Cruise Control System Test No 3 - Ground Circuit Check
- Turn ignition off. Disconnect cruise control servo connector. Connect an ohmmeter between Black wire of cruise control servo connector and ground. If ohmmeter is reading continuity, go to next step. If ohmmeter reads no continuity, repair Black wire for an open circuit to wiring harness splice.
- With tester connected to diagnostic connector, put system in Switch Test Mode. Refer to ENTERING ON-BOARD DIAGNOSTICS in this article. Press down on brake pedal. If display on tester changes as brake pedal was depressed (not important what display changes to, just ensure display changes), go to step 4). If display on tester did not change as brake pedal was depressed, go to next step.
- Turn ignition off. Disconnect 60-pin connector. Connect an ohmmeter between White/Pink wire in cavity No. 29 and ground. Press down on brake pedal and then release. If ohmmeter reads no continuity when brake pedal is pressed down and continuity when brake pedal is released, replace SMEC for a bad logic board. Before replacing SMEC, ensure cavity No. 29 of 60-pin connector is not damaged causing a poor connection. If ohmmeter does not indicate as described, check White/Pink wire of cavity No. 29 for an open circuit through stop light bulb circuit to ground.
- While observing display on tester, put gear selector in Park, Reverse, Neutral, and Drive. If display on tester changes as gear selector is moved, go to step 6). If display on tester did not change when gear selector was moved, go to next step.
- Turn ignition off. Disconnect 60-pin connector from SMEC. Connect an ohmmeter between Brown/Yellow wire in cavity No. 30 and ground. Disconnect battery quick-disconnect. Turn ignition on. Observe ohmmeter while moving gear selector. If ohmmeter reads continuity in all positions, check Brown/Yellow wire of cavity No. 30 of 60-pin connector for a short to ground. Check for a bad neutral safety switch. If ohmmeter reads no continuity in all positions, repair Brown/Yellow wire of cavity No. 30 of 60-pin connector for an open circuit to neutral safety switch. If ohmmeter reads continuity in Park, no continuity in Reverse, continuity in Neutral, and no continuity in Drive (disregard resistance readings, just ensure there is continuity), replace SMEC for a bad logic board. Before replacing SMEC, ensure terminal in cavity No. 30 of 60-pin connector is not damaged causing a poor connection.
- Connect cruise control servo connector. With tester connected, disconnect cruise control servo vacuum supply hose from brake booster and connect a vacuum pump to hose. Put system in ATM Test "08". Refer to ENTERING ON-BOARD DIAGNOSTICS in this article. Continuously apply vacuum to servo. If throttle is opening and closing as vacuum is being applied to cruise control servo, check vacuum supply to servo. Check speed sensor operation using Engine Running Test "71". Refer to ENTERING ON-BOARD DIAGNOSTICS in this article. Display on tester must remain stable. If display is not stable, replace speed sensor.
- If throttle is not opening and closing as vacuum is applied to cruise control servo, replace cruise control servo. Before replacing servo, ensure cruise control cable is properly adjusted and not damaged. Ensure vacuum supply hose is free of leaks and restrictions.