DTC 31

Code 31 "Canister Purge Solenoid Circuit":

Wiring Diagram - Canister Purge Solenoid Circuit:

CODE 31

CANISTER PURGE SOLENOID CIRCUIT


Circuit Description:
Canister purge is controlled by a normally closed solenoid that allows manifold vacuum to purge the canister when energized. The ECM supplies a ground to energize the solenoid (purge "ON"). The ECM monitors the voltage on terminal "17". Code 31 indicates the canister purge control, terminal "17", voltage is incorrect as follows:

Terminal "17" voltage low when purge commanded "ON."

Terminal "17" voltage high when purge commanded "OFF."

Above conditions exist for a calibrated time.

If the diagnostic test terminal is grounded with the engine stopped, the purge solenoid is energized (purge "ON").


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. The canister purge solenoid should not be energized with ignition "ON," engine not running; therefore, the test light should be "OFF." If the light is "ON," either CKT 428 is shorted to ground or the ECM is providing the ground, indicating a faulty ECM.

2. This step checks for battery voltage at canister purge solenoid connector.

3. Grounding the diagnostic test terminal should energize the solenoid circuit, turning "ON" the test light if the ECM and wiring are OK.

4. A low resistance solenoid would allow too much current into the ECM when terminal "17" is switched to ground, causing terminal "17" voltage to be high even when the ECM is commanding it to be low.


5. The previous steps have verified that the wiring and solenoid are OK. Faulty connections at the solenoid could cause an open circuit, resulting in Code 31. If connections are OK, the problem is not present.

Diagnostic Aids:

The CCP driver is a QDR which is "protected." This means it will turn "OFF" or increase its internal resistance to limit current if too much current starts to flow into terminal "17". This would result from a shorted canister purge solenoid or a short to voltage on CKT 428, and would cause terminal "17" voltage to be high even with purge commanded "ON." Low voltage at terminal "17" with OFF" would result from an open from battery positive.