Poor Radio Reception

Poor Radio Reception

Fault symptoms
Poor radio reception.
The cassette player and CD player work normally.

Probable Cause Of Fault
- Main unit not properly inserted in radio compartment.
- Poor connection of aerial cable to radio compartment.
- Poor coaxial cable connection.
- Aerial amplifier's power supply (trigger voltage) or ground connection faulty.
- Break in glass aerial (rear window).
- Poor connection between aerial amplifier and glass aerial.

Diagnostic Help
Note that the glass-mounted mobile phone aerial on the rear window can cause a deterioration in radio reception.

Check Wiring Harness
Jiggle the wiring harness at several points and in different directions to reveal intermittent breaks and short-circuits in the leads. Observe the multimeter, test lamp or diagnostic instrument during the test.





Diagnostic Procedure

1 Checking the mounting of the main unit in the radio compartment
- Check that the main unit is correctly inserted (fitted) in the radio compartment.

Test Results OK?
YES
Continue with point 2.
NO
Repair or replace, and continue with point 6, Final Check.






2 Checking the Aerial Amplifier's Power Supply
(trigger voltage) and ground connection
- Undo the aerial amplifier's 1-pole connector (trigger voltage).
- Turn the ignition switch to ON.
- Switch on the audio system.
- Connect a test lamp to:
- the pin of the 1-pole connector and a good grounding point.
The test lamp should light
- Remove the aerial amplifier and clean both ground connections on the amplifier and the area around the studs and screw hole in the body.
- Refit the aerial amplifier.
- The aerial amplifier should be properly grounded at both studs.

Test Results OK?
YES
- If the trouble occurs on both FM and AM reception, continue with point 3.
- If the trouble occurs on FM reception only, continue with point 3.
- If the trouble occurs on AM reception only, continue with point 5.
NO
Repair or replace the lead concerned and continue with point 6, Final Check.






3 Checking the Glass Aerial
- Undo the 1-pole connector between the aerial amplifier and the rear window.
- Undo the aerial filter's connection to the electrically heated rear window.
- Take a resistance reading across:
- the connection on the rear window for FM1 and the aerial connection to the aerial filter.
The resistance should be < 1 ohm.
- Take a resistance reading across:
- The connection on the electrically heated rear window for the aerial filter and ground.
The resistance should be infinite.
(Aerial system 2 only:)
- Unplug the 2-pin connector between the aerial amplifier and the electrically heated rear window.
- Take a resistance reading across:
- the connection on the rear window for FM2 and the aerial connection to the aerial filter
The resistance should be 5-10 ohms.
Reconnect the two 1-pole connectors and the 2-pin connector

Test Results OK?
YES
Continue with point 4.
NO
Rectify and replace the electrically heated rear window if necessary.






4 Checking the Aerial Cable
- Remove the main unit.
- Check that the aerial cable is correctly attached to the console.
- Undo the aerial cable's connection to the aerial amplifier.
- Take a resistance reading across:
- the braiding of the coaxial cable and a good grounding point.
The resistance should be infinite.
- Take a resistance reading across:
- the centre conductor of the coaxial cable and a good grounding point.
The resistance should be infinite.
- Connect a jumper lead between the centre conductor and the braiding at the aerial amplifier.
- Take a resistance reading across:
- the centre conductor and the cable braiding at the main unit.
The resistance should be less than 2 ohms.

Test Results OK?
YES
Replace the aerial amplifier.
Continue with point 6, Final Check.
NO
Replace the aerial cable.
Continue with point 6, Final Check.






5 Checking the AM Aerial
- Check that the 2-pin connector is securely attached to the rear window.
- Check visually through the rear window that the AM loop is fault-free.
- Unplug the 2-pin connector.
- Take a resistance reading across:
- the AM connection and a good grounding point.
The resistance should be infinite.

Test Results OK?
YES
Replace the aerial amplifier.
Continue with point 6, Final Check.
NO
Repair or replace the connector or electrically heated rear window.
Continue with point 6, Final Check.






6 Final Check
- Carry out a function check.
- Evaluate the function check.
- Check that the symptom has not recurred.

Has the Symptom Recurred?
YES
Continue with Fault diagnosis, general, "Before changing a control module." Before Changing A Control Module
NO
The steps taken to rectify the fault were correct.