LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2007 >> STS Base, 4.6 A, AWD >> Repair and Diagnosis >> Accessories & Equipment >> Anti-Theft Systems >> Keyless Entry System And Remote Functions >> Diagnostic Information and Procedures >> DTC B3123 >> Test Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Test Description

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

  1. 2:  This step verifies that DTC B3123 is a current DTC.
  2. 3:  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. 4:  This step verifies the RCDLR is sending out the required AC voltage signal to the headliner antenna.
  4. 5:  This step verifies the RCDLR is sending out the required AC voltage signal to the console antenna.
DTC B3123

Step Action Yes No
Schematic Reference: Remote Function Schematics 
Connector End View Reference: Remote Function Connector End Views 
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle
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
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 .
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 .
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 .
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 .
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 .
Did you find and correct the condition?		 Go to Step 14  Go to Step 13 
11 Replace the RCDLR. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 Go to Step 14  -
12 Replace the headliner antenna. Refer to Ignition Lock Key Transmitter Antenna Replacement - Headliner  replacement.
Did you complete the replacement?		 Go to Step 14  -
13 Replace the console antenna. Refer to Ignition Lock Key Transmitter Antenna Replacement - Floor Console (Cup Holder)  or Ignition Lock Key Transmitter Antenna Replacement - Floor Console (Rear)  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
scientia non olet · About LEMON Manuals