• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

The keyless entry system will unlock the vehicle doors or open/unlock the rear compartment when a corresponding button on the keyless entry transmitter is pressed. This is accomplished by the keyless entry transmitter sending a radio frequency to the remote control door lock receiver, which then sends the signal to the body control module (BCM). The BCM interprets the signal and activates the requested function. A low transmitter battery or radio frequency (RF) interference from aftermarket devices such as 2-way radios, power inverters, cellular phone chargers, computers, etc. may cause a system malfunction. High RF traffic areas, such as gas stations which use pay-at-the-pump RF transponders, may also cause interference that could lead to a malfunction.

The remote control door lock receiver uses the AM/FM antenna, located in the rear glass, to increase the range of the transmitter. A coax cable connects the remote control door lock receiver to the radio antenna amplifier. The radio antenna amplifier acts as an interface that combines the radio antenna and the remote control door lock receiver antenna. This allows both the radio and the remote control door lock receiver to use the AM/FM antenna.

• Unwanted or inadvertent door lock/unlock activation may be requested by the OnStar® Remote Link application. It is possible that a customer may be unaware of account usage, resulting in an unwanted or phantom door lock/unlock. If normal system diagnosis does results in an inability to verify the customer’s concern, contact Technical Assistance Center (TAC).
• Because both the remote control door lock receiver and the radio use the radio antenna amplifier to interface with the AM/FM antenna located in the back glass, any damage to the antenna or a malfunction in the radio antenna amplifier will result in both a reduction in keyless entry system range and poor reception when listening to AM/FM radio.
• If available, the EL 43241 Keyless Entry Tester may be used to diagnose a low transmitter battery or a malfunctioning transmitter. To test, place the transmitter on the test pad of the EL 43241 and press each transmitter button one at a time, holding each button for three s. If the green light on the tester does not illuminate and a tone does not sound, first replace the transmitter battery and retest. If the malfunction continues after replacing the transmitter battery, replace the transmitter.
• When using the EL 43241 Keyless Entry Tester, first inspect the keyless entry transmitter part number to determine that it is the correct model for the vehicle. An incorrect part number transmitter may pass the test, but it will not activate the keyless entry system.

Remote Function Schematics

Master Electrical Component List

Keyless Entry System Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Control Module References for scan tool information

EL 43241 Keyless Entry Tester

1. Verify that the keyless entry transmitter is correct for the vehicle. This can be accomplished by comparing the part number printed on the transmitter to the appropriate part number in the parts catalog.
• If the transmitter is incorrect

  Replace the keyless entry transmitter.

• If the transmitter is correct
2. Ignition OFF, disconnect the remote control door lock receiver coax cable from the K77 Remote Control Door Lock Receiver and from the T23 Radio Antenna Amplifier.
3. Verify the antenna coax cable passes the coax cable component test. Refer to Component Testing.
• If the coax cable does not pass the test

  Replace the antenna coax cable.

• If the coax cable passes the test
4. Connect the antenna coax cable to the K77 Remote Control Door Lock Receiver, ignition ON.
5. Test for greater than 4.5 V between the antenna coax cable center terminal and ground.
• If 4.5 V or less

  Replace the K77 Remote Control Door Lock Receiver.

• If greater than 4.5 V
6. Connect the antenna coax cable to the T23 Radio Antenna Amplifier.
7. Operate the transmitter while observing the scan tool Key Fob Function parameter for the appropriate transmitter.
8. Verify the scan tool Key Fob Function parameter corresponds with the function selected on the transmitter.
• If the Key Fob Function parameter does not correspond with the transmitter selection

Note: Before replacing the transmitter, inspect the transmitter battery contacts for any corrosion or damage. If no corrosion or damage is found, replace the transmitter battery and retest before replacing the transmitter.

1. Replace the keyless entry transmitter.
2. Operate the new transmitter while observing the scan tool Key Fob Function parameter for the transmitter.
3. Verify the scan tool Key Fob Function parameter corresponds with the function selected on the transmitter.
• If the Key Fob Function parameter does not correspond with the transmitter selection, replace the K77 Remote Control Door Lock Receiver.
• If the Key Fob Function parameter corresponds with the transmitter selection.
4. All OK.
• If the Key Fob Function parameter corresponds with the transmitter selection
9. All OK.

1. Ignition OFF, disconnect the remote control door lock receiver coax cable from the K77 Remote Control Door Lock Receiver and from the T23 Radio Antenna Amplifier.
2. Test for less than 5 Ω between the coax cable center terminals end to end.
• If 5 Ω or greater

  Replace the coax cable.

• If less than 5 Ω
3. Test for less than 5 Ω between the coax cable outer shield end to end.
• If 5 Ω or greater

  Replace the coax cable.

• If less than 5 Ω
4. Test for infinite resistance between the coax cable center terminal and the outer shield.
• If less than infinite resistance

  Replace the coax cable.

• If infinite resistance
5. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

• Remote Control Door Lock and Theft Deterrent Transmitter Programming
• Control Module References for replacement, programming, and setup