Pinpoint Test D: Poor Quality/Distorted/No Sound From All Speakers
Information and Entertainment System
Pinpoint Tests
Pinpoint Test D: Poor Quality/Distorted/No Sound From All Speakers
Refer to Wiring Diagram Set 130, Audio System/Navigation for schematic and connector information. Diagrams By Number
Normal Operation
When the ignition is in the START position, voltage is supplied to the Audio Control Module (ACM) through the START sense circuit. When the ACM receives this voltage, it mutes the speaker output to prevent popping in the speakers as a result of voltage spikes during engine cranking. However, if there is a short to voltage on this circuit, the ACM continually mutes the audio output, resulting in no sound from all speakers.
For vehicles with navigation, the ACM sends voltage to the audio amplifier through the enable/clip circuit in order to enable the audio amplifier. 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 amplifier, then to ground. As the audio amplifier 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 amplifier (heard as distortion), in order to prevent damage to the amplifier and speakers.
The clip/enable 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
An open in the enable/clip circuit causes the speakers to produce no sound, because the enable signal does not reach the audio amplifier. A short to ground or short to voltage can cause severe distortion to be heard in the speakers.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Audio amplifier (vehicles with navigation)
- ACM
PINPOINT TEST D: POOR QUALITY/DISTORTED/NO SOUND FROM ALL SPEAKERS
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 SENSE CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: ACM C240a.
- Ignition ON.
- 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
If the vehicle is equipped with navigation, GO to D2.
Otherwise, GO to D7.
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D2 CHECK THE AUDIO AMPLIFIER VOLTAGE
- Ignition OFF.
- Disconnect: Audio Amplifier C2385b.
- Measure the voltage between the audio amplifier C2385b-1, circuit SBP03 (BU/RD), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to D3.
No
VERIFY the Smart Junction Box (SJB) fuse 3 (15A) 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.
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D3 CHECK THE AUDIO AMPLIFIER GROUND CIRCUIT FOR CONTINUITY
- Disconnect: Negative Battery Cable.
- Measure the resistance between the audio amplifier C2385b-7, circuit GD115 (BK/GY), harness side and ground; and between the audio amplifier C2385b-14, circuit GD115 (BK/GY), harness side and ground.
- 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 AMPLIFIER ENABLE CIRCUIT VOLTAGE
- Operate the audio system in radio tuner (AM/FM) mode.
- Measure the voltage between the audio amplifier C2385b-9, circuit CME27 (YE/VT), harness side and ground.
- Is the voltage between 3.8 and 6.7 volts?
Yes
INSTALL a new audio amplifier. REFER to Audio Amplifier Service and Repair. TEST the system for normal operation.
No
GO to D5.
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D5 CHECK THE AUDIO AMPLIFIER ENABLE CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: ACM C240a.
- Ignition ON.
- Measure the voltage between the audio amplifier C2385b-9, circuit CME27 (YE/VT), 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 AMPLIFIER ENABLE CIRCUIT FOR AN OPEN OR SHORT TO GROUND
- Ignition OFF.
- Measure the resistance between the audio amplifier C2385b-9, circuit CME27 (YE/VT), harness side and the ACM C240a-7, circuit CME27 (YE/VT), harness side; and between the audio amplifier C2385b-9, circuit CME27 (YE/VT), harness side and ground.
- Is the resistance less than 5 ohms between the audio amplifier and the ACM, and greater than 10,000 ohms between the audio amplifier 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: Audio Amplifier C2385b.
- Disconnect all the ACM connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect 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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