How to Fix Diagnostic Code P1645

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🚨 Diagnostic Profile

Vehicle Make: Chevrolet (CHEVY)

Fault Description: EVAP Solenoid Output Circuit

Short description: The Evaporative Emission (EVAP) control system uses solenoid-operated valves, such as the purge and vent solenoids, to manage fuel vapor flow. This profile covers a fault in the driver output circuit that commands these solenoids. Confirm the exact DTC and vehicle year, engine, and model before proceeding, as GM platforms vary in solenoid placement and circuit design between truck, car, and crossover architectures.

🚨 Repair Difficulty Tier

Tier: [Intermediate]

Basis: Diagnosis requires a digital multimeter, a scan tool capable of bidirectional EVAP control, and a basic understanding of circuit testing. Component replacement is often straightforward, but wiring faults can require careful access and inspection, particularly if the vent solenoid is integrated into a canister assembly mounted near the fuel tank.

🛠️ Resolution Steps

Step 1: Preliminary Inspection

  • Verify the DTC and freeze frame data with a scan tool and record all related codes, including any companion EVAP monitor codes (small/large leak, purge flow, or vent solenoid performance codes).
  • Inspect the fuel cap, filler neck, and EVAP hoses for cracks, disconnections, or rodent damage.
  • Locate the EVAP solenoid assemblies: on most Chevrolet platforms, the purge solenoid is mounted on or near the intake manifold/throttle body area under the hood, while the vent solenoid is typically mounted at or near the EVAP canister close to the fuel tank, often accessible from under the vehicle.
  • Inspect the solenoid electrical connectors for corrosion, bent pins, pushed-back terminals, or moisture intrusion.
  • Check the related fuses and relays at the underhood fuse/relay center (consult the fuse box lid label or owner’s manual for the specific PCM ignition feed and EVAP solenoid fuse designation) for proper operation.
  • Inspect the harness routing near the canister, fuel tank straps, and body structure for chafing, heat damage, or pinched sections, as these solenoids are frequently exposed to road debris and corrosion.

Step 2: Diagnostic Verification

  • Measure the supply voltage at the solenoid connector with the key on, engine off: expect to see battery/ignition reference voltage (typically close to 12V) on the power feed circuit using a digital multimeter referenced to a known good chassis ground.
  • With the scan tool commanding the solenoid on and off (bidirectional control), monitor the control circuit for a change in voltage state or duty cycle pulsing as the PCM grounds or releases the circuit; a circuit that never changes state when commanded indicates an open or shorted control wire, a failed driver in the PCM, or a stuck solenoid.
  • Measure coil resistance at the solenoid with the connector disconnected and key off; compare the reading against the OEM specification listed in the service information for the exact year/engine, since purge and vent solenoid coil resistance values differ by design and supplier.
  • Check circuit continuity and resistance to ground and to voltage on the output circuit against the service information for this model, confirming there are no shorts to power, shorts to ground, or open circuits between the PCM connector and the solenoid connector.
  • Use the scan tool to command the solenoid and confirm an audible click at the solenoid body or a corresponding change in the live data PID (such as EVAP Purge Duty Cycle % or Vent Solenoid Commanded State).
  • Confirm whether the fault is in the component, the wiring, or the control module before replacing parts by swapping a known-good solenoid if available, or by back-probing the PCM connector to verify the driver output switches correctly.

Step 3: Resolution & Reset Process

  • Repair any damaged wiring or connectors using the approved soldered splice and adhesive-lined heat shrink or OEM-approved connector repair procedure, and verify the repair with continuity and resistance testing before reassembly.
  • Replace the faulty solenoid or related component only after confirming the failure with testing; always clean the mounting area and replace any mounting grommets or seals to prevent vacuum leaks.
  • Reconnect all hoses and electrical connectors, ensuring they are fully seated and secured, and route harnesses away from heat sources and moving suspension components.
  • Clear the DTCs with the scan tool and perform an EVAP monitor readiness check to confirm the monitor resets to “not ready” status.
  • Complete a GM-specific EVAP monitor drive cycle as specified in the service information: this generally involves a cold soak of several hours, a cold start with fuel level between 1/4 and 3/4 tank, idle time, then a combination of steady-state highway speed and stop-and-go city driving to allow the PCM to run the purge and vent solenoid tests and complete the Non-Integrating/Integrating EVAP monitor.
  • Recheck for pending or stored codes after the drive cycle to confirm the repair and verify the EVAP monitor has run and passed.

📦 Parts, Labor, and Budget Estimates

Required Components/Software:

  • EVAP purge solenoid or vent solenoid assembly (OEM or OE-equivalent recommended for emissions system integrity)
  • Connector pigtail, terminals, dielectric grease, and heat-shrink butt connectors or a harness repair kit (if wiring damage is found)
  • Replacement EVAP hoses, grommets, and clamps (if cracked or deteriorated)
  • Scan tool with bidirectional EVAP control capability (factory-level GM tool such as a Tech2/MDI2 with GDS2, or a quality aftermarket scan tool with bidirectional GM EVAP support) and access to GM service information (such as ACDelco TDS or a comparable subscription)

Average Component Price:

  • Purge solenoid assembly: approximately $40–$120 (part only)
  • Vent solenoid or canister vent valve assembly: approximately $60–$180 (part only, higher if integrated with the canister)
  • Harness or connector repair materials: approximately $15–$60
  • Hoses and clamps: approximately $10–$40
  • Total parts estimate: approximately $75–$300 depending on which component(s) require replacement

Estimated Labor Hours:

  • Diagnosis and verification: approximately 0.5–1.2 hours
  • Purge solenoid replacement: approximately 0.3–0.6 hours; vent solenoid/canister replacement: approximately 0.5–1.5 hours (longer if fuel tank or skid plate removal is required for access on certain truck/SUV platforms)
  • Wiring repair (if required): approximately 0.5–1.5 hours depending on harness accessibility
  • Post-repair verification and drive cycle: approximately 0.3–0.5 hours shop time, though the full drive cycle itself may take 20–40 minutes of actual driving

Total estimated out-of-pocket cost (parts and labor combined, at an average shop labor rate of $100–$160/hr) typically ranges from approximately $150 for a straightforward purge solenoid swap to $450–$600 for a vent solenoid/canister replacement combined with wiring repair.