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.

### Circuit/System Description

AM and FM radio reception is dependent on the following components:

• | Radio antenna

• | Coax cable between the radio antenna and the radio antenna module

• | Radio antenna module

• | Coax cable between the radio antenna module and the radio

• | Radio

### Diagnostic Aids

Poor AM and FM radio reception is dependent on multiple influences, some of which may not be vehicle related. Areas which have high RF traffic or block the signal path may cause a degradation in radio reception. Radio reception may also be influenced by items within the vehicle, but not part of the radio system. Such examples are aftermarket electrical accessories or other items which may generated noise in the vehicle electrical system. Aftermarket window tinting, especially when there is a metallic in the film, may reduce radio reception.

For the Diversity antenna system, reception is highly dependent on the antenna module receiving battery voltage from the radio. The antenna module has a built in antenna amplifier that boosts both AM and FM reception. The antenna module will switch between the internal and external antenna for best reception and provide feedback of this signal through the coax cable that connects the radio to the antenna module.

### Reference Information

#### Schematic Reference

Radio/Navigation System Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Radio/Audio 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

#### Antenna Circuit Testing w/o US3

1. Ignition OFF, disconnect the radio antenna coax cable from the radio and the radio antenna.
2. Test for infinite resistance between the antenna coax center terminal and ground.

⇒ | If less than the specified value, replace the antenna coax.

3. Test for less than 10 Ω on the antenna coax center terminal from end to end.

⇒ | If greater than the specified range, replace the antenna coax.

4. Test for less than 10 Ω on the antenna coax outer shield from end to end.

⇒ | If greater than the specified range, replace the antenna coax.

5. Test for infinite resistance between the coax center terminal and the outer shield.

⇒ | If less than the specified value, replace the antenna coax.

6. Reconnect the coax to the radio antenna. Test for infinite resistance on the coax at the radio between the center terminal and the outer shield.

⇒ | If less then specified value, replace the antenna.

7. Test for less than 10 Ω on the coax at the radio between the outer shield and ground.

⇒ | If greater than specified value, clean the mounting surface of the antenna ground plane. If no corrosion found, replace the antenna.

8. If all circuits test normal, replace the radio.

#### Antenna Circuit Testing w/US3

1. Ignition OFF, disconnect the radio antenna coax from the antenna module.
2. Ignition ON, radio tuned to FM, test for greater than 10 V between the coaxial center terminal and ground.

⇒ | If less than specified range, test the coax cable for a short to ground, or an open high resistance. If the cable test normal, replace the radio.

3. Radio tuned to AM, test for less than 1 V between the coaxial center terminal and ground.

⇒ | If greater than the specified range, test the coax for a short to voltage. If the cable test normal, replace the radio.

4. Inspect the radio antenna module grounding surfaces and the mounting hardware for any corrosion that may cause a poor ground.

⇒ | If corrosion is noted, clean the grounding surfaces or hardware.

5. Disconnect the X1 harness connector at the antenna module.
6. Ignition ON, radio ON, verify a test lamp illuminates between the entertainment remote enable signal circuit terminal 1, and ground.

⇒ | If test lamp does not illuminate, test the circuit for short to ground or an open/high resistance. If circuit tests normal, replace the radio.

7. If all circuits test normal, replace the antenna module.
8. Ignition ON, radio ON, verify radio reception has improved.

⇒ | If there is still poor reception, replace the radio.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Radio Antenna Module Replacement

• | Radio Antenna Base Replacement

• | Control Module References for radio replacement, setup, and programming