C4 Keyless Entry and Alarm Repair, Part 2 - Technically Speaking

James Berry Oct 1, 2011 0 Comment(s)
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Welcome back for the second part of our Passive Keyless Entry (PKE) system operation-and-diagnostics overview for '93-'96 Corvettes. This month we'll cover the component location, PKE diagnostics, and how to repair the PKE receiver instead of replacing it.

Vemp 1109 01 C4 Corvette Passive Keyless Entry And Alarm 2/3

Let's review how the system works. When the system is in the passive mode, the PKE receiver (located in the vehicle) senses the transmitter in your key fob and automatically locks or unlocks the doors as you walk toward or away from the vehicle. If this isn't happening, and you've exhausted all the steps in last month's column, you'll need to remove the PKE receiver for examination.

Removing the PKE Receiver
The PKE receiver can only be accessed by removing the upper dash panel. The following steps will take you through this process.

1. First, remove the negative battery cable.
2. Next, remove all three air-vent outlets. This will expose two small Torx-head screws inside each outlet. Remove these.
3. There are more fasteners hidden under the fuse panel. Detach the fuse-box cover, then locate and remove the three hex-head screws that retain the side panel.
4. Behind the side panel is a hex-head screw for the lower knee panel and dashpad. Remove it.
5. Behind the passenger vents are three hex nuts that hold the lower dashpad in place. Remove these retainers and pop off (but don't completely remove) the lower dashpad. This will allow you to access the upper-dash-pad tabs.
6. Behind the center vent are two hex-head screws holding the upper dashpad and center trim. One is located on the left, holding the dashpad, and one is on the right, holding the center trim. Remove these screws and pop out the center trim about 4 inches.
7. Behind the driver's vent is one hex-head screw holding the dashpad. Remove this.
8. Next, pop off the defroster-vent trim in the center of the dash; take care not to damage the light sensor, which is attached. Removing the defroster vent will expose two Torx screws that are attached to the dashpad. Remove these.
9. Once all the screws are removed, carefully lift up on the dashpad and pull back to release the rear dash pins from the dash-pad reinforcement frame. The entire upper dash should come out with minimal effort. If it doesn't, go back and make sure all the hidden fasteners have been removed. Some dashpads will have random spots of adhesive holding the edges in place. These glued dashes will take a little more time and patience to remove but shouldn't give you too much trouble.
10. Next, remove the instrument cluster.
11. Once the instrument cluster has been removed, look under the center A/C-vent tube, directly behind the A/C control head in the center of the dash. Here you will see two boxes. The top box is the tone-generator (chime) module, which is held in place with Velcro. You'll need to remove this module to access the PKE receiver.
12. The PKE receiver is located directly under the tone generator. The PKE receiver is also held in place with either Velcro or spring clips on the sides. Now comes the tricky part. The PKE module can only be removed in the direction of the passenger side—and it won't go easily. You'll need to tug and tweak until you can manipulate the unit out.
13. The part number for the receiver is the same for all '93-'96 Corvettes (PN 10261112) As is the case with most items for the C4, Chevrolet has discontinued it.

Checking the Fuses
The first thing to do when working with anything that may be controlled by a fuse is to test all of the related fuses with a test light. Start by turning the key to the On position. There are two places to probe on the back side of each fuse; probe them with a test light and continue this process for every fuse (Image A). If the test light doesn't light on both sides, that fuse is most likely blown. If the test light doesn't light on either side of the fuse, you'll need to look in the owner's manual to see what that circuit feeds. Certain circuits may require that you activate something to illuminate the test light—for example, by turning on the headlamp switch.

Some key fuses on C4 Corvettes are:

&bull #40 BATT 5A (provides constant power to the PKE module)
&bull #26 PKE 5A (provides 12 volts when the ignition switch is in Run position)
&bull #42 POWER LOCK (provides voltage to the indicator bulb and power-door-lock relays in the module)

How to Run a Diagnostic Test on a 12-Pin ALDL System (Image B)
Assuming your fuses check out OK, you can run a diagnostic check using the following procedure:

Vemp 1109 02 C4 Corvette Passive Keyless Entry And Alarm 3/3

1. Connect pins A and G together on the 12-pin Assembly Line Data Link (ALDL) connector. (Note that while this diagram is labeled "F-body," the procedure is the same for Corvettes.)
2. Turn the key to the Run position, engine off. The PKE light in the Driver Information Center (DIC) will flash any existing fault codes. If no fault codes flash, it's likely that you have a faulty PKE receiver.
3. The DIC light will flash once, pause, and flash again two to seven more times to indicate the existing fault code. For example, one flash followed by a pause and then two more flashes would indicate a code 12.
4. The following is a list of Diagnostic Trouble Codes (DTC) and what they mean:
&bull 12: Receiver Memory Bad
&bull 13: Transmitter Not in Range
&bull 14: Non-Valid Transmitter Received
&bull 15: Valid Transmitter Received
&bull 16: Passenger Door Button Depressed
&bull 17: Hatch Button Depressed

How to Run a Diagnostic Test on a 16-Pin ALDL System
1. Connect pins 5 and 8 together on the 16-pin ALDL connector.
2. Turn the key to the Run position, engine off. The PKE light in the Driver Information Center (DIC) will flash any existing fault codes. If no fault codes flash, it's likely that you have a faulty PKE receiver.
3. The DIC light will flash once, pause, and flash again two to seven more times to indicate the existing fault code. For example, one flash followed by a pause and then two more flashes would indicate a code 12.
4. The following is a list of DTCs and what they mean:
• 12: Receiver Memory Bad
• 13: Transmitter Not in Range
• 14: Non-Valid Transmitter Received
• 15: Valid Transmitter Received
• 16: Passenger Door Button Depressed
• 17: Hatch Button Depressed

Notes on Fault Codes
A fault code 12 likely indicates that you have a PKE receiver with an internal failure (common).

