U0209 Lost Communication With Seat Control Module B

U0209 Lost Communication With Seat Control Module B

OBD-II DTC Datasheet

Lost Communication With Seat Control Module 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 Seat 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.

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.

Seat Control Module B (SCM-B) is usually located behind the flap next to the seat in question. Can also be found attached to the bottom of the seat in question. It receives input from a variety of sensors, some of which are directly connected to it, and most are sent over a bus communication system from the powertrain control module (PCM). These inputs allow the module to control the position of the driver / passenger seat.

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 never serious, as this is a device for the convenience of customers. The lack of SCM-B operation does not in any way affect the operation of the vehicle.

Symptoms of a U0209 code may include:

• Driver / passenger seat stuck in one position / does not move
• SCM-B 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 SCM-B
• 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 U0209 code before any of the underlying codes are thoroughly diagnosed and corrected.

If the only code you get from other modules is U0209, try accessing the SCM-B. If you can access the codes from the SCM-B, then code U0209 is either intermittent or a memory code. If the SCM-B cannot be accessed, then code U0209 set by other modules is active and the problem already exists.

The most common fault is a circuit fault that cuts power or ground to the seat control module. 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 diagnostic trouble codes from any modules that set the code in memory and see if you can now communicate with the SCM-B module. If communication with the SCM-B recovers, the problem is most likely a fuse / connection issue.

If the code returns or communication with the module still cannot be established, locate the CAN bus communication connections on your vehicle, most importantly the SCM-B connector, which is usually located behind the flap next to the seat in question. can also be attached to the bottom of the seat in question. 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 connecting the connectors back to 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 main power and ground supplies enter the SCM-B. Connect the battery before continuing with the SCM-B still disconnected. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply included in the SCM-B 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 are unable to reset DTC U0209, the only thing you can do is seek help from a trained automotive diagnostician, as this will indicate an SCM-B failure. . Most of these SCM-Bs must be programmed or calibrated to fit properly in a 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 U0209 code?

If you still need help with DTC U0209, 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.