Powertrain, generic · Hybrid propulsion

P0C40 DC/DC Converter Temperature Sensor B High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P0C40 means the second temperature sensor of the DC/DC converter delivers a voltage above its valid window, which on a thermistor circuit points to a short to positive or an open line pulled up to the reference. Mercedes-Benz documents it for the EQB (series 243) and the G-Class including the electric G 580 (series 465). Information LI54.10-P-079533 describes P0C4000 as a short to positive of temperature sensor B and lists it among up to four converter codes, with P0C3B00, P0E9700 and P0E5400, that appear after the converter wakes up incorrectly. The car shows a red 12 V battery message plus HV warnings. Workshops check the converter with XENTRY, erase the memory and reset the unit before replacing anything. P0C3F is the low counterpart; sensor A uses P0C3B.

Likely causes

Converter entering a fault state after incorrect wake-up (Mercedes 243/465)
Open circuit or short to positive in the sensor B wiring
Internal defect of the DC/DC converter

Symptoms

  • Red 12 V battery message in the instrument cluster
  • White or yellow high-voltage warning
  • 12 V battery no longer charged while driving

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€80–2,500
Time0.5–4 h

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

Parts involved

dcdc converter temp sensor bwiring harnessdcdc converter

Related codes

P0C3DP0C3EP0C3FP0C41P0C3BP0E54

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