"Service Engine Soon" Light Is On

NOTE: Illumination of "SERVICE ENGINE SOON" light indicates a malfunction of control module, solenoid or wiring. Check solenoid and module connectors for proper connection.

Disconnect air temperature switch. Install a jumper wire across switch terminals. With ignition on, disconnect each solenoid connector. Using a test light, check for a light from the Pink/Black wire to ground. If light does not illuminate, check for open at circuit No. 39 to solenoid.
If light illuminates, check for a light across terminals. Circuit is okay if there is a light. Check solenoid coil resistance. If coil resistance is less than 20 ohms, replace solenoid and valve.
If there is no light, check for open in circuit No. 900 to air temperature switch, open in circuit No. 436 or faulty control module.
Connect solenoid connectors. Disconnect both connectors at control module. Check for a light between terminals "A" and "B" of 5-pin connector. If test light does not illuminate, check for open circuit to module.
If test light illuminates, check for a light between 5-pin connector harness terminals "A" and "D". If test light illuminates, check for short to ground in circuit No. 419. If test light does not illuminate, check for open in circuit 900 between solenoid terminal "B" and module 2-pin connector terminal "A". If circuit No. 900 is not open, replace control module. See Figure , Figure and Figure .