Code
P0448
HUMMER
P — Powertrain
Evaporative Emission Control System Vent Control Circuit Shorted
Views:
UK: 16
EN: 29
RU: 28
AI status
Completed
Completed
100%
Causes
- Short to ground in EVAP vent valve wiring
- Short to battery/ignition voltage in EVAP vent valve wiring
- Damaged or corroded vent valve connector
- Failed EVAP vent control valve (internal shorted coil)
- Faulty ECM/PCM driver transistor or pin
- Blown fuse or poor ground related to EVAP circuit
Symptoms
- Check Engine Light (Malfunction Indicator Lamp) illuminated
- Possible EVAP-related MIL strategies (fail to pass readiness)
- Fuel smell near vehicle (if vent stuck open) — less common with pure circuit short
- Failed emissions test or EVAP system not sealing
- Driveability usually unaffected unless additional codes present
What to check
- Retrieve freeze frame and pending codes; note ignition state and conditions when code set
- Visual inspection of EVAP vent valve, connector, and harness for damage, corrosion, or pin deformation
- Check related fuses and ground points for integrity and corrosion
- Backprobe vent valve connector and measure voltage with key ON and while commanded by scan tool
- Measure coil resistance of vent valve with connector disconnected
- Check continuity from vent valve harness to power and ground to identify shorts
Signal parameters
- Battery voltage (approx. 11.5–14.5 V) present on the supply side of the vent valve when ignition ON (depends on circuit design)
- Driver output expected to switch toward ground (0 V) or to battery voltage when commanded — confirm with vehicle-specific service manual
- Typical vent valve coil resistance: approximately 20–40 ohms (check service data for exact value)
- Expected current draw when energized: roughly 0.2–0.8 A (varies by valve)
- Open-circuit (with connector disconnected): no low-resistance path to ground or battery should be present between control and supply/ground
Diagnostic algorithm
- Verify code and note freeze frame, then clear codes and attempt to reproduce. If code returns immediately, proceed.
- Perform a careful visual inspection of the EVAP vent valve, connector, and harness from valve to ECM for abrasion, rodent damage, corrosion, or repairs.
- With ignition ON (engine OFF), backprobe the vent valve connector: measure voltage on the supply pin and the control pin. Compare to expected values from service manual. Do not apply power without fuse protection.
- Disconnect the vent valve connector and measure coil resistance with an ohmmeter. Compare to spec. Very low resistance indicates internal short; infinite or very high indicates open circuit.
- Check for shorts: with connector disconnected, measure continuity from the control wire to battery positive and to ground. A near-zero reading indicates a short to that rail.
- Command the vent valve ON and OFF with a scan tool while monitoring voltage/current. If the ECM should ground the circuit, the control wire will switch toward 0 V when commanded; if it does not, suspect ECM or wiring.
- If wiring checks show a short to power or ground that is not at the valve, isolate sections of the harness and repair/replace damaged wiring or connectors.
- If wiring and valve are good but driver behavior is abnormal (e.g., stuck high or low despite correct wiring), consider replacing the vent valve. If problem persists after valve replacement and wiring repairs, evaluate ECM/PCM driver and replace ECM only after confirming external wiring and components are good.
- After repairs, clear codes and perform drive cycle or readiness checks to verify the code does not return.
Likely causes
- Wiring rubbed through and shorting to chassis ground
- Wire pinched and contacting power feed causing a short to battery
- Connector terminal pushed out, corroded, or water-intruded causing low resistance path
- Vent solenoid coil failed internally, presenting near-short resistance
- PCM output stage damaged from prior short or surge
Fault status
Status
EVAP vent control circuit indicates a short or incorrect voltage condition. Circuit may be shorted to power or ground, vent valve coil may be internally shorted, or ECM driver may be faulty.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
Similar codes
HTML Workshop Manuals AI manual library for HUMMER Click to show available manuals 77
HUMMER 2010 H3 Alpha
HTML ManualHUMMER 2010 H3 Base, Standard
HTML ManualHUMMER 2010 H3 Base, Automatic
HTML ManualHUMMER 2010 H3T Alpha
HTML ManualHUMMER 2010 H3T Base, Standard
HTML ManualHUMMER 2010 H3T Base, Automatic
HTML ManualHUMMER 2009 H2 4D Utility Wagon
HTML ManualHUMMER 2009 H2 4D Utility Pickup
HTML ManualYour experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email