U0198 Lost Communication With Telematic Control Module

U0198 Lost Communication With Telematic Control Module

OBD-II DTC Datasheet

Lost Communication With Telematic Control Module

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 that the telematics control module (TCM) 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.

The telematics control module (TCM) is usually located behind the dashboard, usually in the center of the vehicle. It can also be found in the rear of the car in the trunk or rear storage compartment. 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 display correct route information by calculating the vehicle position and sending this information over the data bus to the navigation module or to the instrument cluster / main display system.

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 can be serious if the TCM sends incorrect data to the display module / system, thereby providing incorrect navigation information.

Symptoms of a U0198 code may include:

• TCM provides no information / sound / possibly blank screen
• TCM 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 TCM
• 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 U0198 code before any of the underlying codes are thoroughly diagnosed and corrected.

If the only code you get from other modules is U0198, try accessing the TCM. If you can access the codes from the TCM, then code U0198 is either an intermittent or memory code. If the TCM cannot be accessed, then code U0198 that other modules set is active and the problem already exists.

The most common failure is a circuit failure that results in loss of power or ground to the telematics module.

Check all fuses supplying the TCM on this vehicle. Check all grounds for TCM. 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 TCM. If communication with the TCM recovers, the problem is most likely a fuse / connection issue.

If the code returns or communication with the module still fails, locate the CAN bus communication connections on your vehicle, most notably the TCM connector, which is usually located behind the dashboard, usually in the center of the vehicle. can also be found in the rear of the car in the trunk or rear storage compartment. Disconnect the negative battery cable before disconnecting the connector on the TCM. 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 TCM. You will need access to a digital volt/ohmmeter (DVOM). Make sure the TCM has power and ground. Access the wiring diagram and determine where the main power and ground supplies enter the TCM. Connect the battery before proceeding with the TCM disabled. Connect the red lead of your voltmeter to each B+ (battery voltage) supply going into the TCM 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 you were unable to clear DTC U0198, the only thing that can be done is to seek help from a trained automotive diagnostician, as this will point to a faulty TCM. Most of these TCMs must be programmed or calibrated to properly install the vehicle.

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