GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 XLR 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC B3121

Circuit Description

The Keyless Entry Antenna-Rear Compartment is located in the lower rear compartment area near the latch and is used as a short range Low Frequency (LF) transmitter. As a vehicle with a closed rear compartment lid is approached with a Key Fob and the exterior deck lid handle switch is pressed, the Keyless Entry Antenna transmitter broadcasts a challenge to the Key Fob in an approximate one-meter rang. If the response from the Key Fob via radio frequency (RF) is valid, the latched rear compartment will be passively unlocked/unlatched, allowing the rear compartment area to be opened.

Conditions for Setting the DTC

The Remote Control Door Lock Receiver (RCDLR) will set this DTC during antenna activation if the Keyless Entry Antenna-Rear Compartment is Open, shorted to battery or shorted to ground and an authentication occurs. The (RCDLR) can only set a DTC when it is the vehicle system voltage is between 9-16 volts.

Action Taken When the DTC Sets

The Remote Control Door Lock Receiver (RCDLR) will set and store a DTC B3121.

Conditions for Clearing the DTC
    • The Remote Control Door Lock Receiver (RCDLR) no longer detects a open, short to power or short to ground on the antenna circuit.
    • The use of a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Verifies that DTC B3121 is a current DTC.

    2.

  2. Testing for power and ground to the Keyless Entry Antenna.

Step

Action

Yes

No

Schematic Reference: Keyless Entry Schematics

Connector End View Reference: Keyless Entry Connector End Views

1

Did you perform the Diagnostic System Check-Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Important: To achieve service by pass mode (key ON engine OFF) A programmed Key Fob must be detected within the passenger compartment of the vehicle.

  1. Install a scan tool.
  2. Push and hold the ACC button for 5 seconds to achieve the service bypass mode, with the engine OFF.
  3. Select display DTCs function on the scan tool in the Remote Control Door Lock Receiver (RCDLR) menu.

Does the scan tool display DTC B3121 as a current DTC?

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3

Important: The voltage signal sent by the RCDLR to the passive antenna is a AC voltage signal. The DMM must be set on AC voltage setting to record the voltage pulse to the passive antenna.

Important: Use a DMM to record the voltage pulse using the MIN MAX setting to capture the AC voltage pulse to the passive antenna.

Important: The exterior rear compartment pad must be pressed to produce the voltage pulse to the passive antenna.

  1. Disconnect the Keyless Entry Antenna-Rear Compartment at the Rear Compartment latch area.
  2. With the DMM measure/capture for an AC voltage signal between the Keyless Entry Antenna power circuit and the ground circuit.

Was an AC voltage signal captured on the DMM?

Go to Step 6

Go to Step 4

4

Test both the Keyless Entry Antenna power and ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 5

5

Inspect for poor connections at the Remote Control Door Lock Receiver (RCDLR). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 7

6

Inspect for poor connections at the Keyless Entry Antenna-Rear Compartment. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 9

7

Test the Keyless Entry Antenna power circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 8

8

Important: When replacing the Remote Control Door Lock Receiver (RCDLR) refer to Programming Theft Deterrent System Components in Theft Deterrent.

Replace the Remote Control Door Lock Receiver (RCDLR) . Refer to Remote Control Door Lock Receiver Replacement .

Did you complete the replacement?

Go to Step 11

--

9

Test both the Keyless Entry Antenna power and ground circuit for a short to power. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 10

10

Replace the Keyless Entry Antenna-Rear Compartment. Refer to Ignition Lock Key Transmitter Antenna Replacement - Rear Compartment .

Did you complete the replacement?

Go to Step 11

--

11
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the conditions for running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 3

System OK