Pinpoint Test R: Loud Popping Sound When Cycling The Ignition Switch

Information and Entertainment System

Pinpoint Test R: Loud Popping Sound When Cycling The Ignition Switch

Refer to Wiring Diagram Set 130, Audio System/Navigation for schematic and connector information [1][2]Diagrams By Number.

Normal Operation

Voltage is sent through the start input circuit to the Audio Front Control Module (ACM) with the ignition in the START position. Upon receiving this signal, the ACM (Audio Front Control Module) mutes all speaker outputs to eliminate the possibility of voltage spikes producing a popping noise through the speakers.

The ACM (Audio Front Control Module) disables the audio amplifier and subwoofer amplifier while the ignition is in the START position by keeping the enable circuit voltages below 0.4 volt.

If there is a short to voltage on any of the enable circuits, distortion is heard in the speakers whenever the ACM (Audio Front Control Module) is powered up, and that should be the primary concern addressed. If the speakers have distorted sound, GO to Symptom Chart - Sound Quality Symptom Chart - Sound Quality.

This pinpoint test is intended to diagnose the following:

- Fuse

- Wiring, terminals or connectors

- ACM (Audio Front Control Module)

PINPOINT TEST R : LOUD POPPING SOUND WHEN CYCLING THE IGNITION SWITCH

NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

R1 CHECK THE START INPUT CIRCUIT VOLTAGE

- Ignition OFF.

- Disconnect: ACM (Audio Front Control Module) C290D.

- Disconnect: Starter Relay.

- Hold the key in the START position.

- Measure the voltage between the ACM (Audio Front Control Module) C290D-15, circuit CBP28 (GY/VT), harness side and ground.





Is the voltage greater than 10 volts?

Yes
GO to R2.

No
VERIFY the Smart Junction Box (SJB) fuse 28 (5A) is OK. If OK, REPAIR the circuit. TEST the system for normal operation. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short [1][2]Diagrams By Number.

R2 ISOLATE THE FRONT/REAR SUBWOOFERS

NOTE: Repeat this step for each subwoofer amplifier.

- Ignition OFF.

- Connect: ACM (Audio Front Control Module) C290D.

- Disconnect: Suspect Subwoofer Amplifier.

- Cycle the key through all of the ignition switch positions.

Is a loud popping sound present for only one subwoofer amplifier?

Yes
INSTALL a new subwoofer amplifier for the suspect subwoofer amplifier. REFER to Subwoofer Amplifier - Door or Subwoofer Amplifier - Luggage Compartment . TEST the system for normal operation.

No
GO to R3.

R3 CHECK FOR CORRECT ACM (Audio Front Control Module) OPERATION

- Connect: Starter Relay.

- Disconnect all the ACM (Audio Front Control Module) connectors.

- Check for:
- corrosion

- damaged pins

- pushed-out pins


- Connect all the ACM (Audio Front Control Module) connectors and make sure they seat correctly.

- Operate the system and determine if the concern is still present.

Is the concern still present?

Yes
INSTALL a new ACM (Audio Front Control Module). REFER to Audio Control Module (ACM) . TEST the system for normal operation.

No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.