P0C40 code meaning
DC/DC Converter Temperature Sensor B High
Powertrain system Generic code P0Cxx codes Check engine light
What P0C40 means
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.
P0C40 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0C40
- Red 12 V battery message in the instrument cluster
- White or yellow high-voltage warning
- 12 V battery no longer charged while driving
Common causes of P0C40
- Most likelyConverter entering a fault state after incorrect wake-up (Mercedes 243/465)
- PossibleOpen circuit or short to positive in the sensor B wiring
- Less likelyInternal defect of the DC/DC converter
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Dcdc converter temp sensor bWiring harnessDcdc converter
What each part of P0C40 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| C | Area: hybrid propulsion. |
| 40 | The exact fault in that area. |
What to do next
- Note P0C40 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0C40
What does P0C40 mean?
P0C40 means "DC/DC Converter Temperature Sensor B High". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0C40?
Drive gently and only to a workshop. With P0C40 the car can go into limp mode (reduced power) to protect itself.
Will P0C40 fail an emissions test?
Yes, it can. P0C40 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0C40 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P0C40 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.