C4 Keyless Entry and Alarm Repair, Part 1 - Technically Speaking

James Berry Sep 1, 2011 0 Comment(s)
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Q: The Passive Keyless Entry (PKE) system and alarm on my '96 C4 don't seem to be working properly. I was talking to some other Corvette owners at a car show recently, and they thought my PKE unit itself might be defective, since my key fob works fine. I would like to repair the system myself, since my local dealer wants more than $100 just to look at the car. Can you tell me where the PKE unit is located? Also, do you know if replacing it is a pretty straightforward job?

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- DeWayne
Via the Internet

A: All '93-'96 Corvettes were factory-equipped with Passive Keyless Entry. Let's start with a general overview on how the car's Universal Theft Deterrent System (UTD) works. This system provides an audible warning using the vehicle's horns in the event of an unauthorized entry through either door or the hatch. If such an entry is detected, the PASS-Key (Personalized Automotive Security System) and FEDS (Fuel Enable Data Stream) system will disable the vehicle by not allowing the engine to crank and preventing fuel from being delivered to the injectors.

Although a separate system, PKE is a vital part of the car's theft-deterrent strategy. The system has two modes: passive and manual. The passive mode allows the doors to lock and unlock as you walk toward or away from the vehicle. The manual mode allows you to unlock the doors as you would with any other key fob. However, to set the alarm in the manual mode, you'll need to manually lock the doors using either the auto lock on the door or the key.

In the passive mode, the PKE receiver senses the transmitter located in the fob and automatically locks or unlocks the doors at a preset distance from the car. (Even in this mode, the user also has the capability to manually operate the door or hatch lock by pushing the corresponding button on the transmitter.) The transmitter sends out unique digital identification and operation codes that are only recognized by its corresponding receiver.

When the transmitter is in close enough proximity to the receiver, the two will be in constant communication to determine where the transmitter is and how to respond. Once the transmitter is out of range, the system waits five seconds, locks the doors, arms the UTD system, and beeps the horn.

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Replacing the PKE Transmitter Battery
If your transmitter isn't working, the first thing to check is the transmitter battery. Let's go over the process of replacing it.

1. Insert a pocket screwdriver or dime-size coin into the slot on the back of the transmitter and gently pry apart the two halves.
2. Gently pull the battery out of the transmitter and then clean the inside of the transmitter with a spray contact cleaner. This procedure is similar to cleaning the mouse on your home computer.
3. When replacing the battery, inspect the transmitter for broken prongs. This is a common failure with Corvette transmitters.
4. Put the new battery in the transmitter; use a CR2032-type or equivalent. The battery is held in place by two retaining clips and can be difficult to install. The easiest method is to hook it into the bottom retaining hook first and then press it into the top hook.
5. Reassemble the transmitter.
6. Test the transmitter.

A weak battery will cause the range at which the PKE operates to be reduced. If you have noticed that you need to be closer to your vehicle for the transmitter to function, it's possible that the battery is getting weak.

Replacing the battery in your transmitter will not require the transmitter to be reprogrammed to the PKE receiver. However, a new transmitter or any additional transmitters will need to be programmed.

Programming the PKE Transmitter
The PKE system is capable of using three different transmitters, each with its own distinctive Vehicle Access Code (VAC). The transmitter-programming mode is initiated by entering a specific button sequence on the Driver Information Center (DIC), located on the center console (Image A). Use the following steps to enter the programming mode:

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1. Move the transmitters to be programmed 12 to 15 feet away from the car.
2. Turn the ignition to the Run position, engine off.
3. Push the Trip Odometer button once and release (Image B).
4. Push the Trip Odometer button again and hold for five seconds.
5. Within five seconds push and hold the Fuel Information button for 10 seconds, until the Passive Keyless Entry lamp illuminates constantly (Image C).
6. Turn the key to the locked position with the key remaining in the ignition. The Passive Keyless Entry lamp should flash once per second, signaling that the system is ready to program the first transmitter. The number of times the light flashes corresponds to the number of the transmitter you're programming—once per second for the first transmitter, twice per second for the second, and three times per second for the third.
7. Bring the transmitter to be programmed into range.
8. The Passive Keyless Entry light will come on and stay on, signaling that the code has been stored.
9. Move the transmitter out of range. The system light will flash again, demonstrating that the system is ready for the next transmitter.
10. The programming mode can be exited by removing the key from the ignition or by turning the ignition on.

A few things to note: Turning off the programming mode before you program any transmitters will not cancel any transmitters that previously have been programmed. Bringing more than one transmitter into range at a time will make it difficult for the system to search for individual codes. The programming mode will automatically shut off after two minutes if no transmitters have been programmed, or if the key is removed.

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Enabling the Passive Unlock/Lock
The passive unlock/lock disable procedure allows you to turn off the passive function of the PKE system. To do this, perform the following steps:

1. First, a transmitter must be in range of the PKE receiver.
2. The key must not be in the ignition.
3. Push the door-lock switch for approximately five seconds (Image D).
4. The PKE module will lock and then unlock the doors to verify that the command has been sent.
5. When the passive feature has been disabled, the Passive Keyless Entry lamp will not illuminate when the key is first turned on (before the vehicle is started).

If the passive feature has been disabled, simply repeating the procedure above will enable it again. The Passive Keyless Entry lamp will then illuminate when the key is first turned on.

Programming One or Both Doors to Unlock in Passive Mode
The system allows you to choose whether you want the passenger door to unlock passively. (The PKE will always unlock the driver's door when the system is in the passive mode.) To enable or disable the passenger door, perform the following procedure:

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1. First, a transmitter must be in range of the PKE receiver.
2. The key must be in the ignition in the off position.
3. Push the door-lock switch for approximately five seconds.
4. The PKE module will then lock and unlock the doors to verify that the command has been sent.

Even if the driver-door-only unlock option has been chosen, you can still unlock the passenger door using the transmitter.

Arming the Alarm
Let's go over how to run a simple test on your Corvette's theft-deterrent system:

1. Lower the driver-side window before turning off the vehicle.
2. Open the door with the ignition in the off position; the Security light should flash. This flashing light is your cue to arm the security system.
3. To arm the system, open the door.
4. With the door open, lock the door using the power door-lock switch or the transmitter (Image E). The Security light should come on. If you lock the vehicle with the manual door lock or the key, the system will not arm.
5. Close all of the doors. The Security light should go off, indicating that your system is armed.

Testing the Alarm
Now that your alarm is armed, you can test it for proper operation by doing the following:

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1. After arming the system (as described above), wait approximately 10 seconds.
2. Reach inside the open window, unlock the door using the manual door lock, and open it using the inside handle. The alarm should go off.
3. The alarm should sound for approximately three minutes; it then will go off to save battery power. Even though the alarm may not be sounding, the vehicle will not start until the system is deactivated.
4. If the alarm did not go off, make sure your horns are working; it's possible that you have a blown horn fuse or a defective horn.

Turning Off the Alarm
In the event you accidentally set off your C4's alarm, you can turn it off by following these steps:

1. Unlock the door with your key.
2. Put the key in the ignition and turn it to the Run position.
3. Use the fob to deactivate the alarm.

As you can see, there's a lot to learn when it comes to the PKE system in your C4. Fortunately the system is not complicated once you understand how it works. If your transmitters will not program, or your PKE system is not working, it's time to perform some diagnostics. Next month we'll cover these procedures, along with component location and PKE-receiver repair. vette

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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