Do you have a C5 with a horn that no longer functions, or worse, one that blows continuously? Your local GM dealership will probably provide you with a quote of $900+ for an airbag assembly to remedy the problem. That’s a lot of money to fix a horn!
Testing for a malfunctioning horn switch begins at the underhood electrical center. Locate and remove the horn relay for circuit testing. A 12 volt test light will be used for testing. You cannot damage any of the horn components (including the horn switch in the air bag) when using a test light in this manner, whether the test lead is on battery power or ground. Connect your test light lead to a good ground (the battery is the best place). The horn relay has four terminals; you should find that two of the four horn relay socket terminals have a bright light (battery voltage) during testing. Now the test light lead is placed on the battery’s positive terminal for the next test. When probing the remaining two horn relay socket terminals, you should find one that will illuminate the test light when the horn button is pushed. This is the relay control wiring coming from the horn switch. If you cannot get the test light to illuminate when pushing on the horn button in one of the two remaining socket terminals, the horn switch is the most likely problem. The remaining socket terminal should light dimly as it feeds low voltage current to the horns themselves. If the socket terminal does not illuminate your test light dimly, the horns have an open circuit (horns are bad).
Keep in mind that the wiring from the horn switch to the relay could have an open circuit which will require you to access the horn wiring below the dash. You would have to locate connector C209 at the steering column. C209 has 23 cavities; you would need to find the black wire in position V. When the horn switch is pushed a test light connected to battery power should light up with the test light probe in connector position V. We have also found the connector under the airbag for the horn switch broken with the wire hanging loose. In most cases further steering column work is required to replace the cancel cam that the horn switch wiring locks into.
The horn switch itself is a high tech membrane switch that consists of two thin plastic sheets with what appears to be a copper viscous paste. Over time the copper viscous fluid shorts out, the horn switch contacts close, and then the horn keeps sounding. Another common problem is the membrane switch will not close the circuit and the horn will not blow. Corvette Central has the correct replacement switch ready to install with the required wire leads. Corvette Central’s item number 565100 is at a considerably lower cost than the complete air bag assembly. The tricky part is that the membrane switch is part of the air bag assembly sandwiched between the cover and the air bag itself.
IMPORTANT SAFETY TIPS
- The air bag system is powered up for an extended period of time after the battery is disconnected with a Sensing Diagnostic Module (SDM). Even though you may have disconnected the battery, air bag deployment is possible up to 10 minutes after the battery has been disconnected.
- Static electricity can also deploy the air bag. Replacing the switch on a crisp, dry, cold morning can be dangerous. GM uses a shorting bar on the air bag connector to alleviate the possibility of static electricity deployment. Make sure the air bag assembly is on a non-conductive surface and avoid the connector terminals.
- GM suggests that the ignition key be removed as well as fuse number 16 from the fuse panel for SDM power. The panel below the steering column is removed next to access the air bag yellow two-wire connector. All air bag wiring has a yellow sheath to denote it is part of the Supplementsl Inflatable Restraint System (SIRS). Remove the connector lock and disconnect the two-wire connector.
- Do not work directly over the air bag at any time. Set the assembly aside in an open area once the cover is removed.
- Extreme caution must be taken any time an air bag is handled. Make sure that you have grounded your hands on a metal object to release any static electricity before handling the assembly.
The tricky part is that the horn cover has to be removed from the air bag so the switch can be installed into the cover. We removed the air bag assembly then brought the cover over to our bench. First, the air bag fascia cover must be removed, and then the switch is replaced. Admittedly, it is a bit unnerving to see the air bag folded up in place when the horn fascia cover is removed. Installing the switch into the cover was not too difficult with some careful plastic trimming. The membrane switch was slid into place and the cover reassembled.
Over time, C5 Corvette horn switches will fail. If you have any trepidation at all about working with an air bag, it is recommended that you consult a professional.
Here we are testing the horn relay connector terminals. This is the correct terminal to test the horn membrane switch. Our test light illuminates with the test light lead on the battery positive post and the relay terminal as shown. The two terminals to the left of the terminal tested should have battery voltage.
The airbag assembly comes off after removing the two T-30 Torx screws from the backside of the steering wheel. The T-30 bit must be at least an inch and a half long to reach the screws.
The yellow connector has to be removed by pulling the connector straight out. These two gold pins inside the air bag module should be covered with tape to prevent accidental static electricity from activating the air bag.
Now the red horn wire connector is twisted counterclockwise to release the connector. Care must be used when removing and installing this connector where it locks into the turn signal cancel cam. The cancel cam has a small plastic leaf that can be easily broken.
Four ten-millimeter nuts are removed to release the horn cover retainer.
Corvette Central sells this horn contact membrane for C5 Corvettes. Item # 565100.
We trim the rubber away that was heat sealed to retain the membrane switch backing plates. The rubber from both backing plates is trimmed on the inside to slip the switch out.
The backing plates are lifted up off the rubber on both sides. Care must be taken to avoid breaking the backing plates.
The new membrane switch is sandwiched under the white plastic retainer and some plastic welding secures the retainer back in place.
The cover is ready for installation on the air bag assembly. The air bag can deploy if static electricity or any electrical charge touches the yellow connector so be sure to avoid and cover the connector until it is ready for installation. This should not be done by a novice; the airbag must be respected to avoid injury.
Story and photos courtesy Chris Petris