A fault code 13 likely indicates that you have transmitter with a faulty battery (common), a faulty transmitter (common), or a faulty or unplugged antenna (uncommon).

&bull Remember that inside the key fob is a tiny gold bearing located in a small cylinder. This bearing "wakes up" the PKE receiver when movement is detected. If the bearing becomes dirty, its movement may be restricted, causing the receiver to wake up sporadically or, in severe cases, not at all.
&bull It's possible to remove the metal housing and gently clean the inside with spray contact cleaner. You'll also need to clean the ball bearing; this procedure is similar to cleaning the mouse on your home computer. Be sure to use a cleaning agent that is appropriate for electrical components.

A fault code 14 likely indicates that your transmitter isn't programmed or has a defective battery (common).

A fault code 15 likely indicates that you have a system input that isn't in a ready state. You'll need to test all of the system inputs to determine which one is at fault (see below). If no input faults are found, you most likely have a PKE receiver with an internal failure.

&bull If the key-in-ignition switch isn't working correctly, the PKE system will not operate. This feature is intended to prevent the system from auto-locking if you accidentally leave the key in the ignition. If the system is functioning correctly, the programmed door or doors will remain unlocked when the key is left in the ignition. Verify that you haven't accidentally left the secondary transmitter in the vehicle.
&bull To verify your that key-in-ignition switch is working, open the driver's door with the key inserted in the ignition and listen for the warning chime.
&bull If no chime is heard, you either have a defective key-in-ignition switch in the steering column or there is a wiring problem between the ignition switch and the CCM module or PKE receiver. It's also possible that the CCM module or PKE receiver is defective.
&bull To test for an intermittent open circuit within the steering column, actuate the tilt-steering-wheel mechanism while the key is in the ignition and listen for the chime. If you hear the chime while actuating the steering column, you have an open circuit in the column.
&bull You can also test for an intermittent open circuit at the key-in-ignition switch by wiggling the ignition key and listening for the chime. If you hear the chime while wiggling the key, you have a faulty switch.

A fault code 16 likely indicates that you have a malfunctioning or misadjusted door switch (common).

A fault code 17 likely indicates that you have a faulty transmitter (common). If you have two transmitters, bring your secondary transmitter into range, shake it, and see if the fault goes away. If so, your primary transmitter is faulty.

Repairing Cold Solder Joints in the PKE Receiver
Intermittent problems with electronic modules or circuit boards are often the result of a cold solder joint. Cold solder joints are quite common in remote-keyless-entry fobs and PKE receivers, as well as a multitude of other modules on Corvettes.

The term "cold solder joint" refers to a solder connection that wasn't heated enough during manufacturing, was cooled too quickly, or had its component pins moved before the solder had a chance to solidify. With time, cold solder joints can become problematic due to vibration, repeated thermal cycling, or constant exposure to high temperatures.

When diagnosing a bad solder joint, try tapping on the suspect component. If this causes it to work temporarily, you'll have a pretty good indication that you've found the problem. For example, when trying to determine why the PKE receiver would not automatically lock or unlock our C4's doors when the transmitter was in range, we found that tapping the top of the receiver briefly rectified the glitch. This led us to deduce that the PKE receiver was the culprit.

You can repair cold solder joints without knowing anything about circuitry. Use a light and a magnifying glass to examine components for hairline cracks in the solder around the pins. Fixing them will require a low-wattage, pencil-style soldering iron and some rosin-core solder, which can be found at any Radio Shack or auto-parts store.

Apply a small amount of solder to the heated iron, and then use the tip of the iron to heat the joint and apply the solder at the same time. The solder should flow evenly on the joint, repairing the connection. This process should only take a second or two. Any more, and the heat from the iron could damage the circuit board or the component itself. Repeat as needed, soldering any and all questionable connections.

Don't be afraid to try this simple repair on your Corvette's PKE. Remember, the components in question are already broken and would otherwise be discarded.

As we mentioned earlier, the C4 PKE receiver has been discontinued by GM. So if you can't repair yours, you have the option of either buying a salvage-yard replacement or sending it out to be rebuilt. If you choose the rebuild route, be sure to give the rebuilder a detailed list of your symptoms. This will help him verify that the repair has been completed before returning the unit to you. Vette

When diagnosing a bad solder joint, try tapping on the suspect component. If this causes it to work temporarily, you'll have a pretty good indication that you've found the problem.

Questions?
Got a question for our Tech Corner expert? Just jot it down on a paper towel or a lightly soiled shop rag and send it to us at VETTE Magazine, Attn: Technically Speaking, 9036 Brittany Way, Tampa, FL 33619. Alternatively, you can submit your question via the Web, by emailing it to us at vette@sorc.com. Be sure to put "Technically Speaking" in the subject line.

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