U04A4Invalid Data Received From Particulate Matter Sensor A
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Diesel particulate matter (PM) sensors have their own control unit that measures soot on the element and sends the result to the engine controller. GM's 2025 ECM tables (25OBDG04A) check the alive rolling count, protection value and checksum of about twenty soot sensor signals and set U04A4 after 3 bad frames in 10, with battery voltage of at least 11 V for 5 s; it is a Type B code, so the MIL comes on after two trips. VW's 2014 Touareg TDI chart sets it when the sensitivity factor leaves 0.75 to 1.25, when an invalid sensitivity signal lasts 2 s or when sensor messages fail for 0.6 s. Ford's 2014 chart also lists it as a MIL code. U02A3 is total loss, U04B2 the second sensor, U05A4 the reverse direction. The filter monitor pauses until data are valid.
- What you may notice
- Check engine light on
- Particulate filter monitor not completing, readiness missing
- Usually no change in how the engine runs
- Likely causes
- LikelyPM sensor control unit or sensing element faulty (heat, soot, moisture)
- PossibleReplacement sensor of the wrong variant or not yet matched
- PossibleDamaged wiring or connector between sensor unit and engine controller
- RareLow supply voltage disturbing the sensor unit
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €150 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.