Circuit Description

Ignition voltage is supplied directly to EVAP vent valve relay coil. PCM controls solenoid by grounding control circuit through an internal switch called a driver. Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by PCM.

When PCM is commanding a component on, voltage of control circuit should be low (near zero volts). When PCM is commanding control circuit to a component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, fault line status will change, causing DTC to set.

DTC will set when engine speed is greater than 80 RPM, ignition voltage 9-18 volts, PCM detects commanded state of driver and actual state does not match or a short to ground, open circuit, or a short to battery voltage is detected on control circuit and these conditions are met for 30 seconds.