U0186 Lost communication with audio amplifier A

OBD-II DTC Datasheet

Lost Communication with Audio Amplifier A

What does this mean?

This is a generic communications system diagnostic trouble code that applies to most makes and models of OBD-II vehicles.

This code means that the audio amplifier A (AACM-A) and other control modules on the vehicle do not communicate with each other. The circuitry most commonly used for communication is known as Controller Area Bus communication, or simply the CAN bus.

Without this CAN bus, control modules cannot communicate and your scan tool may not receive information from the vehicle, depending on which circuit is involved.

The audio amplifier a is usually located behind the dashboard, usually in the center of the dashboard closest to the radio, although in some cases it can be found in the trunk. It accepts input from a variety of sensors, some of which are directly connected to it, and most are transmitted over a bus communication system. These inputs allow the module to control the operation of the antenna (if it is motorized, raise and lower; if used for multiple frequency bands or operations, switch to different operations - AM / FM / Satellite / Navigation).

Troubleshooting steps may vary depending on the manufacturer, the type of communication system, the number of wires, and the colors of the wires in the communication system.

Code severity and symptoms

The severity in this case is never serious, as this is a device for the convenience of customers. Lack of operation of the AACM-A does not in any way affect the operation of the vehicle.

Symptoms of a U0186 code may include:

Radio does not transmit information / no sound / possibly blank screen
AACM-A does not turn on / does not work

reasons

Usually the reason for installing this code is:

Open on CAN bus + or - circuit
Short to ground or ground in any CAN bus circuit
No power or ground to the AACM-A module
Rarely - the control module is faulty

Diagnostic and repair procedures

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

First, look for other DTCs. If any of these are bus communication or battery / ignition related, diagnose them first. Misdiagnosis is known to occur if you diagnose the U0186 code before any of the major codes are thoroughly diagnosed and rejected.

If your scan tool can access trouble codes and the only code you are getting from other modules is U0186, try accessing Audio Amplifier A (AACM-A). If you can access codes from AACM-A then code U0186 is either intermittent or memory code. If AACM-A cannot be accessed, then code U0186 set by other modules is active and the problem already exists.

The most common failure is a circuit failure that results in loss of power or ground to the audio amplifier a.

Check all fuses supplying the AACM-A on this vehicle. Check all the grounds for AACM-A. Locate grounding attachment points on the vehicle and make sure these connections are clean and secure. If necessary, remove them, take a small wire bristle brush and baking soda / water solution and clean each one, both the connector and the place where it connects.

If any repairs have been made, clear the DTCs from memory and see if U0186 returns or you can contact the AACM-A module. If no code is returned or communication is restored, the problem is most likely a fuse / connection issue.

If the code returns, look for the CAN bus communication connections on your vehicle, most importantly the AACM-A connector, which is usually located behind the dashboard, usually in the center of the dashboard closest to the radio, although in some applications it can be found in the trunk. Disconnect the negative battery cable before disconnecting the connector on the AACM-A. Once detected, visually inspect the connectors and wiring. Look for scratches, scuffs, exposed wires, burn marks, or molten plastic.

Disconnect the connectors and carefully inspect the terminals (metal parts) inside the connectors. See if they look burnt or have a green tint indicating corrosion. If you need to clean the terminals, use an electrical contact cleaner and a plastic bristle brush. Allow to dry and apply electrical grease where the terminals touch.

Perform these few voltage checks before reconnecting the connectors to the AACM-A. You will need access to a digital volt/ohmmeter (DVOM). Make sure you have power and ground on AACM-A. Access the wiring diagram and determine where the main power and ground supplies enter the AACM-A. Connect the battery before continuing with the AACM-A still disconnected. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply included in the AACM-A connector, and the black lead of your voltmeter to a good ground (if unsure, battery negative always works). You should see the battery voltage reading. Make sure you have a good reason. Connect the red lead of the voltmeter to the battery positive (B+) and the black lead to each ground circuit. Once again, you should see the battery voltage every time you connect. If not, repair the power or ground circuit.

Then check the two communication circuits. Locate CAN B+ (or MSCAN + circuit) and CAN B- (or MSCAN - circuit). With the black wire of the voltmeter connected to a good ground, connect the red wire to CAN B+. With the key on and the engine off, you should see a voltage of about 0.5 volts with little fluctuation. Then connect the red lead of a voltmeter to the CAN B circuit. You should see about 4.4 volts with slight fluctuations.

If all tests pass and communication is still not possible, or you were unable to clear DTC U0186, the only thing that can be done is to seek help from a trained automotive diagnostician, as this will indicate an AACM-A failure. . Most of these AACM-A's must be programmed or calibrated in order to properly install the vehicle.

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