Network, generic

U01B1 Lost Communication With Particulate Matter Sensor B

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Heat-damaged or corroded harness or connector at sensor B near the exhaust
Sensor control unit without supply voltage or ground (fuse, relay)
Control unit of PM sensor B faulty

Symptoms

  • MIL on
  • Particulate filter monitor shows as not complete

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–600
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

pm sensor bcan bus

Related codes

U02A3U04B2U04A4U05A4

References: law.cornell.edu, gsi.ext.gm.com.