U04B2 code meaning
Invalid Data Received From Particulate Matter Sensor B
Network system Generic code U04xx codes Check engine light
What U04B2 means
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.
U04B2 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of U04B2
- Check engine light on
- Particulate filter readiness not set
Common causes of U04B2
- Most likelyControl unit or element of PM sensor B damaged by heat, soot or moisture
- PossibleWiring or connector of sensor B chafed or corroded
- Less likelySensors A and B swapped or wrong variant fitted
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Pm sensor b
What each part of U04B2 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B2 | The exact fault in that area. |
What to do next
- Note U04B2 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 U04B2
What does U04B2 mean?
U04B2 means "Invalid Data Received From Particulate Matter Sensor B". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with U04B2?
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 U04B2 fail an emissions test?
Yes, it can. U04B2 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 U04B2 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. This is a job for a workshop.
Will U04B2 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.