U0124 Lost Communication With Lateral Acceleration Sensor Module (LAS)

U0124 Lost Communication With Lateral Acceleration Sensor Module (LAS)

OBD-II DTC Datasheet

Lost Communication With Lateral Acceleration Sensor Module (LAS)

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 Lateral Acceleration Sensor (LAS) module 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 LAS module is responsible for preventing the loss of tire and vehicle control when cornering on wet asphalt or during aggressive driving.

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.

symptoms

Symptoms of a U0124 engine code may include:

• Malfunction Indicator Lamp (MIL) illuminated
• ABS indicator is on
• TRAC indicator is on (depending on the manufacturer)
• ESP / ESC indicator is on (depending on the manufacturer)

reasons

Usually the reason for installing this code is:

• Loss of power or ground to the LAS module (most common)
• 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
• 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 U0124, try accessing the LAS module. If you can access the codes from the LAS module, then code U0124 is either intermittent or a memory code. If the codes for the LAS module cannot be accessed, then code U0124 set by other modules is active and the problem already exists.

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

Check all fuses supplying the LAS module on this vehicle. Check all grounds for the LAN module. 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 U0124 returns or you can contact the LAS module. 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 LAS module connector. Disconnect the negative battery cable before disconnecting the connector on the LAS control 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 connecting the connectors back to the LAS module. You will need access to a digital volt/ohmmeter (DVOM). Make sure you have power and ground on the LAS module. Access the wiring diagram and determine where the main power and ground supplies enter the LAS module. Connect the battery before continuing with the LAS module still disabled. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply plugged into the LAS module connector, and the black lead of your voltmeter to a good ground (if unsure, battery negative always works). You 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 U0124, the only thing that can be done is to seek help from a trained automotive diagnostician as this will indicate a faulty LAS module. Most of these LAS modules need to be programmed or calibrated for the vehicle in order to be properly installed.

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