Diagnostic Routine A
Diagnostic Routine A
Diagnostic Overview
Poor Reception - AM-FM
Refer to Wiring Diagram Set 130 for schematic and connector information Electrical Diagrams.
Normal Operation and Fault Conditions
REFER to AM - FM Radio .
The RDS (Radio Data System) function allows the vehicle operator to choose which genre (category) of music to listen to. When the SCAN button is pressed, the ACM (Audio Control Module) only stops at channels falling within the selected category. If no channel in the selected category is found, the ACM (Audio Control Module) continues to scan without stopping. This may appear to be a reception issue, but it is actually due to the customer setting.
DTC Fault Trigger Conditions
Pinpoint Test
1. CHECK THE AUDIO SYSTEM RECEPTION
1. Operate the audio system in radio tuner (AM/FM (Amplitude Modulation/Frequency Modulation)) mode.
2. Check the reception with the engine running, and with the engine off.
Does the poor reception only occur with the engine running?
2. CHECK THE GENERATOR
NOTE: If the engine is operated at greater than 2,000 RPM (Revolutions Per Minute) momentarily, the generator self-excites. Make sure when the generator is disconnected the engine rpm stays below 2,000 RPM (Revolutions Per Minute). If it does rise above 2,000 RPM (Revolutions Per Minute), turn the ignition to the OFF position and start the test over again.
1. Ignition OFF.
2. Disconnect the wiring harness from the generator voltage regulator.
3. Start the engine.
4. Operate the audio system in radio tuner (AM/FM (Amplitude Modulation/Frequency Modulation)) mode.
Is the reception OK?
3. CHECK THE IGNITION CIRCUITS
1. Ignition OFF.
2. Connect the wiring harness to the voltage regulator.
3. Visually inspect the engine compartment and make sure all ignition coils are correctly and securely connected, and that there are no visible cracks in the coil housings.
4. Inspect all the wiring harnesses and connectors for damaged insulation and loose or broken conditions.
Are the ignition components OK?
4. CHECK THE ANTENNA ENABLE CIRCUIT
1. Ignition OFF.
2. Disconnect: Antenna.
3. Ignition ON.
4. Operate the audio system in radio tuner (AM/FM (Amplitude Modulation/Frequency Modulation)) mode.
5. Measure:
Is the voltage greater than 11 volts?
5. CHECK THE ANTENNA ENABLE CIRCUIT FOR AN OPEN
1. Ignition OFF.
2. Disconnect: ACM (Audio Control Module) C240A.
3. Measure:
Is the resistance less than 3 ohms?
6. CHECK THE ANTENNA ENABLE CIRCUIT FOR A SHORT TO GROUND
1. Measure:
Is the resistance greater than 10,000 ohms?
7. CHECK THE AM/FM ANTENNA CABLE
1. Ignition OFF.
2. Disconnect: AM/FM (Amplitude Modulation/Frequency Modulation) Antenna In-Line Connection At RH (Right Hand) Scuff Plate Trim Panel.
3. Disconnect: AM/FM (Amplitude Modulation/Frequency Modulation) Antenna Cable At ACM (Audio Control Module).
4. Measure the resistance of the rear ACM (Audio Control Module) antenna cable core between the antenna and the front ACM (Audio Control Module) antenna cable in-line connection; and between the rear ACM (Audio Control Module) antenna cable core and shield.
5. Measure the resistance of the front ACM (Audio Control Module) antenna cable core between the ACM (Audio Control Module) and the rear ACM (Audio Control Module) antenna cable in-line connection; and between the front AM/FM (Amplitude Modulation/Frequency Modulation) antenna cable core and shield.
Is the resistance of each AM/FM (Amplitude Modulation/Frequency Modulation) antenna cable core less than 2 ohms, and the resistance between the core and shield of each ACM (Audio Control Module) antenna cable greater than 10,000 ohms?
8. ISOLATE THE ANTENNA
1. Connect: AM/FM (Amplitude Modulation/Frequency Modulation) Antenna In-Line Connection At RH (Right Hand) Scuff Plate Trim Panel.
2. Connect: AM/FM (Amplitude Modulation/Frequency Modulation) Antenna Cable At ACM (Audio Control Module).
3. Install a new antenna. REFER to Antenna .
4. Operate the audio system in radio tuner (AM/FM (Amplitude Modulation/Frequency Modulation)) mode.
Is the reception OK?
9. ISOLATE THE ANTENNA CABLE
1. Ignition OFF.
2. Substitute each antenna cable by routing a new component. Do not remove the original antenna cable at this time.
3. Operate the audio system in radio tuner (AM/FM (Amplitude Modulation/Frequency Modulation)) mode.
Is the reception OK?
10. CHECK FOR CORRECT ACM (Audio Control Module) OPERATION
1. Ignition OFF.
2. Disconnect and inspect all ACM (Audio Control Module) connectors.
3. Repair:
- corrosion (install new connectors or terminals - clean module pins)
- damaged or bent pins - install new terminals pins
- pushed-out pins - install new pins as necessary
4. Reconnect the ACM (Audio Control Module) connectors. Make sure they seat and latch correctly.
5. Operate the system and determine if the concern is still present.
Is the concern still present?
