Horn: Overview Ford Explorer IV

Principles of Operation

The battery junction box (BJB) supplies the switched and control voltage to the horn relay (part of the smart junction box [SJB]). When the horn switch (part of the steering wheel) is pressed, ground is supplied to the SJB through the clockspring. The SJB then energizes the horn relay sending voltage to the horn, enabling the horn to sound.

The SJB provides a momentary ground to the horn relay as a configuration confirmation for the auto-locks and for the tire pressure monitoring system (TPMS) sensor training. The SJB also provides a momentary ground to the horn relay when the anti-theft system is armed, and an on then off ground when an intrusion is detected or the panic button is pressed on the remote keyless entry (RKE) key fob.

Normal Operation

The battery junction box (BJB) supplies the switched and control voltage to the horn relay (part of the smart junction box [SJB]) through circuit SBB02 (YE/RD). When the horn switch (part of the steering wheel) is pressed, the switch closes and ground is applied from the steering wheel switch harness through the clockspring to the horn relay through circuit CRH02 (BU/WH). The horn relay is then energized, applying voltage to the horn through circuit CBP14 (VT/OG), enabling the horn to sound. Ground for the horn is supplied through circuit GD120 (BK/GN).

DTC B1217 - sets when the SJB detects a horn relay circuit failure on the horn relay circuit.

Possible Causes

1. Fuse
2. Circuit CBP14 (VT/OG) open
3. Circuit CRH02 (BU/WH) open
4. Circuit GD120 (BK/GN) open
5. Steering wheel switch harness
6. Horn
7. Clockspring
8. Horn switch (part of the steering wheel)
9. SJB

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1. A1 CHECK THE HORN CONTROL COMMAND Connect the diagnostic tool. Key in ON position. Enter the following diagnostic mode on the diagnostic tool: SJB Module Active Commands Select the SJB module. Select the HORN control active command and command the HORN ON. Does the horn sound? YES : Go to A2 . NO : Go to A5 .
2. A2 CHECK CIRCUIT CRH02 (BU/WH) FOR AN OPEN Depower the supplemental restraint system (SRS). Refer to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . Disconnect: SJB C2280c Disconnect: Clockspring C218a Measure the resistance between the clockspring C218a-8, circuit CRH02 (BU/WH), harness side and the SJB C2280c-6, circuit CRH02 (BU/WH), harness side. Is the resistance less than 5 ohms? YES : Go to A3 . NO : REPAIR the circuit. REPOWER the SRS. REFER to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . CLEAR the DTCs. REPEAT the self-test.
3. A3 CHECK THE CLOCKSPRING FOR AN OPEN Remove the driver air bag module. Refer to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . Measure the resistance between the clockspring C218 pin 8, component side and the upper clockspring connector pin 1, component side. Is the resistance less than 5 ohms? YES : Go to A4 . NO : INSTALL a new clockspring. INSTALL the driver air bag module. REFER to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . CLEAR the DTCs. REPEAT the self-test.
4. A4 CHECK THE STEERING WHEEL SWITCH HARNESS FOR DAMAGE OR OPENS Inspect the steering wheel switch harness for damage or opens. Is the steering wheel switch harness OK? YES : INSTALL a new steering wheel. REFER to «STEERING COLUMN»(ref-270916) . CLEAR the DTCs. REPEAT the self-test. NO : REPAIR or INSTALL a new steering wheel switch harness. CLEAR the DTCs. REPEAT the self-test.
5. A5 CHECK CIRCUIT GD120 (BK/GN) FOR AN OPEN Key in OFF position. Disconnect: Horn C1101 Measure the resistance between the horn C1101-1, circuit GD120 (BK/GN), harness side and ground. Is the resistance less than 5 ohms? YES : Go to A6 . NO : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
6. A6 CHECK CIRCUIT CBP14 (VT/OG) FOR AN OPEN Measure the resistance between the SJB C2280e-17, circuit CBP14 (VT/OG), harness side, and the horn C1101-2, circuit CBP14 (VT/OG), harness side. Is the resistance less than 5 ohms? YES : Go to A7 . NO : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
7. A7 CHECK CIRCUIT CBP14 (VT/OG) FOR VOLTAGE Connect: SJB C2280e Measure the voltage between the horn C1101-2, circuit CBP14 (VT/OG), harness side, and the horn C1101-1, circuit GD120 (BK/GN), harness side, while pressing the horn switch. Is the voltage greater than 10 volts? YES : INSTALL a new horn. REFER to «Horn»(ref-270944-S28274974872007110700000) . CLEAR the DTCs. REPEAT the self-test. NO : VERIFY the SJB fuse 14 (20A) is OK. If OK, go to A8 .
8. A8 CHECK FOR CORRECT SJB OPERATION Disconnect all the SJB connectors. Check for: corrosion damaged pins pushed-out pins Connect all the SJB connectors and make sure they seat correctly. Operate the system and verify the concern is still present. Is the concern still present? YES : INSTALL a new SJB. REFER to «MULTIFUNCTION ELECTRONIC MODULES»(ref-270935) . TEST the system for normal operation. NO : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.

