P1646 - FAULT CODE - OBD2

P1646 BUICK, CADILLAC, CHEVROLET, GMC: EVAP VENT SOLENOID OUTPUT CIRCUIT

The EVAP System (Evaporative Emissions Control System) is designed to store the vapors resulting from combustion, preventing them from escaping into the environment and significantly reducing the damage to the environment. This process is achieved through the use of various sensors, valves, and actuators, which are controlled by the Powertrain Control Module (PCM).

The EVAP vent control solenoid is installed in the vessel and its function is basically to seal the flow or air passage of it. The PCM activates the solenoid to energize the coil, which moves a plunger that seals the vent.

The PCM includes chips that are referred to as Output Driver Modules that supply 7 changeable ground outputs employed to operate relays, solenoids, indicators, and various types of devices. Every one of these ground outputs is responsible for feeding back to the PCM’s microprocessor. When the output is Off, the output driver should receive 12 volts fed to the corresponding solenoid, relay, or device. And when the output is On, it should receive 0 volts since it is connecting the output to the ground. If it receives 0 volts when the output is Off or 12 volts when the output is On, it sets the fault line low.

When the P1646 OBDII diagnostic code is set, it is because the EVAP vent solenoid output circuit is detected to have low voltages compared to expected voltages.

• Check Engine light is on.
• Fuel consumption increases

DTC P1646 OBD2 is stored for one of the following reasons:

• EVAP vent solenoid wiring may have been damaged.
• The EVAP vent solenoid output circuit may be faulty.
• The solenoid may be defective.

To troubleshoot the P1646 OBDII fault code you must do the following:

• Consult the Technical Service Bulletins.
• Inspect the condition of the cables and connectors that are related to the EVAP vent solenoid to check for common damage. Repairs conditions created by wear or burnout.
• Performs voltage tests to the vent solenoid output circuit and verifies that the vent solenoid has no poor connections that produce the low voltages. Repair as required.
• If after performing the above tests you still get the P1646 OBDII code, the solenoid is probably defective. Measure the resistance of the solenoid and check that it matches the value specified by the manufacturer, a value outside the allowable range requires replacement of the solenoid.