P2D0B: Motor Electronics Coolant Pump C Overspeed/Air in System

What it means

Motor electronics coolant pump C reports a overspeed/air in system condition. Power electronics cooling is impaired.

At a glance

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

How it works

Motor electronics coolant pump C moves coolant through a power-electronics cooling loop. The control module monitors pump C's reported speed and operating behavior; this code sets when it detects overspeed behavior associated with air in the loop, which can make coolant circulation unreliable.

Common causes

Most likely first.

1. Air pocket in coolant loop
2. Coolant level low

Symptoms

• Check-engine or hybrid-system warning
• Power limited warning
• Reduced performance under load

How to diagnose it

1. Review freeze-frame data and live pump C speed and command to see whether the overspeed indication occurs continuously or during a particular operating condition.
2. With the vehicle safely powered down and cool, check the coolant level in the circuit serving pump C and look for evidence of a leak.
3. Inspect pump C's hoses and connections for leaks, loose joints, or restrictions that could allow air into the loop.
4. Look for signs of air or interrupted circulation in pump C's loop and bleed it only by the vehicle's specified procedure.
5. If the level and loop are correct, compare pump C's commanded and reported speed and inspect its speed feedback circuit using the manufacturer's procedure.
6. Check pump C's supply and control wiring for intermittent connection faults if the speed reading remains implausible.

Common fixes

• Top up the correct coolant and repair the leak that allowed the level to fall.
• Bleed trapped air from pump C's loop using the manufacturer's procedure.
• Repair loose or damaged pump C hoses and connections that admit air.
• Repair pump C speed-feedback wiring or replace the pump if its reported speed remains abnormal with a full, air-free loop.

Can I keep driving?

Avoid heavy loads until pump C's loop is full and circulating reliably, since air or low coolant can impair power-electronics cooling. Stop safely if power is limited or a hybrid-system warning appears.