Cruze

DTC B3121

The rear fascia aerial is located in the rear fascia assembly and is used to establish low frequency communications with the keyless entry transmitter. As a vehicle with locked doors is approached with a keyless entry transmitter and the exterior rear closure touch pad is pressed, the keyless entry control module communicates with the rear fascia keyless entry aerial.

B3121 02

The keyless entry control module detects a short to ground on the rear fascia keyless entry aerial circuit.

B3121 05

The keyless entry control module detects a short to B+ or an open on the rear fascia keyless entry aerial circuit.

Rear closure will not open when rear closure touched pad is pressed.

Schematic Reference

Remote Function Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Keyless Entry System Description and Operation : with ATH → without ATH

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Note: Verify that the pins are correct for all of the aerials. Make sure to fix any problems with the interior aerials first, before proceeding to the following diagnostics below regarding the exterior aerials. If any of the interior aerial DTCS B3122, B3123, B3124 is set, the diagnostic procedures on the exterior aerials will not work.

1. Ignition OFF, disconnect the harness connector at the T10G rear fascia aerial.
2. Ignition ON, verify a test lamp does not illuminate between the signal circuit terminal 1, connector on vehicle side, and vehicle ground and also does not illuminate between low reference signal circuit terminal 2, connector on vehicle side, and vehicle ground.

⇒	If the test lamp illuminates, disconnect the connector at the keyless entry control module, test the appropriate signal circuit for a short to voltage. If the circuit tests normal, replace the keyless entry control module.

3. Connect a DMM, set to capture DC voltage using the MIN MAX function, between the signal circuit terminal 1 and vehicle ground.

Note: Use DC voltage because comparing to vehicle ground.

4. Activate the rear fascia aerial by manually pressing the rear closure touch pad. After hitting the min/max button looking for any voltage, verify the DMM captured a DC voltage signal.

⇒	If the DC voltage was not captured, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the keyless entry control module.

5. Connect a DMM, set to capture DC voltage using the MIN MAX function, between the low reference circuit terminal 2 and vehicle ground.
6. Activate the rear fascia aerial by manually pressing the rear closure touch pad. After hitting the min/max button looking for any voltage, verify the DMM captured a DC voltage signal.

⇒	If the DC voltage was not captured, test the low reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the keyless entry control module.

7. Clear DTCs then press the rear closure touch pad and check for DTCs again.

⇒	If DTC B3121 returns replace the T10G rear fascia aerial. Clear DTCs again then press the rear closure touch pad and check for DTCs.

⇒	If DTC B3121 returns, replace the keyless entry control module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for keyless entry control module replacement, setup, and programming