U011D Lost Communication With Four-Wheel Drive Control Module

U011D Lost Communication With Four-Wheel Drive Control Module

OBD-II DTC Datasheet

Lost Communication With Four-Wheel Drive Control Module

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 four-wheel drive control module (AWDCM) 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 four-wheel drive control module (AWDCM) is usually located behind the dashboard, usually next to the drive switch. It can also be located under the passenger compartment, near the transfer case. May also be part of PCM. It receives input from a variety of sensors, some of which are directly connected to it, and most are sent over a bus communication system from the powertrain control module (PCM). These inputs allow the module to be controlled as a powertrain application, perhaps whether it is a two or four wheel drive application. It can also change the gear ratio applied to the drive axles and the amount of torque applied to the transmission.

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 not serious because PCM has a backup strategy in case it loses communication with AWDCM.

Symptoms of a U011D code may include:

• The traction control indicator light is on or flashing, depending on the system
• Check if the suspension light is on, depending on the system.

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 AWDCM
• 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 U011D code before any of the underlying codes are thoroughly diagnosed and corrected.

If the only code you get from other modules is U011D, try accessing AWDCM. If you can access codes from AWDCM then code U011D is either intermittent or memory code. If AWDCM cannot be accessed, then code U011D set by other modules is active and the problem already exists.

The most common failure is a circuit failure that results in a loss of power or ground to the AWD control module.

Check all fuses supplying the AWDCM on this vehicle. Check out all the reasons for AWDCM. Locate ground anchorage 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 diagnostic trouble codes from any modules that set the code in memory and see if you can now communicate with the AWDCM module. If communication with the AWDCM recovers, the problem is most likely a fuse / connection issue.

If the code returns or communication with the module still cannot be established, locate the CAN bus communication connections on your vehicle, most importantly the AWDCM connector, which is usually located behind the dashboard, usually near the drive switch. It can also be located under the passenger compartment, next to the transfer case. can also be part of the RMB. Disconnect the negative battery cable before disconnecting the connector on the AWDCM. 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 connecting the connectors back to the AWDCM. You will need access to a digital volt/ohmmeter (DVOM). Make sure the AWDCM has power and ground. Access the wiring diagram and determine where the main power and ground sources enter the AWDCM. Reconnect the battery before proceeding with AWDCM still disabled. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply going into the AWDCM connector, and the black lead of your voltmeter to a good ground (if you're 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 C+ (or HSCAN+) and CAN C- (or HSCAN - circuit). With the black wire of the voltmeter connected to a good ground, connect the red wire to CAN C+. With the key on and engine off, you should see about 2.6 volts with little fluctuation. Then connect the red wire of the voltmeter to the CAN C- circuit. You should see about 2.4 volts with little fluctuation. Other manufacturers show CAN C- at about 5V and an oscillating key with the engine off. Check your manufacturer's specifications.

If all tests pass and communication is still not possible, or you were unable to reset DTC U011D, the only thing that can be done is to seek help from a trained automotive diagnostician, as this will indicate an AWDCM failure. Most of these AWDCMs must be programmed or calibrated in order to properly install the vehicle.

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