Pinpoint Test D: Poor Quality/Distorted/No Sound From All Speakers - THX(R) Audio System
Information and Entertainment System
Pinpoint Tests
Pinpoint Test D: Poor Quality/Distorted/No Sound From All Speakers - THX(R) Audio System
Refer to Wiring Diagram Set 130, Audio System/Navigation for schematic and connector information. Diagrams By Number
Normal Operation
When the key is in START, the Audio Control Module (ACM) receives voltage on the START signal circuit. The ACM then mutes the speaker output to prevent voltage spikes from producing a popping noise through the speakers. However, a short to voltage on this circuit causes the ACM output to be continuously muted.
If a speaker circuit fault DTC is set in the ACM, the cause of the concern is a short to ground or short to voltage in an individual speaker circuit, which has caused the ACM overload protection to activate. If a speaker circuit fault DTC is present, refer to DTC Charts. [1][2]Diagnostic Trouble Code Descriptions
To enable the audio Digital Signal Processing (DSP) module, the ACM sends voltage through the enable/clip circuit. The circuit acts as both an output (to enable the amplifier) and an input (to detect an amplifier overload condition). The voltage sent by the ACM passes through a variable resistor in the audio DSP module, then to ground. As the amplifier (integral to the audio DSP module) reaches maximum output, the resistance in the variable resistor decreases. This decreases the voltage drop, resulting in the ACM detecting a higher voltage on the enable/clip circuit. When the voltage reaches the clip threshold, the ACM clips the audio output signal to the audio DSP module (heard as distortion), in order to prevent damage to the amplifier and speakers.
The enable/clip status is based on the following voltages, as detected by the ACM:
- Less than 0.4 volt: amplifier disabled
- Between 3.8 and 6.7 volts: amplifier enabled
- Greater than 8.5 volts: amplifier clipped
This pinpoint test is intended to diagnose the following:
- Fuse
- Wiring, terminals or connectors
- Audio DSP module
- ACM
PINPOINT TEST D: POOR QUALITY/DISTORTED/NO SOUND FROM ALL SPEAKERS - THX(R) AUDIO SYSTEM
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
NOTE: Failure to disconnect the battery when instructed will result in false resistance readings. Refer to Battery.
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D1 CHECK THE START SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: ACM C240a.
- Measure the voltage between the ACM C240a-15, circuit CBP28 (GY/VT), harness side and ground.
- Is any voltage present?
Yes
REPAIR the circuit. TEST the system for normal operation.
No
GO to D2.
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D2 CHECK THE AUDIO DSP MODULE VOLTAGE SUPPLY
- Ignition OFF.
- Disconnect: Audio DSP Module C4348c.
- Measure the voltage between the audio DSP module, harness side and ground as follows:
- Are the voltages greater than 10 volts?
Yes
GO to D3.
No
VERIFY the Smart Junction Box (SJB) fuse 18 (20A) or fuse 28 (20A) is OK. If OK, REPAIR the circuit in question. TEST the system for normal operation. If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short.
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D3 CHECK THE AUDIO DSP MODULE GROUND CIRCUITS FOR CONTINUITY
- Disconnect: Negative Battery Cable.
- Measure the resistance between the audio DSP module, harness side and ground as follows:
- Are the resistances less than 5 ohms?
Yes
GO to D4.
No
REPAIR the circuit in question. TEST the system for normal operation.
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D4 CHECK THE AUDIO DSP MODULE ENABLE CIRCUIT FOR CORRECT VOLTAGE
- Connect: Negative Battery Cable.
- Connect: Audio DSP Module C4348c.
- Disconnect: Audio DSP Module C4348a.
- Operate the audio system in radio tuner (AM/FM) mode.
- Measure the voltage between the audio DSP module C4348a-3, circuit CME31 (BU/GN) (with navigation) or circuit SME23 (VT/RD) (without navigation), harness side and ground.
- Is the voltage between 3.8 and 6.7 volts?
Yes
GO to D8.
No
GO to D5.
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D5 CHECK THE AUDIO DSP MODULE ENABLE CIRCUIT FOR A SHORT TO VOLTAGE
- Disconnect: ACM C240a (With Navigation) or C240c (Without Navigation).
- Ignition ON.
- Measure the voltage between the audio DSP module C4348a-3, circuit CME31 (BU/GN) (with navigation) or circuit SME23 (VT/RD) (without navigation), harness side and ground.
- Is any voltage present?
Yes
REPAIR the circuit. TEST the system for normal operation.
No
GO to D6.
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D6 CHECK THE AUDIO DSP MODULE ENABLE CIRCUIT FOR AN OPEN OR SHORT TO GROUND
- Ignition OFF.
- For vehicles with navigation, measure the resistance between the audio DSP module C4348a-3, circuit CME31 (BU/GN), harness side and the ACM C240a-7, circuit CME31 (BU/GN), harness side; and between the audio DSP module C4348a-3, circuit CME31 (BU/GN), harness side and ground.
- For vehicles without navigation, measure the resistance between the audio DSP module C4348a-3, circuit SME23 (VT/RD), harness side and the ACM C240c-4, circuit SME23 (VT/RD), harness side; and between the audio DSP module C4348a-3, circuit SME23 (VT/RD), harness side and ground.
- Is the resistance less than 5 ohms between the audio DSP module and the ACM, and greater than 10,000 ohms between the audio DSP module and ground?
Yes
GO to D7.
No
REPAIR the circuit. TEST the system for normal operation.
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D7 CHECK FOR CORRECT ACM OPERATION
- Ignition OFF.
- Connect: All Disconnected Connectors.
- Disconnect all the ACM connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the ACM 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. REFER to Audio Control Module (ACM) 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.
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D8 CHECK FOR CORRECT AUDIO DSP MODULE OPERATION
- Ignition OFF.
- Connect: All Disconnected Connectors.
- Disconnect all the audio DSP module connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the audio DSP 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 audio DSP module. REFER to Audio Digital Signal Processing (DSP) Module Audio Digital Signal Processing (DSP) Module. 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.
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