Horns Malfunction
Diagnostic Instructions
Diagnostic Fault Information
Circuit
|
Short to Ground
|
Open/High Resistance
|
Short to Voltage
|
Signal Performance
|
Horn Switch Signal
|
1
|
2
|
2
|
-
|
Horn Relay Control
|
B2750 02
|
B2750 04
|
B2750 01
|
-
|
Horn Assembly Control
|
2
|
2
|
1
|
-
|
Horn Assembly Ground
|
-
|
2
|
2
|
-
|
Horn Switch Ground
|
-
|
2
|
2
|
-
|
1. Horn Always On
2. Horn Inoperative
|
|
| |
Circuit/System Description
The body control module (BCM) monitors the horn switch signal
circuit, when the horn pad is pressed, the BCM detects the drop in
the horn switch signal circuit and provides a ground for the Horn
PCB relay within the underhood fuse block. The underhood fuse block
will then provide B+ voltage to the horn control circuit, sounding
the horns
Diagnostic Aids
A short to ground in the horn relay control circuit or a short
to voltage in the horn control circuit will cause the horns to
sound continuously until the horns overheat and become
inoperative.
Rotate the steering wheel while pressing the horn pad to
identify intermittent and poor connections within the steering
column.
If diagnosing a Horn- Poor Tone condition, inspect the
following:
| • |
Debris or water in the horn
assembly |
| • |
Debris in the joint where the
horns attach to the vehicle |
| • |
Debris in direct contact with
the horn |
| • |
Vehicle components vibrating
while the horn is sounding |
Reference Information
Schematic Reference
Horn Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Horns System Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
| 1. |
Command the Horn Relay ON and
OFF with the scan tool, the P12 horns should turn ON and OFF when
changing between the commanded states. |
| ⇒ |
If the P12 horns are always ON or always OFF,
refer to Horns or Horn Command Malfunction. |
| ⇒ |
If the sound emitted from the P12 horns are not
clear and even, refer to Horn - Poor Tone. |
| 2. |
Command the P12 horns ON and
OFF by pressing and releasing the horn pad. The P12 horns should
turn ON and OFF when changing between the commanded states.
|
| ⇒ |
If horns are always OFF, refer to Horn Switch
Malfunction. |
Circuit/System Testing
Horns or Horn Command Malfunction
| 1. |
Ignition OFF, disconnect the
X2 harness connector at the X50A underhood fuse block. |
| 2. |
Connect a test lamp between
the control circuit terminal 25 and B+. |
| 3. |
Ignition ON, command the Horn
Relay ON and OFF with a scan tool. The test lamp should turn ON and
OFF when changing between the commanded states. |
| ⇒ |
If the test lamp is always ON, test the control
circuit for a short to ground. If the circuit tests normal, replace
the K9 BCM. |
| ⇒ |
If the test lamp is always OFF, test the control
circuit for a short to voltage or an open/high resistance. If the
circuit tests normal, replace the K9 BCM. |
| 4. |
Ignition OFF, connect the X2
harness connector at the X50A underhood fuse block. Disconnect the
harness connector at the P12 horn assembly. |
| 5. |
Test for less than 1 Ω
between the ground circuit terminal 1 and ground. |
| ⇒ |
If greater than the specified range, test the
ground circuit for an open/high resistance. |
| 6. |
Connect a test lamp between
the control circuit terminal 2 and ground. |
| 7. |
Ignition ON, command the Horn
Relay ON and OFF with a scan tool. The test lamp should turn ON and
OFF when changing between the commanded states. |
| ⇒ |
If the test lamp is always ON, test the control
circuit for a short to voltage. If the circuit tests normal,
replace the X50A underhood fuse block. |
| ⇒ |
If the test lamp is always OFF, test the control
circuit for a short to ground or an open/high resistance. If the
circuit tests normal, test or replace the X50A underhood fuse
block. |
| 8. |
If all circuits test normal,
test or replace the P12 horn assembly. |
Horn - Poor Tone
| 1. |
Ignition OFF, disconnect the
harness connector at the P12 horn assembly. |
| 2. |
Test for less than 1 Ω
between the ground circuit terminal 1 and ground. |
| ⇒ |
If greater than the specified range, test the
ground circuit for high resistance. |
| 3. |
Disconnect the X1 harness
connector at the X50A underhood fuse block. |
| 4. |
Test for less than 1 Ω
between the control circuit terminal 17 at the X50A underhood fuse
block and the control circuit terminal 2 at the P12 horn
assembly. |
| ⇒ |
If greater than the specified range, test the
control circuit for high resistance. |
| 5. |
If all circuits test normal,
test or replace the P12 horn assembly. |
Horn Switch Malfunction
| 1. |
Ignition OFF, disconnect the
harness connector at the S33 horn switch. |
| 2. |
Test for less than 30 Ω
between the ground circuit terminal A and ground. |
| ⇒ |
If greater than the specified range, test the
ground circuit for an open/high resistance. |
| 3. |
Ignition ON, test for greater
than 10V between the signal circuit terminal B and ground.
|
| ⇒ |
If less than the specified value, test the signal
circuit for a short to ground or an open/high resistance. If the
circuit tests normal, replace the K9 BCM. |
| 4. |
If all circuits test normal,
test or replace the S33 horn switch. |
Component Testing
Horn Test
| 1. |
Ignition OFF, disconnect the
harness connector at the P12 horn assembly. |
| 2. |
Install a 15 A fused jumper
wire between the control terminal 2 and 12 V. Install a jumper wire
between the ground terminal 1 and ground. Verify the P12 horns
emits a clear and even tone. |
| ⇒ |
If the sound emitted is not clear and even,
replace the P12 horn assembly. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
|
