P0C3B: DC/DC Converter Temperature Sensor A High

P0C3B reports a signal from DC/DC converter temperature sensor A above its valid range, typically a short to positive or an open circuit pulled up by the input. Mercedes-Benz documents it on series 243 (EQB) and 465 (G-Class, including the electric G 580): information LI54.10-P-079533 describes P0C3B00 as a short circuit to positive of temperature sensor A, stored together with P0E9700, P0E5400 and P0C4000 after faulty wake-up behaviour of the converter. Drivers see a red 12 V battery message and white or yellow HV warnings. The remedy is a converter check in XENTRY, clearing the fault memory and a converter reset; parts are not replaced first. The low-signal sibling is P0C3A, sensor B's high code is P0C40.

High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

Symptoms

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

Most likely causes

Faulty wake-up behaviour of the converter putting it into an error state (Mercedes 243/465)
Open circuit or short to positive in the sensor A circuit
Internal defect of the DC/DC converter

What to check, in order

Start with the simplest. You can tick off each step.

Read the codes with a hybrid-compatible scanner and write down the freeze frame data
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Make sure the battery cooling air intake is clean
Check the 12 V auxiliary battery, which can also trigger warnings
Leave any high-voltage measurements to a specialized repair shop

Good to know

It can trigger limp mode.
It affects emissions.

What each character of P0C3B means

P: Powertrain: engine and transmission
0: Generic code: same on every make
C: Subsystem depends on the code range
3B: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0C3B?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0C3B?

The most common causes are: faulty wake-up behaviour of the converter putting it into an error state (Mercedes 243/465); open circuit or short to positive in the sensor A circuit; internal defect of the DC/DC converter.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.