U0252 Lost communication with lighting control module, rear B

OBD-II DTC Datasheet

Lost Communication With Lighting 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 Lighting Control Module B (LCMR-B) 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 rear lighting control module b is usually located behind the dashboard but can be found inside the trunk. It accepts input data from various 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 lighting in the rear of the vehicle. Refer to your specific vehicle handbook to determine which door is labeled “B” in your specific case.

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 always serious because of the safety issues that arise from the module not illuminating the rear of the vehicle.

Symptoms of a U0252 code may include:

No backlighting / partial backlighting
Dash / Message Center Indicator Light On

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 LCMR-B 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 U0252 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 U0252, try accessing the back b of the lighting control module (LCMR-B). If you can access codes from LCMR-B then code U0252 is either intermittent or memory code. If the LCMR-B cannot be accessed, then code U0252 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 back of the lighting control module. b.

Check all fuses supplying the LCMR-B module on this vehicle. Check all grounds for LCMR-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 memory and see if U0252 returns or you can contact the LCMR-B module. If no code is returned or communication is restored, the problem is most likely a fuse / connection issue.

If the code returns, locate the CAN bus communication connections on your vehicle, most importantly the LCMR-B connector, which is usually located behind the dashboard but can be found inside the trunk. Disconnect the negative battery cable before disconnecting the connector on the LCMR-B module. 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 LCMR-B. You will need access to a digital volt-ohmmeter (DVOM). Make sure the LCMR-B has power and ground. Access the wiring diagram and determine where the primary power and ground supplies enter the LCMR-B. Reconnect the battery before proceeding with the LCMR-B still disconnected. Connect the red wire of your voltmeter to each B + (battery voltage) power source going to the LCMR-B connector, and the black wire of your voltmeter to a good ground (if unsure, the negative pole of the battery always works). You should see the battery voltage reading. Make sure you have a good reason. Connect the red wire from the voltmeter to battery positive (B +) and the black wire 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 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 if you were unable to reset DTC U0252, the only thing you can do is seek help from a trained automotive diagnostician, as this will indicate a failed LCMR-B. . Most of these LCMR-Bs must be programmed or calibrated in order to properly mount the vehicle.

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