically in the low tens of ohms (example 10–50 Ω) — consult vehicle service manual for exact spec
- Supply voltage: battery voltage (~12 V) present at supply pin with key on
- Control signal: PCM typically supplies ground-side switching; expect near 0 V when commanded to ground, open/high when not commanded
- Applied voltage test: direct 12 V to solenoid should activate valve (listen for click) — use fused jumper
- Scan-tool data: PCM will show vent solenoid commanded ON/OFF states and may show status feedback (refer to factory data)
Diagnostic algorithm
- Use a scan tool to confirm P0449 and check for any related EVAP codes; record freeze frame data and readiness status.
- Visually inspect the vent solenoid, harness, and connector for damage, contamination, or corrosion. Repair any obvious issues.
- With ignition ON, back-probe the solenoid connector: verify battery voltage on the power/feed pin and a switched ground or control signal on the control pin when the PCM commands the vent. If no power, check fuses/relays and feeds.
- With engine off, measure coil resistance across the solenoid terminals. Compare to service manual; if open or shorted out-of-spec, replace the solenoid.
- Command the vent solenoid ON/OFF with a scan tool while observing voltage/ground and listening for the solenoid click. If the solenoid clicks with direct 12 V but not when commanded, suspect wiring/PCM control.
- If harness and solenoid test good, perform a continuity check from the PCM control pin to the solenoid connector to find opens/shorts to ground or battery. Repair wiring as required.
- If wiring and solenoid verify good and the PCM does not provide the expected control, check PCM power/grounds and perform a PCM pin circuit test. Consider PCM replacement only after all other causes are eliminated.
- Clear codes and perform a drive cycle or EVAP self-test to confirm repair.
Likely causes
- Broken or chafed wiring between PCM and vent solenoid
- Corrosion or bent pins at vent solenoid connector
- Vent solenoid stuck or electrically failed
- Aftermarket equipment or recent repairs disturbed wiring
- Intermittent connector making contact when hot/cold
Fault status
Status
EVAP vent solenoid control circuit malfunction detected — PCM did not observe expected electrical response when commanding vent solenoid.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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