"C", "K", "L", "M", "S", & "T"Series

If horns diagnostic system check was performed, go to next step. If horns diagnostic system check was not performed, perform HORNS DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM.
Depress horn switch. If horns operate, go to next step. If horns do not operate, go to step 5.
Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel, to right of steering column. Turn ignition switch to RUN position. Using scan tool, command Body Control Module (BCM) horn output ON and OFF. If horns operate, check for intermittent problem. If horns do not operate, go to next step.
Test BCM portion of horn relay control circuit (Black wire) for high resistance or an open. If problem was found, repair as necessary. After repair, go to step 21. If problem was not found, go to step 11.
Turn ignition switch to OFF position. Remove horn relay. Using test light connected to ground, test battery circuit (Orange wire) of horn relay coil. If test light illuminates, go to next step. If test light does not illuminate, go to step 14.
Connect test light between battery voltage circuit (Orange wire) of horn relay coil and horn relay control circuit (Black wire). Depress and hold horn switch. If test light illuminates, go to next step. If test light does not illuminate, go to step 15.
Using test light connected to ground, test battery voltage circuit of horn relay switch (Orange wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 16.
Momentarily connect a 15-amp fused jumper between battery positive voltage circuit (Orange wire) of horn relay switch and horn control circuit (Dark Green wire). If horns do not operate, go to next step. If horns operate, go to step 12.
Install horn relay. Disconnect either horn harness connector. Connect test light between horn control circuit and ground. Depress and hold horn switch. If test light illuminates, go to next step. If test light does not illuminate, go to step 17.
Connect test light between horn control circuit (Dark Green wire) and horn ground circuit (Black wire). Depress and hold horn switch. If test light illuminates, go to step 13. If test light does not illuminate, go to step 18.
Inspect for poor connections at harness connector of BCM. If problem was found, repair as necessary. After repair, go to step 21. If problem was not found, go to step 19.
Inspect for poor connections at horn relay. If problem was found, repair as necessary. After repair, go to step 21. If problem was not found, go to step 20.
Repair high resistance in horn control circuit or horn ground circuit. A resistance as low as.5 ohms could cause operating problems with the horns. It is possible that both horns are defective. After repair, go to step 21.
Repair open or high resistance in battery voltage circuit of horn relay coil (Orange wire). After repair, go to step 21.

NOTE: Horn relay control circuit includes horn slip ring and horn switch.

Repair open or short to voltage in horn relay control circuit (Black wire). After repair, go to step 21.
Repair open or high resistance in battery voltage circuit of horn relay switch (Orange wire). After repair, go to step 21.
Repair open or high resistance in horn control circuit (Dark Green wire). After repair, go to step 21.
Repair open or high resistance in horn ground circuit (Black wire). After repair, go to step 21.
Replace BCM. See appropriate BODY CONTROL MODULES article. After repair, go to step 21.
Replace horn relay. After repair, go to next step.
Operate horn to verify repair. If horns do not operate correctly, repeat test beginning at step 2.