Horn - Inoperative When Pressing Horn Pad
TECHNICALBulletin No.: 07-08-54-001C
Date: October 17, 2008
Subject:
EI07279 - Horn Inoperative from Steering Wheel Horn Pad (Ground Path Repair Procedure)
Models:
2006-2007 Buick Rainier
2006 Chevrolet TrailBlazer EXT
2006-2009 Chevrolet TrailBlazer
2006 GMC Envoy XL, Envoy XUV
2006-2009 GMC Envoy, Envoy Denali
Supercede:
This bulletin is being revised to provide field fix information. Please discard Corporate Bulletin Number 07-08-54-001B (Section 08 - Body and Accessories).
Condition
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.
Cause
The general cause of this condition is high resistance in the ground path through the steering column that energizes the horn relay. The key fob panic button uses a different ground path and is not affected. A number of locations in the circuit have been identified as sources of the high resistance. It is often difficult to pinpoint the specific location of the high resistance because the condition is usually intermittent. Attempting to discover the location can be frustrating because as circuit components are moved, the condition will often disappear. A few locations have been identified as frequent contributors to the problem.
Correction
Complete the following steps to diagnose and repair this condition:
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. To aid in the diagnosis and to avoid disturbing others, disconnect the wiring harness from the horn assembly and insert appropriate connectors to monitor the voltage with a multi-meter or a test light. If the horn pad is currently working, rotate the steering wheel lock to lock while depressing the horn pad to determine if there are any spots in the rotation where the horn pad quits working.
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. Remove the horn contacts from the steering wheel. Clean the brass contact on the end of the red wires with an abrasive pad. If possible, remove any contamination present on the mating contact on the cancel cam (inside the black tube). Also clean the four copper rivets embedded in the steering wheel frame. Apply GM Dielectric Lubricant to all the contacts to protect against reoccurrence of the corrosion. Refer to the graphic.
4. Reinstall the horn contacts and the Inflatable Restraint Steering Wheel Module and test for proper operation of the horn pad. Test for proper operation of the horn pad through the entire steering wheel rotation. Does the horn pad work properly?
^ Yes - repair is complete.
^ No - proceed with step 5.
5. Is the inoperative condition only present at certain steering wheel positions?
^ Yes - proceed with step 6.
^ No - proceed with step 9.
6. 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 the cam activate the horn?
^ Yes - this may mean that the contact of the cancel cam that mates to the horn contact wiring harness contact, may not be clean enough or that the cancel cam may need to be replaced. Repair as necessary. Procedure complete.
^ No - proceed with step 7.Turn Signal Cancel Cam:
7. Disconnect the wiring harness that goes to the top of the multi-function switch (connector X1). Using the grounded test light, touch the harness connection for pin G. Does grounding the pin activate the horn?
^ Yes - proceed with step 8.
^ No - try grounding the test light on a known good ground. If this activates the horn, proceed to step 9. If not, investigate a possible condition with the wiring harness or BCM with appropriate SI documents.
8. The condition lies either in the multi-function switch or the interface between the multi-function switch and the cancel cam. In some cases, removing the multi-function switch and clearing the horn contact that mates with the cancel cam (refer to the graphic) of debris and reinstalling the switch will eliminate the condition. In other cases, the cancel cam may be losing contact with the multi-function switch contact. If distortion in the cancel cam is present, it may be necessary to replace the cancel cam. Repair as necessary. Procedure complete.
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 - Check if the operation of the horn is sensitive to pressure applied to the steering wheel as if a driver were doing a panic stop. In some cases, pressure applied to the steering wheel in different directions will expose a bad ground path in the steering column. Proceed to step 11.
^ No - proceed with step 11.
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 the "horn clip" graphic) that connects the inner bracket (inside the plastic) and the outer bracket. This clip provides an auxiliary ground path which is needed in some cases, if the primary path has a bad connection.
12. To verify this, connect a test light between the red wire on the horn contacts in the steering wheel and the steering column sections (1) and (2) in the illustration. Does the horn work when grounded to (1) and not (2)?
^ Yes - add or replace the horn clip.
^ No - refer to the Horn Inoperative section in SI to diagnose which component in the circuit is causing the horn inoperative condition.
Parts Information
Warranty Information
Disclaimer