Horn Relay: Testing and Inspection

WARNING: ON VEHICLES EQUIPPED WITH AIRBAGS, REFER TO ELECTRICAL, RESTRAINTS BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

Fig. 2 Horn Relay:

The horn relay is located in the Power Distribution Center (PDC) behind the battery on the driver side of the engine compartment. If a problem is encountered with a continuously sounding horn, it can usually be quickly resolved by removing the horn relay from the PDC until further diagnosis is completed. See the fuse and relay layout label affixed to the inside surface of the PDC cover for horn relay identification and location. For complete circuit diagrams, refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pinout information and location views for the various wire harness connectors, splices and grounds.

Relay Continuity Test
1. Remove the horn relay from the PDC.
2. A relay in the de-energized position should have continuity between terminals 87A and 30, and no continuity between terminals 87 and 30.
If OK, go to Step 3.
If not OK, replace the faulty relay.

3. Resistance between terminals 85 and 86 (electromagnet) should be 75 ± 5 ohms.
If OK, go to Step 4.
If not OK, replace the faulty relay.

4. Connect a battery to terminals 85 and 86. There should now be continuity between terminals 30 and 87, and no continuity between terminals 87A and 30.
If OK, perform the Relay Circuit Test that follows.
If not OK, replace the faulty relay.

Relay Circuit Test
1. The relay common feed terminal cavity (30) is connected to battery voltage and should be hot at all times.
If OK, go to Step 2.
If not OK, repair the open circuit to the fuse in the PDC as required.

2. The relay normally closed terminal (87A) is connected to terminal 30 in the de-energized position, but is not used for this application. Go to Step 3.

3. The relay normally open terminal (87) is connected to the common feed terminal (30) in the energized position. This terminal supplies battery voltage to the horn(s). There should be continuity between the cavity for relay terminal 87 and the horn relay output circuit cavity of each horn wire harness connector at all times.
If OK, go to Step 4.
If not OK, repair the open circuit to the horn(s) as required.

4. The coil battery terminal (86) is connected to the electromagnet in the relay It is connected to battery voltage and should be hot at all times. Check for battery voltage at the cavity for relay terminal 86.
If OK, go to Step 5.
If not OK, repair the open circuit to the fuse in the PDC as required.

5. The coil ground terminal (85) is connected to the electromagnet in the relay. It is grounded through the horn switch when the horn switch is depressed. On vehicles equipped with the Vehicle Theft Security System (VTSS), the horn relay coil ground terminal can also be grounded by the Central Timer Module (CTM) in response to certain inputs related to the VTSS or Remote Keyless Entry (RKE) system.
Check for continuity to ground at the cavity for relay terminal 85. There should be continuity with the horn switch depressed, and no continuity with the horn switch released.
If not OK, (Refer to HORN SWITCH - DIAGNOSIS AND TESTING Horn Switch).