P0C40DC/DC Converter Temperature Sensor B High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Red 12 V battery message in the instrument cluster
- White or yellow high-voltage warning
- 12 V battery no longer charged while driving
- Likely causes
- LikelyConverter entering a fault state after incorrect wake-up (Mercedes 243/465)
- PossibleOpen circuit or short to positive in the sensor B wiring
- RareInternal defect of the DC/DC converter
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €80 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.