OBD CodesWhat it means
Each of these codes is set by one computer saying that another has gone silent on the data bus. The silent module may have lost its power or earth, its connector may be loose, or it may have failed.
Codes in this group
| Code | Meaning |
|---|---|
| U0100 | No communication with the engine computer |
| U0101 | No communication with the transmission computer |
| U0102 | No communication with the transfer case module |
| U0103 | No communication with the gear shift module |
| U0121 | No communication with the ABS module |
| U0131 | No communication with the power steering module |
| U0140 | No communication with the body control module |
| U0151 | No communication with the airbag module |
| U0155 | No communication with the instrument cluster |
| U0164 | No communication with the climate control module |
Bank 1 is the side of the engine that has cylinder 1. Sensor 1 is before the catalytic converter and sensor 2 is after it. More terms explained.
What you may notice
- Warning light for the system that has gone silent (ABS, airbag, steering)
- That system not working
- No-start if the engine computer is the silent one
Common causes
Most likely first:
- A blown fuse feeding the module
- A loose, wet or corroded connector
- Low battery voltage
- A failed module
- Damaged bus wiring to that module
What to check first
- Check the fuses for the module named
- Check battery condition
- If the airbag or ABS module is silent, those safety systems may not work: have it repaired promptly
Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.
After the repair
Once the cause is fixed, the code can be cleared with a scan tool, or the warning light goes out by itself after several trips without the fault. Clearing a code without fixing the cause only hides it for a while. More about clearing codes.
Related codes
CAN data bus fault (U0001), Invalid data received from a control module (U0401). All codes.
Written in November 2026. These are generic OBD-II codes, the same on all makes. Causes and repair steps differ between models.