U0249 Lost Communication With Infotainment Control Module, Rear B

U0249 Lost Communication With Infotainment Control Module, Rear B

OBD-II DTC Datasheet

Lost Communication With Entertainment Control Module Rear B

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 the rear B of the infotainment control module (ECMR-B) and other control modules on the vehicle are not communicating with each other. The circuitry most commonly used for communication is known as Controller Area Bus communication, or simply the CAN bus.

Modules communicate with each other over a network, just like the network you have at home or work. Car manufacturers use several networked systems. Prior to 2004, the most common (non-exhaustive) inter-module communication systems were the serial communication interface, or SCI; SAE J1850 or PCI bus; and Chrysler Collision Detection, or CCD. The most common system used after 2004 is known as Controller Area Network communication, or simply the CAN bus (also used until 2004 on a small segment of vehicles). Without this CAN bus, control modules cannot communicate and your scan tool may or may not receive information from the vehicle, depending on which circuit is affected.

The rear entertainment control unit B (ECMR-B) is usually located behind the dashboard or center console, usually in the center of the vehicle. It receives input from a variety of sensors, some of which are directly connected to it, and most are transmitted over a bus communication system from the powertrain control module (PCM). It interacts with the radio, and in some cases replaces the radio. These inputs allow the module to control the information displayed and played back through the ECMR-B.

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 ECMR-B unit does not in any way affect the operation of the vehicle.

Symptoms of a U0249 code may include:

• ECMR-B gives no information / no sound / possibly blank screen
• ECMR-B does not turn on / does not work

reasons

Usually the reason for installing this code is:

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

Diagnostic and repair procedures

A good place to start with ALL electrical diagnostics is to check the Technical Service Bulletins (TSB) for your vehicle. The problem you are facing may be known to others in the field. A known fix may have been released by the manufacturer and can save you time and money during diagnostics.

It is assumed that you have access to a code reader at this point, as you may have been able to access the codes up until now. See if there were any other DTCs related to bus communication or battery / ignition. If so, you should diagnose them first, as misdiagnosis is known to occur if you diagnose the U0249 code before any of the underlying codes are thoroughly diagnosed and corrected.

If the only code you get from other modules is U0249, try accessing ECMR-B. If you can access codes from ECMR-B, then the U0249 code is either intermittent or a memory code. If you cannot access ECMR-B, then the U0249 code set by other modules is active and the problem already exists.

The most common fault is a circuit fault that results in a loss of power or ground to the rear of the entertainment control module. B.

Check all fuses supplying the ECMR-B module on this vehicle. Check all the grounds for ECMR-B. 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 any modules that set the code in memory and see if you can now communicate with the ECMR-B module. If communication with the ECMR-B recovers, the problem is most likely a fuse / connection issue.

If the code returns or communication still cannot be established with the module, locate the CAN bus communication connections on your vehicle, most importantly the ECMR-B connector, which is usually located behind the dashboard or on the center console, usually in the center of the vehicle. Disconnect the negative battery cable before disconnecting the connector from the ECMR-B. 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.

Before reconnecting the connectors to the ECMR-B, perform these few voltage checks. You will need access to a digital volt ohm meter (DVOM). Make sure there is power and ground at the ECMR-B. Access the wiring diagram and determine where the main power and ground sources enter the ECMR-B. Reconnect the battery before continuing, with the ECMR-B still disconnected. Connect the red lead of your volt meter to each B+ (battery voltage) source entering the ECMR-B connector, and the black lead of your volt meter to a good ground (if unsure, the negative post of the battery always works). You should see a battery voltage reading. Make sure you have a good ground. Connect the red lead of your volt meter to the positive (B+) terminal of the battery, and the black lead to each ground circuit. Once again, you should see battery voltage at each connection. If not, troubleshoot the power or ground circuit.

Next, check the two communication circuits. Find the CAN C+ (or HSCAN+) circuit and the CAN C- (or HSCAN – circuit). With the black lead of the voltmeter connected to a good ground, connect the red lead to CAN C+. With the key on and the engine off, you should see about 2.6 volts with a little oscillation. Then connect the red lead of the voltmeter to the CAN C- circuit. You should see about 2.4 volts with a little oscillation. Other manufacturers show CAN C- at about 5 volts and a oscillating key with the engine off. Check your manufacturer's specifications.

If all tests pass and communication is still not possible, or you have failed to reset the U0249 trouble code, the only thing to do is to seek help from a trained automotive diagnostician, as this will indicate a faulty ECMR-B. Most of these ECMR-Bs need to be programmed or calibrated to properly fit the vehicle.

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