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DTC codes / GM codes / P1645

P1645 · GMBoost Control Solenoid Circuit / EVAP Solenoid Output

P1645 on a GM vehicle indicates that the powertrain control module has detected an abnormal condition on the boost control solenoid circuit or the evaporative emission control solenoid output circuit. The computer monitors the expected voltage or current on the control wire and sets the code when the signal falls outside the programmed range, often due to an open, short, or faulty solenoid.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Reduced engine performance or lack of boost on turbocharged models
  • Rough idle or stumble if the EVAP solenoid is affected
  • A noticeable fuel odor or difficulty fueling if the EVAP system is involved
  • Intermittent warning light that may clear and reset under certain driving conditions

Common causes, most likely first

  1. Failed boost control solenoid or EVAP purge solenoid
  2. Damaged, corroded, or disconnected wiring or connector at the solenoid
  3. Open or shorted circuit in the control wire between the PCM and solenoid
  4. Poor ground connection for the solenoid circuit
  5. Faulty powertrain control module driver (rare but possible)
  6. Vacuum hose leaks or blockages affecting solenoid operation

How to diagnose and fix it

  1. Connect a scan tool and verify P1645 is current; record freeze-frame data to see when it set
  2. Inspect the boost control solenoid and EVAP solenoid connectors for corrosion, loose pins, or damage
  3. Check the solenoid resistance with a multimeter and compare to factory specifications
  4. Test the control circuit for continuity, shorts to ground, and shorts to voltage between the PCM and solenoid
  5. Apply 12 volts directly to the solenoid to confirm it clicks and functions mechanically
  6. Inspect vacuum hoses and lines for cracks, leaks, or disconnections
  7. If all electrical and mechanical checks pass, suspect the PCM and perform further diagnostics before replacement

Don't overlook the simple wiring faults

  • A chafed wire near the exhaust manifold or a corroded ground can mimic a failed solenoid, so always inspect the harness before replacing parts.
  • On some GM trucks, the boost control solenoid and EVAP solenoid share a common power feed, so a blown fuse or relay can set this code for both circuits.
  • The code can be set by a mechanical vacuum leak that prevents the solenoid from achieving the expected pressure change, even when the electrical circuit is perfect.
  • Intermittent P1645 often traces to a loose connector that tests fine when stationary but loses contact under engine vibration.
  • Replacing the solenoid without clearing the adaptive learning values may cause the code to return until the PCM relearns the circuit.

Can I keep driving with P1645?

You can usually drive the vehicle with P1645 set, but avoid heavy acceleration or towing if boost control is affected, as the engine may enter a reduced-power mode. Have the fault diagnosed soon to prevent potential damage to the turbocharger or EVAP system.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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