Powertrain Controls - ECM/PCM

DTC 26.:

Evaporative Purge Solenoid Valve Circuit.:

CIRCUIT DESCRIPTION
Ignition voltage is supplied directly to the EVAP canister purge solenoid valve on CKT 439. The Powertrain Control Module (PCM) controls the solenoid valve by providing the ground path through CKT 428.

When the PCM is commanding a component "ON," the voltage of the control circuit should be "low" (near 0 volts). When the PCM is commanding the control circuit to a component "OFF," the voltage potential of the circuit should be "high" (near battery voltage). The primary function of the driver is to supply the ground for the component being controlled.

Each driver has a fault line which is monitored by the PCM. The PCM will monitor the voltage at the driver. If the fault detection circuit senses a voltage other than what is expected, the fault line status will change and the DTC will set.

DTC 26 WILL SET WHEN:
The PCM detects the wrong voltage potential for 26 seconds on CKT 428.

ACTION TAKEN (PCM will default to):
The Malfunction Indicator Lamp (MIL) will illuminate and the PCM disables the driver for this circuit to prevent internal PCM damage.

DTC 26 WILL CLEAR WHEN:
The fault condition(s) no longer exist, and the ignition switch cycled "OFF" then "ON."

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test determines if the device can be controlled by the PCM.
2. This check can detect a partially shorted coil which would cause excessive current flow. If excessive current flow is detected, a circuit check will be performed to isolate the device from the wiring. Leave the circuit energized for 2 minutes to allow the coil to warm up. The coil may open (amps drop to "0") when warm.
3. The remaining circuit checks will identify a circuit problem that has caused an excessive current flow or inoperative solenoid.

DIAGNOSTIC AIDS
Inspect the harness and all related connectors including connections at the PCM. These may cause an intermittent. Check for damaged or pushed out terminals.