U0181 Lost Communication With Dynamic Headlight Range Control Module
OBD2 Error Codes

U0181 Lost Communication With Dynamic Headlight Range Control Module

U0181 Lost Communication With Dynamic Headlight Range Control Module

OBD-II DTC Datasheet

Lost Communication With Dynamic Headlight Range Control Module

What does this mean?

This is a generic communications DTC that applies to most car brands and models, but is most commonly used by Buick, Cadillac, Chevrolet, GMC, Pontiac, and Saturn.

This code means that the dynamic headlamp leveling control module (DHLCM) 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 dynamic headlight range control module is usually located inside the engine compartment behind the headlights. It receives input data from various sensors, some of which are directly connected to it, most of which are transmitted via a bus communication system. These inputs allow the module to control the direction of the headlights regardless of the vehicle level.

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 will not be an issue due to the module's backup capabilities. If an electrical problem occurs, the module has a backup module and will default to neutral like any other vehicle.

Symptoms of a U0181 code may include:

  • Headlights do not adjust automatically / do not align

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 DHLCM
  • 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 U0181 code before any of the major codes are thoroughly diagnosed and rejected.

If your scan tool can access fault codes and the only code you are getting from other modules is U0181, try accessing the Dynamic Headlamp Leveling Control Module (DHLCM). If you can access codes from the DHLCM, then the U0181 code is either intermittent or a memory code. If you cannot access the DHLCM, then the U0181 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 dynamic headlamp leveling control module.

Check all fuses supplying the DHLCM on this vehicle. Check all grounds for DHLCM. 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 DTCs from memory and see if U0181 returns or you can contact the DHLCM. 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 connections on your vehicle, especially the DHLCM connector, which is usually found inside the engine compartment behind the headlights. Disconnect the negative battery cable before disconnecting the connector on the DHLCM. Once found, 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 connecting the connectors back to the DHLCM, 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 DHLCM. Access the wiring diagram and determine where the main power and ground connections enter the DHLCM. Connect the battery before continuing, with the DHLCM still disconnected. Connect the red lead of your volt meter to each B+ power source (battery voltage) entering the DHLCM 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+) battery terminal, and the black lead to each ground circuit. Once again, you should see battery voltage with each connection. If not, troubleshoot the power or ground circuit.

Next, check the two communication circuits. Find CAN B+ (or MSCAN+ circuit) and CAN B- (or MSCAN – circuit). With the black lead of the voltmeter connected to a good ground, connect the red lead to CAN B+. With the key on and the engine off, you should see about 0.5 volts with slight fluctuations. Then connect the red lead of the 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 are unable to reset the U0181 trouble code, the only thing to do is to seek help from a trained automotive diagnostician, as this would indicate a DHLCM failure. Most of these DHLCMs need to be programmed or calibrated to properly install the vehicle.

Related DTC discussions

  • There are currently no related topics in our forums. Post a new topic on the forum now.

Need more help with the U0181 code?

If you still need help with DTC U0181, post a question in the comments below this article.

NOTE. This information is provided for informational purposes only. It is not intended to be used as a repair recommendation and we are not responsible for any action you take on any vehicle. All information on this site is protected by copyright.

Add a comment