U012B code meaning
Lost Communication With Chassis Control Module B
What U012B means
U012B is the counterpart to U012A for a second chassis controller, labelled B. No manufacturer documents U012B in an openly available source, so its exact job (air suspension, damping, steering or another chassis task) depends on the vehicle. Logic follows the usual network rule that CARB requires and GM spells out for module A: a receiving controller expects a periodic message, and if it stays away for a calibrated time while supply and ignition are valid, the receiver stores the code for the silent partner. GM's tables for U012A list Type B on engine nodes and Type C on the transmission, so the warning lamp behaviour is maker specific. Invalid data from module B is U042C.
U012B at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U012B
- Chassis warning message in the cluster
- Functions handled by module B (e.g. suspension) unavailable
- Scan tool cannot reach module B
Common causes of U012B
- Most likelyFuse, power or ground of chassis module B interrupted
- PossibleDamaged bus line or connector to module B
- Less likelyChassis module B internally faulty or not programmed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Chassis module bCAN bus wiring
What each part of U012B means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 2B | The exact fault in that area. |
What to do next
- Note U012B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U012B
What does U012B mean?
U012B means "Lost Communication With Chassis Control Module B". U012B is the counterpart to U012A for a second chassis controller, labelled B. It is a generic code, so it means the same on every make.
Is it safe to drive with U012B?
U012B does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U012B fail an emissions test?
U012B is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U012B to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U012B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.