Failing or worn coolant pump B (seized, weak or intermittent motor); Low coolant level or air trapped in the power electronics cooling circuit; Wiring or connector fault in the pump power, ground or control signal circuit (corrosion, chafing, loose pin); Blocked or restricted coolant hose, radiator or cooling passage reducing flow; Blown fuse or faulty relay supplying the pump; Faulty inverter or control unit driver circuit, or outdated control unit software where a known fault exists.

P0C74

Motor Electronics Coolant Pump B Control Performance.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
C: AreaHybrid propulsion
74: FaultThe specific fault in that area

What it means

P0C74 is the generic code for a performance fault in the control circuit of coolant pump B, the pump that cools the motor electronics (inverter and related power electronics) in a hybrid or electric vehicle. The control unit commanded the pump and saw feedback, such as speed, flow or temperature response, that did not match what it expected. Which pump is 'B' and how it is monitored depends on the model.

Symptoms

Warning lamp lit, often a hybrid or EV system fault message
Reduced power or limp mode, especially under heavy load
Inverter or power electronics running hot, or a temperature warning
Reduced or limited charging or regeneration
Coolant pump noisy, or silent when it should be running
Vehicle refusing to enter ready mode in some cases

Possible causes

Failing or worn coolant pump B (seized, weak or intermittent motor)likely
Low coolant level or air trapped in the power electronics cooling circuitlikely
Wiring or connector fault in the pump power, ground or control signal circuit (corrosion, chafing, loose pin)possible
Blocked or restricted coolant hose, radiator or cooling passage reducing flowpossible
Blown fuse or faulty relay supplying the pumppossible
Faulty inverter or control unit driver circuit, or outdated control unit software where a known fault existsrare

How to diagnose

Read all stored and pending codes and freeze frame data, noting temperatures, vehicle state and whether other cooling or inverter codes are present
Check the coolant level and condition when the system is cold and safe to open, and look for leaks, following the manufacturer's high-voltage safety precautions
Check the relevant fuse and relay, and inspect the pump wiring and connector for damage, corrosion, water ingress or poor pin tension
Listen and feel for the pump running when keyed on or when commanded, and confirm hoses are warm or flowing as expected
Use a scan tool's active test to command the pump and compare actual speed or feedback with the commanded value
Check supply voltage, ground and control signal at the pump connector against the manufacturer's data
Check for flow restrictions, kinked hoses or air locks, and bleed the system using the model-specific procedure
Check for software updates or technical bulletins for the model if the pump and circuit test good

How to fix

Replace coolant pump B if it fails the active test or electrical checks
Top up or replace coolant with the correct specification and bleed the circuit using the manufacturer's procedure
Repair or replace damaged wiring, terminals or connectors in the pump circuit
Clear blockages or replace restricted hoses or cooling components
Replace the faulty fuse or relay after finding why it failed
Update the control unit software if a known calibration issue applies, or repair the inverter or control unit after confirmed diagnosis

Can I keep driving?

High severity

Avoid driving, or limit it to a short, gentle trip to a workshop, as overheating power electronics can cause costly damage and sudden loss of power. If a temperature warning appears, stop safely and switch off.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.