Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P05EB Cold Start SCR NOx Catalyst Inlet Temperature Too Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

After a cold start a diesel heats its exhaust actively – retarded and post injection, intake or exhaust throttling, higher idle, EGR cooler bypass – so the SCR catalyst quickly reaches the temperature at which urea dosing can start (around 180–200 °C). P05EB sets when the measured temperature at the SCR inlet stays below the expected or modelled value within a set time after the start: the heating strategy is not working. CARB requires this 'catalyst warm-up' monitor for light-duty diesels from model year 2026 (20 %) to 2028 (100 %); GM 2025 and Ford 2023 tables do not contain the code yet. Volvo Trucks used it on 2016–17 heavy-duty engines and advised a software check instead of replacing parts. The lamp comes on; no power limitation from this code alone is known.

Likely causes

Engine module software or calibration (false trigger)
Exhaust temperature sensor before the SCR reads low or slow
Heating measure not effective: throttle, EGR cooler bypass or turbo vanes sticking
Post or retarded injection not effective (injectors)
Exhaust leak before the sensor or extremely cold conditions

Symptoms

  • Check engine light on
  • Usually no driving symptoms
  • Higher NOx emissions after cold start (not noticeable)

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–800
Time1–4 h

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

Parts involved

exhaust temperature sensorscr catalystengine control module

Related codes

P050EP05ECP20EEP0544P2080

References: law.cornell.edu, static.nhtsa.gov.