P0C31: Inverter B Cooling System Performance

P0C31 reports that the cooling circuit of a second power inverter does not remove heat as expected; inverter A has its own code, P0A93. Vehicles with two separately cooled power electronics units, for example a front and a rear drive unit, need this second code. CARB requires hybrid OBD to monitor the parts used for inverter thermal management and, where feasible, to check the cooling performance itself. No manufacturer documents P0C31 publicly. For the analogous P0A93, Hyundai's 2011 Sonata Hybrid bulletin 14-HC-001 points to the electric water pump, and coolant pump faults of the B circuit are reported as P0B38 or P0C74. To protect the semiconductors the controller limits motor power. A low coolant level or trapped air is worth checking first.

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

Hybrid or EV system warning and MIL
Reduced drive power, especially under load or in heat
Coolant level low in the electronics reservoir

Most likely causes

Low coolant level or air trapped in the inverter B circuit
Weak or failed electric coolant pump of the circuit
Clogged radiator or inoperative cooling fan

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
Compare the reading with other engine data while varying the engine speed.
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

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P0C31 means

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

Frequently asked questions

Can I keep driving with code P0C31?

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 P0C31?

The most common causes are: low coolant level or air trapped in the inverter B circuit; weak or failed electric coolant pump of the circuit; clogged radiator or inoperative cooling fan.

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.