P2C66: Hybrid/EV Electronics Coolant Pump A Underspeed

What it means

The hybrid electronics coolant pump A runs below the calibrated minimum speed for the commanded duty. Mechanical resistance high or supply voltage low.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

Hybrid/EV electronics coolant pump A circulates coolant to remove heat from power electronics. The hybrid control module compares the pump's speed with the commanded duty and sets this code when pump A turns below the minimum speed expected for that command.

Common causes

Most likely first.

1. Mechanical load increased
2. Supply voltage low under load

Symptoms

• Check-engine light or hybrid-system warning
• Reduced hybrid power or performance
• Hybrid-system temperature warning

How to diagnose it

1. Read freeze-frame data and hybrid-system live data for pump A command, reported speed, temperature warnings, and supply voltage when the fault occurred.
2. Inspect the pump A coolant loop for leaks, restricted hoses, or other visible signs of increased mechanical load.
3. Check pump A connectors, wiring, and grounds for looseness, corrosion, or damage.
4. Have the pump supply voltage checked under load against the manufacturer's specification, since low voltage can reduce speed.
5. If power and wiring are correct, test pump A operation and mechanical resistance using the manufacturer's procedure.

Common fixes

• Secure or repair a loose, corroded, or damaged pump A electrical connection.
• Repair a damaged supply or ground wire.
• Correct a restriction or mechanical load in the pump A coolant loop.
• Replace pump A if it cannot reach the commanded speed with correct power and an unobstructed loop.

Can I keep driving?

Because this fault can reduce cooling and trigger reduced hybrid power, avoid demanding acceleration and stop safely if a hybrid temperature warning appears. Do not continue driving with an overheating warning; the electronics may be damaged.