P0C3F: DC/DC Converter Temperature Sensor B Low

P0C3F is stored when the voltage from the second temperature sensor of the DC/DC converter falls below the lowest plausible value. These sensors are normally NTC thermistors fed through a pull-up resistor, so a low voltage corresponds to an extremely hot reading; a short to ground or a shorted element produces exactly that. No manufacturer documents P0C3F publicly. GM uses the same logic for comparable hybrid thermistors, flagging a low circuit once the computed temperature reaches about 88 °C. Mercedes-Benz lists the opposite fault of the same sensor, P0C40, on the EQB and G-Class. CARB requires hybrid component inputs to be checked for out-of-range signals. The converter usually derates to protect itself, so 12 V charging suffers. Sensor A's low code is P0C3A.

Symptoms

• Hybrid or EV system warning in the cluster
• 12 V battery warning or falling on-board voltage
• Reduced power or switched-off comfort consumers

Most likely causes

• Sensor B signal line shorted to ground in the converter or harness
• Shorted thermistor B, usually only fixable by replacing the converter
• Converter actually overheating because its cooling fails

What to check, in order

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

1. Read the codes with a hybrid-compatible scanner and write down the freeze frame data
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Make sure the battery cooling air intake is clean
4. Check the 12 V auxiliary battery, which can also trigger warnings
5. 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 P0C3F means

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

Frequently asked questions

Can I keep driving with code P0C3F?

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 P0C3F?

The most common causes are: sensor B signal line shorted to ground in the converter or harness; shorted thermistor B, usually only fixable by replacing the converter; converter actually overheating because its cooling fails.

Related codes

• P0C3DDC/DC Converter Temperature Sensor B Circuit
• P0C3EDC/DC Converter Temperature Sensor B Range/Performance
• P0C40DC/DC Converter Temperature Sensor B High
• P0C41DC/DC Converter Temperature Sensor B Intermittent/Erratic
• P0C3ADC/DC Converter Temperature Sensor A Low
• P0D32DC/DC Converter A Over Temperature

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 19OBDG01 Hybrid Diagnostics
• static.nhtsa.gov: MC 11021800 0001

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.