Code
P1645
HUMMER
P — Powertrain
Evaporative Emission (EVAP) Vent Solenoid Contorl Circuit
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UK: 27
EN: 32
RU: 26
AI status
Completed
Completed
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Causes
- Open or short in the EVAP vent solenoid wiring harness
- Corroded, loose, or damaged connector at the vent solenoid
- Blown fuse or fault in power/ground supply to the EVAP circuit
- Failed EVAP vent solenoid (coil open or shorted)
- Defective PCM driver or internal PCM fault
- Water intrusion or contamination in connector
Symptoms
- Check Engine Light (MIL) illuminated
- EVAP system diagnostic trouble code stored (P1645)
- Possible fuel smell from fuel tank area
- Failed EVAP readiness or emissions test
- Possible drivability issues or rough idle when purge is commanded (less common)
What to check
- Retrieve freeze frame and live data; confirm P1645 is current and note other EVAP codes
- Visually inspect vent solenoid, connector, and wiring for damage, corrosion, or pin backout
- Check related fuses and vehicle ground(s) for continuity and corrosion
- Back-probe harness at the vent solenoid and check supply voltage with ignition ON
- Measure solenoid coil resistance with connector disconnected
- Command vent solenoid ON/OFF with a scan tool and observe voltage/current response
Signal parameters
- Supply voltage (ignition ON): battery voltage, typically 11–14.5 V at the supply pin
- Coil resistance (typical range): approximately 20–60 ohms (model dependent)
- Operating current when energized: typically 0.2–0.6 A (should not exceed ~1 A)
- When PCM commands ON: driver should switch the control circuit (commonly to ground) — voltage at control pin will change from near battery to near 0 V when commanded (verify with vehicle wiring diagram)
- No voltage or infinite resistance indicates open circuit; near 0 V with short to ground indicates short
Diagnostic algorithm
- Verify code and gather freeze-frame/live data. Note any additional EVAP codes.
- Visually inspect vent solenoid, connector, and wiring harness for damage, corrosion, or water intrusion.
- Check fuses and chassis/body grounds related to the EVAP system.
- Disconnect electrical connector and measure solenoid coil resistance. If out of expected range (open or short), replace solenoid.
- Back-probe the harness supply and control pins with ignition ON. Confirm battery voltage at supply pin and proper control voltage behavior when commanding the solenoid ON/OFF from a scan tool.
- Command the vent solenoid ON with a scan tool and observe voltage/current. If the PCM does not drive the circuit but wiring and fuse are good, suspect PCM driver fault.
- If PCM output appears faulty, perform wiggle tests and continuity checks between PCM and solenoid. Repair any wiring faults (repair or replace damaged wires, terminals, or connector).
- If wiring and PCM driver test OK but operation still fails, verify function by applying fused battery voltage (or ground) carefully to operate the solenoid (use service manual procedure). If it works externally but not from PCM, replace/repair PCM or wiring as appropriate.
- After repair/replacement, clear codes, perform functional test and a drive cycle to confirm the code does not return.
- If intermittent or unresolved, perform more extensive diagnostics (scope PCM driver, consult wiring diagrams, or consult dealer/technical service bulletins).
Likely causes
- Broken/shorted wire between PCM and vent solenoid
- Connector pins corroded or pushed out at solenoid
- Vent solenoid coil open (high resistance) or shorted
- Blown fuse or poor ground connection
- PCM output transistor failed
Fault status
Status
P1645 — EVAP vent solenoid control circuit fault (open/short/driver failure detected).
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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