U01B1 code meaning
Lost Communication With Particulate Matter Sensor B
Network system Generic code U01xx codes Check engine light
What U01B1 means
U01B1 concerns a second particulate matter sensor in a diesel exhaust, used where a layout needs two of them. Such smart sensors carry their own control unit, which heats the element, measures soot build-up and sends the results to the engine controller over CAN. U01B1 is stored when that controller stops receiving frames from sensor B. No manufacturer documents this code publicly. For the single sensor, GM's 2025 tables (25OBDG04A) set the counterpart U02A3 after more than 10 s without its messages, Type B, which shows how the check works. CARB 1968.2 relies on the PM sensor to prove filter efficiency, so without sensor B the filter monitor for its branch cannot finish. Expect a MIL and no change in how the car drives; U04B2 applies if frames arrive with invalid content.
U01B1 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of U01B1
- MIL on
- Particulate filter monitor shows as not complete
Common causes of U01B1
- Most likelyHeat-damaged or corroded harness or connector at sensor B near the exhaust
- PossibleSensor control unit without supply voltage or ground (fuse, relay)
- PossibleControl unit of PM sensor B faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Pm sensor bCAN bus
What each part of U01B1 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B1 | The exact fault in that area. |
What to do next
- Note U01B1 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 U01B1
What does U01B1 mean?
U01B1 means "Lost Communication With Particulate Matter Sensor B". U01B1 concerns a second particulate matter sensor in a diesel exhaust, used where a layout needs two of them. It is a generic code, so it means the same on every make.
Is it safe to drive with U01B1?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U01B1 fail an emissions test?
Yes, it can. U01B1 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U01B1 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will U01B1 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.