Refer to SYSTEM WIRING DIAGRAMS , Horn/Cigar Lighter for schematic and connector information.

The battery junction box (BJB) supplies the switched and control voltage to the horn relay (part of the smart junction box [SJB]) through circuit SBB02 (YE/RD). When the horn switch (part of the steering wheel) is pressed, the switch closes and ground is applied from the steering wheel switch harness through the clockspring to the horn relay through circuit CRH02 (BU/WH). The horn relay is then energized, applying voltage to the horn through circuit CBP14 (VT/OG), enabling the horn to sound.

DTC B1218 - sets when the SJB detects a short to voltage on the horn relay coil circuit.

Possible Causes

1. Circuit CBP14 (VT/OG) short to voltage
2. Circuit CRH02 (BU/WH) short to ground
3. Steering wheel switch harness
4. Clockspring
5. Horn switch (part of the steering wheel)
6. SJB

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1. B1 CHECK CIRCUIT CBP14 (VT/OG) FOR A SHORT TO VOLTAGE Key in OFF position. Disconnect: SJB C2280e Does the horn continue to sound? YES : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test. NO : Go to B2 .
2. B2 CHECK THE HORN SWITCH INPUT Connect: SJB C2280e Disconnect: SJB C2280c Does the horn continue to sound? YES : Go to B6 . NO : Go to B3 .
3. B3 CHECK CIRCUIT CRH02 (BU/WH) FOR A SHORT TO GROUND Depower the supplemental restraint system (SRS). Refer to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . Disconnect: Clockspring C218a Measure the resistance between the clockspring C218a-8, circuit CRH02 (BU/WH), harness side and ground. Is the resistance greater than 10,000 ohms? YES : Go to B4 . NO : REPAIR the circuit. REPOWER the SRS. REFER to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . CLEAR the DTCs. REPEAT the self-test.
4. B4 CHECK THE CLOCKSPRING FOR A SHORT TO GROUND Remove the driver air bag module. Refer to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . Connect: Clockspring C218a Measure the resistance between the SJB C2280c-6, circuit CRH02 (BU/WH), harness side and ground. Is the resistance greater than 10,000 ohms? YES : Go to B5 . NO : INSTALL a new clockspring. INSTALL the driver air bag module. REFER to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . CLEAR the DTCs. REPEAT the self-test.
5. B5 CHECK THE STEERING WHEEL SWITCH HARNESS FOR DAMAGE OR SHORTS Inspect the steering wheel switch harness for damage or shorts. Is the steering wheel switch harness OK? YES : INSTALL a new steering wheel. REFER to «STEERING COLUMN»(ref-270916) . CLEAR the DTCs. REPEAT the self-test. NO : REPAIR or INSTALL a new steering wheel switch harness. INSTALL the driver air bag module. REFER to «SUPPLEMENTAL RESTRAINT SYSTEM»(ref-270926) . CLEAR the DTCs. REPEAT the self-test.
6. B6 CHECK FOR CORRECT SJB OPERATION Disconnect all the SJB connectors. Check for: corrosion damaged pins pushed-out pins Connect all the SJB connectors and make sure they seat correctly. Operate the system and verify the concern is still present. Is the concern still present? YES : INSTALL a new SJB. REFER to «MULTIFUNCTION ELECTRONIC MODULES»(ref-270935) . TEST the system for normal operation. NO : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.

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