P20EDSCR NOx Pre-Catalyst Over Temperature (Bank 1)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P20ED applies to systems with two SCR stages in series: a small pre-catalyst mounted close to the engine, often with its own dosing unit, ahead of the main SCR brick. The code says this front stage on bank 1 got hotter than permitted. Paccar's patent US11976582 explains why such close-coupled SCR units exist: they sit where exhaust heat arrives first, so they work soon after a cold start, but for the same reason they see the highest temperatures, including those released by the oxidation catalyst during filter regeneration. Vanadium formulations begin to sublimate above about 550 °C, and 40 CFR 1036.115 obliges heavy-duty engine makers to keep the catalyst below such limits. No manufacturer documents P20ED publicly. P20EC is the same fault on the main catalyst. Expect the MIL; damage later shows as P20EF.
- What you may notice
- Malfunction indicator lamp on
- Front SCR dosing stopped or regeneration interrupted
- Higher NOx emissions after a cold start
- Likely causes
- LikelyHeat from oxidation catalyst or filter regeneration reaching the close-coupled stage
- PossibleFuel or oil entering the exhaust upstream of the pre-catalyst
- PossibleTemperature sensor at the pre-catalyst reading too high
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.