For 1990-2009 cars

Schematic Reference: Radio/Audio System Schematics

### Diagnostic System Check - Vehicle

Always perform the Diagnostic System Check - Vehicle, before proceeding with these diagnostic procedures. Refer to Diagnostic System Check - Vehicle .

### Diversity Antenna System

This diversity antenna system is comprised of 3 antenna grid patterns interfacing with the rear defog grid, a radio antenna module, a coax, and a 14-volt power feed from the radio to the antenna module.

In AM and WX mode, the system functions as follows:

The antenna module takes the signal from only the AM/FM1 antenna pattern on the rear window. The antenna module amplifies this signal and sends it to the radio. In this mode the radio does not supply any voltage to the center conductor of the coax and there is no feedback signal present on the coax.

In FM mode, the system functions as follows:

The antenna module takes the best signal from one of the three (3) FM antenna patterns on the rear window. The antenna module amplifies this signal and sends it to the radio. In this mode the radio supplies 12V to the center conductor of the coax and this switches the module into FM mode. The radio also supplies a feedback signal, along the coax, to the AM/FM antenna module, which indicates the quality of the signal. Based on the measured input signal level and the feedback from the radio, the antenna module switches between the 3 antennas to find the best signal.

The following information lists the most probable cause of the concern to the least probable cause, followed by the appropriate test for that condition. If the list leads to the replacement of a component, always inspect for a poor connection before proceeding with the replacement. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Perform the Antenna System Test and test the antenna coax cable prior to performing any of the following tests.

#### Poor Reception on Both AM and FM Bands

• | The radio antenna module is not grounded properly. The module grounding screws should be clean and tight. The antenna module ground is either a chassis ground or a ground strap. Measure the resistance from the antenna module base plate to a good ground. The resistance measured should be 0.2 ohms or less. Find and correct the condition if the resistance is out of specification.

• | The antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .

• | Defective Antenna Module-Replace the antenna module, Refer to Radio Antenna Module Replacement for service procedures.

• | Defective antenna grid--Refer to Rear Window Replacement .

#### Poor Reception on AM Band Only

• | The antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .

• | Defective antenna module--Replace the antenna module. Refer to Radio Antenna Module Replacement for service procedure.

• | Defective antenna grid--Refer to Rear Window Replacement .

#### Poor Reception on FM Band Only

• | The Antenna 14-volt switch supply voltage circuit to the radio antenna module is open or shorted to ground. Test the antenna 14-volt switch supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .

• | Defective antenna module--Replace the antenna module. Refer to Radio Antenna Module Replacement for service procedure.

• | Defective antenna grid--Refer to Rear Window Replacement .