Powertrain, generic (extended)

P2BA4 Catalyst Feedgas Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Many diesel SCR systems rely on the oxidation catalyst ahead of them to turn part of the NO into NO2, because a mix near half NO2 lets the SCR reaction run fast at low temperature. P2BA4 reports that this catalyst no longer delivers the needed gas mix. CARB 13 CCR 1968.2 (f)(1.2.3)(B) requires this check for 2015 and later diesels, but lets a maker cover it with the regular NMHC efficiency monitor; Ford's 2023 diesel summary does exactly that via P0420. GM and Cummins patents describe two methods: comparing SCR efficiency measured by the NOx sensors, or judging the catalyst's light-off heat after a hydrocarbon dose. No maker documents P2BA4 publicly. P2BA5 is the same check for a coated particulate filter; the driver mainly notices a lit MIL and possibly SCR codes.

Likely causes

Oxidation catalyst thermally aged or poisoned (sulphur, oil ash), little NO2 produced
Catalyst inlet face coated with soot or unburnt fuel after injector or EGR problems
Faulty NOx or exhaust temperature sensor distorting the evaluation
Exhaust leak upstream of the catalyst diluting the measured gas

Symptoms

  • Malfunction indicator lamp on
  • SCR efficiency codes such as P20EE set as well
  • Usually no noticeable change in driving behaviour

Repair estimate

DifficultyHardWorkshop job
Parts and labour€300–2,500
Time1–4 h

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

Parts involved

diesel oxidation catalystscr catalystecm

Related codes

P2BA5P0420P20EEP2BA6

References: law.cornell.edu, patents.google.com, patents.google.com, patents.google.com.