EI07279 - Horn Inoperative from Steering Wheel Horn Pad (Engineering Information)

This bulletin is being revised to update the diagnostic steps. Please discard Corporate Bulletin Number 07-08-54-001A (Section 08 -- Body and Accessories)

Important:  If the horn does not work from the key fob horn button, disregard this bulletin and proceed with diagnosis/repair according to SI.

Some customers may comment that the horn is inoperative from the horn pad on the steering wheel.

GM Engineering is attempting to find the source of an open in the ground path through the steering column.

GM has a need to obtain information DURING diagnosis. Perform the following inspection/steps:

1. Does the horn work by depressing the button(s) on the key fob?

•	Yes -- proceed with step 2.

•	No -- do not proceed with this bulletin - diagnose and repair using information found in SI.

2. Depress the horn pad to see if the horn works.




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Yes -- Disconnect the wiring harness from the horn assembly and insert appropriate connectors to monitor the voltage with a multi-meter (refer to illustration - 1). Rotate the steering wheel to one extreme of rotation. Depress the horn pad while rotating the steering wheel to the opposite extreme of rotation. Note any steering wheel position in which the horn voltage drops to zero. Proceed to step 3.

•	No -- proceed with step 3.

Caution :  When performing service on or near the SIR components or the SIR wiring, the SIR system must be disabled. Refer to SIR Disabling and Enabling. Failure to observe the correct procedure could cause deployment of the SIR components, personal injury, or unnecessary SIR system repairs.

3. Remove the Inflatable Restraint Steering Wheel Module using the procedure found in Service Information. Does the horn have output voltage when the horn contacts are depressed?

•	Yes -- Proceed with step 4.

•	No -- Verify that there are no steering wheel positions where the horn has output voltage and proceed to step 5. If the horn works in spots, go to step 4.

4. Rotate the steering wheel from extreme to extreme, testing horn operation continuously through the rotation to see if a dead spot can be found. Are any dead spots present?

•	Yes -- note the fact that inop condition is steering wheel position sensitive on the repair order. Proceed with step 5.





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No -- If the customer concern cannot be duplicated, remove the airbag module, check the resistance using a DVOM between the turn signal cancel cam and the point where the red wires attach to the horn contacts. Move the white plastic plunger that surrounds the red wires of the horn contacts to see if the plunger or the red wires can be positioned so that there is a resistance of 400 ohms or more. If so, replace the horn contacts and cancel cam. Parts will be requested through the WPC process. If the resistance checks less than 500 ohms, twist the white plunger a quarter turn to remove it. Inspect the plunger to see if a visible brown coating is present (see illustration - top example). If a visible coating is present, replace the horn contacts and cancel cam. Parts will be requested through the WPC process. If no visible coating is present, or parts have been replaced, proceed to step 16.

5. Remove the steering column trim covers. Position the steering wheel on a dead spot. Ground a test light to the steering column frame close to the steering wheel. Probe the surface of the turn signal cancel cam with the test light. Does grounding it give horn output voltage?

•	Yes -- proceed with step 8.

•	No -- proceed with step 6.

Turn Signal Cancel Cam:




6. Disconnect the wiring harness that goes to the top of the multi-function switch (connector X1). Probe the harness connection for pin G. Does this produce horn output voltage?

•	Yes -- proceed to step 7.

•	No -- Try grounding the test light on the brake pedal frame. If this produces horn output voltage, proceed to step 9. If not, proceed to step 16.

7. Replace the turn signal multi-function switch and cancel cam. Parts will be requested to be returned through the GM Warranty Parts Center process.
8. Probe the end of the red wires on the horn contacts with the test light that is grounded to the steering column frame. Does this produce horn output voltage?

•	Yes -- Check for corrosion/contamination on the contact surfaces of the contacts embedded in the steering wheel. Proceed to step 16.

•	No -- Replace the horn contacts and turn signal cancel cam. Parts will be requested to be returned through the GM Warranty Parts Center process. Proceed to step 16.

9. Remove the left side IP insulator (refer to Instrument Panel Insulator Panel Replacement found in SI) so it can be moved aside enough to see the steering column.
10. Depress the horn contacts in the steering wheel. Does the horn work?

•	Yes -- proceed to step 16.

•	No -- proceed to step 11.

Horn Clip:




11. Inspect the steering column through the insulator panel location. Note: The shaft from the steering wheel comes through a metal bracket. That bracket is surrounded by plastic, which is inside of another metal bracket. Look for a small metal clip (refer to graphic above) that connects the inner bracket (inside the plastic) and the outer bracket. Is the clip present?

•	Yes -- proceed to step 12.

•	No -- note the missing clip on the repair order. Proceed to step 15.

12. Without touching the clip, use a test light or ammeter to jumper between the red wires on the horn contact and the outer bracket on the steering column. Does the horn work when the jumper touches the outer bracket?

•	Yes -- Remove the small clip and inspect for signs of corrosion and note findings on the repair order. Clean off any corrosion and reinstall the clip. Proceed to step 13.

•	No -- Proceed to step 14.

13. Does the horn work when the horn contact is depressed?

•	Yes -- note on the repair order and proceed to step 16.

•	No -- proceed to step 14.

14. Jumper between other grounded points and the red horn wire. Does the horn work when jumpered to another ground?

•	Yes -- note which ground enabled the horn to work. Proceed with step 15.

•	No -- refer to "Horn Inoperative" section in SI to diagnose which component in the circuit is causing the horn inop. Note on the repair order and make the necessary repairs. Proceed to step 16.

15. Complete the following steps to add a ground strap between the mounting bolts of the steering column.

Steering Column Support Assembly:





15.2.

Refer to item number 2 in the graphic. This graphic shows the column support assembly. A closer look will reveal the four mounting holes of the column support assembly.

Important:     •  If a grounding strap cannot be obtained locally, one can be made by obtaining two eyelets that match the size of the column support bolts or studs and a 12 gauge (3.0 mm) wire. Cut the wire to the length needed in order to complete the circuit.    •  Some model year vehicles switched to column bracket and/or mount that may be isolated by rubber. It may be necessary to locate an alternate location to secure the ground wire to the column or column bracket in order to complete the circuit.

15.3.

Add one (1) grounding strap from the column mount (use only one of the two upper mounting holes) to one of the two lower mounting holes in the steering column support assembly or other more appropriate grounding location from step 14.

15.4.

Proceed with step 16.

16. Contact the engineer (M-F 8:00 a.m. -- 5:00 p.m. eastern time) Dave Orth (248-676-1878) to provide diagnostic results. If the engineer is not available to take the call, fax the front and back of the completed repair order to:

-	Attention: Dave Orth

-	Fax #: 248-685-6140

For vehicles repaired under Engineering direction, use: