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U04B2 Invalid Data Received From Particulate Matter Sensor B

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

U04B2 is the B counterpart of U04A4, intended for vehicles that carry a second smart PM sensor, for instance one per exhaust line or one ahead of and one behind a filter. Messages from sensor B still reach the engine controller, but their content is rejected. No manufacturer documents this code publicly; the public examples all use the single sensor A. By analogy with GM's handling of sensor A in 25OBDG04A, a receiver would count frames with a wrong rolling counter, protection value or checksum and set the code once too many fail within a short window. CARB 1968.2 demands that OBD detect PM sensor faults before the sensor can no longer serve filter monitoring. U01B1 means sensor B has gone silent. Expect a MIL and an incomplete filter check, with no change in drivability.

Likely causes

Control unit or element of PM sensor B damaged by heat, soot or moisture

Wiring or connector of sensor B chafed or corroded

Sensors A and B swapped or wrong variant fitted

Symptoms

Check engine light on
Particulate filter readiness not set

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€150–700

Time0.5–2 h

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

Parts involved

pm sensor b

Related codes

U01B1 U04A4

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