Network & communication
Definition only
Lights the check engine lamp
U01B9: Lost Communication With Switch Input Module C
Standardized SAE J2012 code · U01xx — Lost communication with modules
What does U01B9 mean?
ECU lost communication with switch input module C (collects switch signals — windows, lights, etc.).
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
- High Module unpowered
- Low Gateway module routing CAN messages incorrectly
- Low CAN terminating resistor (120 Ω) drifted out of spec
Likelihood is a general estimate across vehicles; your make and model may differ.
Add your car to see reports of U01B9 on the same make and model first.
U01B9 in the community
Ask about U01B9No one has posted about U01B9 yet
Share your vehicle, the tool you used and what you tested — the first thread helps everyone who searches for this code.
Describe your U01B9 problem