Powertrain, generic (extended)

P2606 Intake Air Heater B Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P2606 means heater B in the intake does respond, but the current it draws or the voltage drop across its circuit lies outside the window the engine controller expects. Mack documents P2604-7F and P2606-7F for 2014-2017 trucks with MP7, MP8 and MP10 engines and puts them down to extra circuit resistance from corrosion inside the master disconnect switch, so inspecting those contacts comes first. Volvo's 2020 software change log for heavy-truck engines lists P2606-7F next to the heater A code as a result of the preheater relay issue addressed by new EMS software. Unlike P2605, P2607 and P2608, the circuit is not open or shorted but merely implausible; P2604 is the same check for heater A. Cold starts may become sluggish and the engine may smoke white until warm.

Likely causes

Extra resistance from corroded contacts, e.g. in the master disconnect switch
Worn preheat relay contacts
Aged heater element with changed resistance
Outdated engine software (update published by the maker)

Symptoms

  • Sluggish cold starts
  • White smoke until the engine is warm
  • MIL on

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–700
Time0.5–3 h

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

Parts involved

intake air heater bheater relay

Related codes

P2604P2605P2607P2608P2609P2CE2

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