GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 DTC 🢒 DTC B3123

Circuit Description

The headliner and console antennas are located in the rear headliner area and in the center console. They are used as a short range low frequency (LF) antennas. The headliner and console antennas are used to determine transmitter placement within the vehicle. When a valid keyless entry transmitter is within the passenger compartment, the headliner and console antennas broadcast a challenge within the passenger compartment to the transmitter. If the response from the transmitter via radio frequency (RF) is a valid response, the antenna will determine there is a fob within the vehicle. If no response is received, the antenna determines that no fob is in the vehicle.

The headliner and console antennas share a driver within the remote control door lock receiver (RCDLR) and are wired in parallel. The RCDLR has no way to determine which antenna is receiving a valid response from a transmitter, only that a valid response is being received.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3123 Keyless Entry Antenna 5&6 Performance

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC Symptom

DTC Symptom Descriptor

02

Short to Ground

Conditions for Setting the DTC

The RCDLR will set this DTC during antenna activation if the headliner and console antenna is open, shorted to battery, or shorted to ground. The RCDLR can only set a DTC when the vehicle system voltage is between 9-16 volts.

Action Taken When the DTC Sets

The RCDLR will set and store a DTC B3123.

Conditions for Clearing the DTC
    • The RCDLR no longer detects an open, a short to power, or a 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. This step verifies that DTC B3123 is a current DTC.

    2.

  2. This step tests the function of the headliner antenna. Because the console antenna and headliner antenna share a drive within the RCDLR, the console antenna must be disconnected to properly check functionality of the headliner antenna.

    3.

  3. This step verifies the RCDLR is sending out the required AC voltage signal to the headliner antenna.

    4.

  4. This step verifies the RCDLR is sending out the required AC voltage signal to the console 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 transmitter 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 B3123 as a current DTC?

Go to Step 3

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

3

Important: The ignition start button must be pressed to produce the voltage pulse to the passive antenna.

  1. Disconnect the console antenna at the center console.
  2. With the keyless entry transmitter held near the headliner antenna, press the ignition start button.

Does the vehicle start?

Go to Step 5

Go to Step 4

4

Important: 

   • The voltage signal sent by the RCDLR to the passive antenna is an A/C voltage signal. The DMM must be set on A/C voltage setting to record the voltage pulse to the passive antenna.
   • Use a DMM to record the voltage pulse using the MIN MAX setting to capture the A/C voltage pulse to the passive antenna.
   • The ignition start button must be pressed to produce the voltage pulse to the passive antenna.

  1. Disconnect the headliner antenna.
  2. With the DMM measure/capture for an A/C voltage signal between the keyless entry signal circuit and the low reference circuit.
  3. Press the ignition start button.

Was an A/C voltage signal captured on the DMM?

Go to Step 9

Go to Step 6

5

Important: 

   • The voltage signal sent by the RCDLR to the passive antenna is an A/C voltage signal. The DMM must be set on A/C voltage setting to record the voltage pulse to the passive antenna.
   • Use a DMM to record the voltage pulse using the MIN MAX setting to capture the A/C voltage pulse to the passive antenna.
   • The ignition start button must be pressed to produce the voltage pulse to the passive antenna.

  1. With the DMM, measure/capture for an A/C voltage signal between the console keyless entry antenna signal circuit and the low reference circuit.
  2. Press the ignition start button.

Was an A/C voltage signal captured on the DMM?

Go to Step 10

Go to Step 7

6

Test the headliner keyless entry antenna signal circuit and low reference circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 8

7

Test the console keyless entry antenna signal circuit and low reference circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 8

8

Inspect for poor connections at the 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 14

Go to Step 11

9

Inspect for poor connections at the headliner antenna. 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 14

Go to Step 12

10

Inspect for poor connections at the console antenna. 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 14

Go to Step 13

11

Replace the RCDLR. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 14

--

12

Replace the headliner antenna. Refer to Remote Control Door Lock and Theft Deterrent Receiver Replacement .

Did you complete the replacement?

Go to Step 14

--

13

Replace the console antenna. Refer to Remote Control Door Lock and Theft Deterrent Receiver Replacement .

Did you complete the replacement?

Go to Step 14

--

14
  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