U0197: Lost Communication With Telephone Control Module

What it means

A control module is not receiving expected messages from the Telephone Control Module. Telephone-related functions may be unavailable; the code alone does not identify why communication was lost.

How it works

The Telephone Control Module supports vehicle telephone functions such as hands-free communication and exchanges messages over the vehicle network. U0197 sets when the reporting module misses the telephone module's expected messages for its timeout period.

Common causes

Most likely first.

1. Hands-free module unpowered
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Telephone-related functions may be unavailable
• Other communication codes

How to diagnose it

1. Scan all modules and save freeze-frame data and related communication codes to determine whether the telephone module alone is missing or other network nodes are affected.
2. Check battery condition and system voltage, then see whether the hands-free system powers up.
3. Inspect the telephone module's power, ground, and CAN connectors for corrosion, loose fit, or damaged wiring.
4. Use the wiring diagram to check the network branch to the telephone module for open or short circuits.
5. If wiring and power are sound, check gateway communication status and measure network termination only at specified test points against the manufacturer's specification.

Common fixes

• Restore power or ground to the hands-free telephone module.
• Reseat or clean its network connector.
• Repair damaged CAN wiring to the telephone module.
• Correct a gateway routing or network termination fault confirmed by testing.
• Replace or reprogram the telephone control module if it fails after power, ground, and network checks.

Can I keep driving?

Hands-free telephone functions may be unavailable, but this code alone usually does not prevent driving. If an emergency calling feature is affected, do not rely on it until communication is restored.