Code
U0198
MERCEDES-BENZ
U — Network/User
Lost Communication with Telematic Control Module
Views:
UK: 10
EN: 24
RU: 36
AI status
Completed
Completed
100%
Causes
- Blown fuse or loss of supply voltage to the telematic control module
- Poor or corroded ground or power connector at the module
- Open, shorted or intermittent CAN/LIN wiring between the module and vehicle network
- Faulty CAN bus termination or wrong bus baud rate
- Internal failure of the telematic control module
- Incorrect or corrupted module programming or firmware mismatch
Symptoms
- Telematics services non-functional (e.g., emergency call, remote services)
- Inability to communicate with the telematic module using a diagnostic tool
- One or more network-related warning messages in the instrument cluster
- Multiple U‑codes or other module communication fault codes present
- Possible intermittent operation of features controlled via telematics
- Vehicle may show ‘service’ or similar network fault indicators
What to check
- Read and record all stored DTCs from all control modules; note freeze frame and occurrence history
- Verify vehicle battery state-of-charge and system voltage (12V nominal; >12.4V with key on)
- Inspect and test fuses and relay(s) supplying the telematic module
- Visually inspect module connector(s) for corrosion, bent pins, water ingress, or damage
- Check and clean module ground(s); verify low resistance to chassis (
- Measure CAN bus voltages at the module connector with key ON: CAN_H and CAN_L idle and dominant levels
Signal parameters
- Vehicle battery/supply voltage to telematic module: ~12–14.5 V (key on/engine running)
- Module ground resistance to chassis: ideally
- CAN_H idle voltage ~2.5V (recessive); dominant ~3.5V
- CAN_L idle voltage ~2.5V (recessive); dominant ~1.5V
- Differential CAN bus idle ~0V; dominant differential ~2V
- Common CAN bus baud rates to check: typically 500 kbps or 250 kbps (verify OEM data)
Diagnostic algorithm
- Verify and record U0198 and any other stored codes using a Mercedes-capable scan tool; clear codes and attempt to reproduce.
- Confirm battery health and supply voltage to the telematic module; check and replace any blown fuses or faulty relays supplying the module.
- Perform a visual inspection of the telematic module connector and harness; disconnect and inspect pins for corrosion, bending or contamination.
- Verify module grounds: disconnect battery negative if required by OEM procedure and clean/secure ground connections.
- With ignition ON, measure CAN_H and CAN_L voltages at the module connector; compare to expected idle and dominant values.
- Measure termination resistance across CAN_H and CAN_L; if not approx. 60 ohms, trace for missing terminator or short.
- If bus voltages are abnormal, isolate sections of the network: disconnect suspected modules one at a time and monitor bus behavior to locate short or faulty node.
- Check for incorrect baud rate or bus configuration (use OEM wiring diagrams and network topology).
- If wiring, power and grounds are good but module remains unresponsive, verify software/firmware level and perform OEM reprogramming or module initialization as required.
- If reprogramming does not restore communication and harness checks are clear, consider module replacement following OEM pairing/security procedures.
- After any repair, clear codes and perform a full network scan and function check of telematics services.
Likely causes
- Lost 12V supply or blown fuse to the telematic control module
- Damaged or loose connector pins or ground at the module
- CAN bus short to battery/ground or open circuit on CAN_H or CAN_L
- Faulty module software, requiring reflash or replacement
- Failed telematic control module (less common than wiring/power faults)
Fault status
Status
Lost communication with Telematic Control Module — check module power, ground, and CAN/LIN network for faults before replacing module.
Repair difficulty: Hard
Diagnostic time: 1-4 hours
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