For 1990-2009 cars

### Diagnostic Instructions

• | 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.

### DTC Descriptors

DTC B3121 02: Keyless Entry Antenna 3 Short to Ground
DTC B3121 05: Keyless Entry Antenna 3 High Voltage/Open

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Rear Fascia --Keyless Entry Antenna Signal | B3121 02 | B3121 05 | B3121 05 | --
Rear Fascia --Keyless Entry Antenna Signal | -- | B3121 05 | -- | --

### Circuit/System Description

The rear compartment keyless entry antenna is used to establish low frequency communications with the keyless entry transmitter. As a vehicle with a closed rear compartment lid is approached with a keyless entry transmitter, known as an user identification device, and the rear compartment lid release switch is pressed, the keyless entry antenna transmitter broadcasts a challenge to the transmitter in an approximate 1 meter range. If the response from the transmitter via radio frequency is valid, the latched rear compartment will be passively unlocked/unlatched, allowing the rear compartment area to be opened.

### Conditions for Running the DTC

The handle or touch pad used to open the rear closure is activated.

### Conditions for Setting the DTC

#### B3121 02

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

#### B3121 05

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

### Action Taken When the DTC Sets

No action is taken

### Conditions for Clearing the DTC

• | A current DTC will clear when the conditions for setting the DTC are no longer present

• | A history DTC will clear after 50 malfunction free ignition cycles

### Reference Information

#### Schematic Reference

Remote Function Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Keyless Entry System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the T10E rear compartment keyless entry antenna.
2. Ignition ON, verify a test lamp does not illuminate between the signal circuit terminal A and ground.

⇒ | If the test lamp illuminates, test the 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 AC voltage using the MIN MAX function, between the signal circuit terminal A and the low reference circuit terminal B.
4. Press the rear compartment lid release switch. Verify the DMM captured an AC voltage signal.

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

5. If all circuits test normal, test or replace the T10E rear compartment keyless entry antenna.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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