U0241 Lost Communication With Headlamp Control Module A
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U0241 Lost Communication With Headlamp Control Module A
OBD-II DTC Datasheet
Lost Communication With Headlamp Control Module A
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 Headlight Control Module A (HCM-A) 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.
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 Headlamp Control Module A (HCM-A) is usually located behind the dashboard next to the headlamp switch. Can also be installed under the bonnet next to the headlights. 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). These inputs allow the module to control manual control of the headlights. If equipped, it can also control automatic headlights, including day / night operation and high / low beam. Refer to your specific vehicle handbook to determine which door is marked "A" in your particular 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 may or may not be serious, depending on what the problem is. The manufacturer could manually correct the problem in the event of a bus failure.
Symptoms of a U0241 code may include:
- Headlights never turn on / off
- Headlights never react to low / high beam request
- HCM-A does not turn on / does not work
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 HCM-A
- 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 U0241 code before any of the underlying codes are thoroughly diagnosed and corrected.
If the only code you get from other modules is U0241, try accessing HCM-A. If you can access codes from HCM-A then code U0241 is either intermittent or memory code. If the HCM-A cannot be accessed, then code U0241 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 headlight control module a.
Check all fuses supplying HCM-A on this vehicle. Check all the reasons for HCM-A. 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 HCM-A module. If communication with HCM-A recovers, the problem is most likely a fuse / connection issue.
If the code returns or communication with the module is still not established, locate the CAN bus communication connections on your vehicle, primarily the HCM-A connector, which is usually located behind the dashboard next to the headlight switch. can also be installed under the bonnet next to the headlights. Disconnect the negative battery cable before disconnecting the connector on the HCM-A. 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 HCM-A. You will need access to a digital volt/ohmmeter (DVOM). Make sure HCM-A has power and ground. Access the wiring diagram and determine where the main power and ground supplies enter the HCM-A. Connect the battery before continuing with the HCM-A still disconnected. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply included in the HCM-A connector, and the black lead of your voltmeter to a good ground (if 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 if you were unable to reset DTC U0241, the only thing to do is to seek help from a trained automotive diagnostician, as this will indicate an HCM-A failure. . Most of these HCM-A's must be programmed or calibrated in order to fit properly on the vehicle.
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