U0139 Lost Communication With Suspension Control Module B

OBD-II DTC Datasheet

Lost Communication With Suspension Control Module "B"

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 the Suspension Control Module B (SCM-B) 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 SCM-B accepts 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 both vehicle height and shock / strut application, depending on the manufacturer's application. In some vehicles, the driver can choose a soft, hard or sporty ride depending on manual control or, in some cases, simply pressing the brake or accelerator pedal. If the brakes are firmly applied, or if the driver is accelerating quickly, the system can choose to drive hard instead of the previous default soft setting.

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. Normally, when the vehicle reaches ground clearance, the system is deactivated. As long as the failure occurs at this time, there should be no negative consequences for the safety of the vehicle / system / driving. If the failure is due to a compressor / ventilation / shock / strut failure, this could be a cause for concern as a safety issue could be popping up at any time if not already. In addition, safety is important when servicing these systems. ALWAYS refer to the service information before disassembling / diagnosing these systems.

Symptoms of a U0139 engine code may include:

Suspension warning lamp is on
Incorrect vehicle ground clearance
A rumbling is heard for a minute after every first key press.

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 SCM-B - the 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 U0139, try accessing the "B" suspension control module. If you can access the codes from the SCM-B, then code U0139 is either intermittent or a memory code. If the codes for the SCM-B cannot be accessed, then code U0139 set by other modules is active and the problem already exists.

The most common failure is a loss of power or ground to the SCM-B.

Check all fuses supplying the SCM-B on this vehicle. Check all grounds for SCM-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 U0139 returns or you can contact the SCM-B. If no code returns or connectivity 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 SCM-B connector. Disconnect the negative battery cable before disconnecting the connector on the SCM-B. 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 SCM-B. You will need access to a digital volt ohmmeter (DVOM). Make sure the SCM-B has power and ground. Access the wiring diagram and determine where the primary power and ground supplies go into the SCM-B. Reconnect the battery before proceeding with the SCM-B still disconnected. Connect the red wire of your voltmeter to each B + (battery voltage) power source going to the SCM-B 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 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 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 U0139, the only thing to do is to seek help from a trained automotive diagnostician, as this will indicate an SCM-B failure. module. Most of these SCM-Bs need to be programmed or calibrated for the vehicle in order to be properly installed.

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