U0135 Lost communication with front differential control module

OBD-II DTC Datasheet

Lost Communication With Front Differential Control Module

What does this mean?

This is a generic communication system diagnostic trouble code that applies to most makes and models of vehicles.

This code means that the front differential control module (DCM) 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.

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 FDCM receives input data from various sensors, some of which are directly connected to it and some of which are transmitted over a bus communication system. These inputs allow the module to control the drivetrain application, typically when it is in an all-wheel drive application. It also has the ability to lock axles with differential, 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.

Severity and symptoms

The severity in this case depends on the system. Because this transmission system provides safety during violent acceleration / cornering maneuvers, safety is a concern when diagnosing these systems. In addition, safety is important when servicing these systems. ALWAYS refer to the service information before disassembling / diagnosing these systems.

Symptoms of a U0135 engine code may include:

Fault indicator light is on
Traction control light on or flashing - depending on system

reasons

Usually the reason for installing this code is:

Open in CAN + bus circuit
Open in the CAN bus - electrical circuit
Short circuit to power in any CAN bus circuit
Short to ground in any CAN bus circuit
Loss of power or ground to the DCM - most common
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.

If your scan tool can access trouble codes and the only code you are pulling from other modules is U0135, try accessing the front differential control module. If you can access the codes from the DCM, then code U0135 is either an intermittent or memory code. If you cannot access the codes for the DCM module, then code U0135 set by other modules is active and the problem already exists.

The most common failure is a loss of power or ground to the DCM.

Check all fuses supplying the DCM on this vehicle. Check all the reasons for DCM. 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 U0135 returns or you can contact the DCM. 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 C bus connections on your specific vehicle, especially the DCM connector. Disconnect the negative battery cable before disconnecting the connector on the DCM. 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 plugging the connectors back into the DCM. You will need access to a digital volt-ohmmeter (DVOM). Make sure the DCM has power and ground. Access the wiring diagram and determine where the primary power and ground supplies go into the DCM. Reconnect the battery before proceeding with the DCM still disconnected. Connect the red wire of your voltmeter to each B + (battery voltage) power source going into the DCM connector, and the black wire of your voltmeter to a good ground (if unsure, the negative pole of the battery always works). You can see the battery voltage reading. Make sure you have a good reason. Connect the red lead from the voltmeter to battery positive (B +) and the black lead to each ground. Once again, you should see the battery voltage every time you plug it in. If not, troubleshoot 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 U0135, the only thing you can do is seek help from a trained automotive diagnostician, as this will indicate a faulty DCM. Most of these DCMs must be programmed or calibrated for the vehicle in order to be properly installed.

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