Checking the Horn
Checking the horn
Checking the input signal
Press the horn. Check that the signal from the horn reaches the control module.
Read off the value.
The value must display ON when the horn is pressed. Otherwise the signal should read OFF.
Hint: The value is constantly OFF in the event of an open-circuit or a short-circuit to supply voltage. The horn value is constantly ON (horn activated) in the event of a short-circuit to ground.
Is the function OK?
Yes - Checking the output signal
No - Checking the cable for the input signal
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Checking the cable for the input signal
Check the cable between central electronic module (CEM) terminal #12D and steering wheel module (3/130) terminal #15.
Also check the ground lead for the steering wheel module (3/130) terminal #16 for an open-circuit.
If no faults are found, the fault may be in the steering wheel module.
Remedy as necessary.
Other information
- For further information about signals and other values, see Signal specification Signal Specification.
- To connect the breakout box to the central electronic module (CEM), see Connecting the breakout box Connecting the Breakout Box, Central Electronic Module (CEM).
- To connect the breakout box to the steering wheel module, see Connecting the breakout box Connecting the Breakout Box.
- To replace the steering wheel module, see Steering wheel module (SWM), replacing Service and Repair.
Continue - FAULT FOUND
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Checking the output signal
Activate the horn.
Hint: Listen for a click from the relay to determine whether the fault is in the relay circuit or in the wiring for the horn itself.
1. The horn is functioning.
2. The relay clicks.
3. The relay does not click.
1 - FAULT FOUND
2 - Checking the wiring for the horn
3 - Checking the cable for the relay
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Checking the wiring for the horn
Check the relay (2/17).
Hint: The voltage must be 12 V at terminal #3. The signal to the horn is at terminal #5.
Check the cable between relay terminal #5 and horn 1 (16/10) terminal #1 and horn 2 (16/11) terminal #1.
Also check that both the horns are grounded at terminal #2.
Check the connector.
Remedy as necessary.
Continue - FAULT FOUND
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Checking the cable for the relay
Check the cable between central electronic module (CEM) terminal #19A and horn relay (2/17) terminal #2 for an open-circuit according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.
Also check the connector for an open-circuit according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.
Hint: The fault may have been caused by an open-circuit in the supply to the relay.
The voltage must be 12 V at both terminals #1 and #2 for relay 2/17.
In particular, check that fuse 9 in the integrated relay / fusebox in the engine compartment is intact.
Try a new horn relay (2/17).
Remedy as necessary.
Other information
- For further information about signals and other values, see Signal specification Signal Specification.
- To connect the breakout box, see Connecting the breakout box Connecting the Breakout Box, Central Electronic Module (CEM).
Continue - FAULT FOUND
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