P2D07: Motor Electronics Coolant Pump B Underspeed

What it means

Motor electronics coolant pump B reports a underspeed 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 B circulates coolant through power electronics such as the inverter. The control module compares pump B's reported speed with its commanded speed; this code sets when pump B runs slower than expected, reducing cooling flow.

Common causes

Most likely first.

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

Symptoms

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

How to diagnose it

1. Read freeze-frame data and live pump B command and speed to see when the underspeed occurs and whether it is continuous or load-related.
2. With the vehicle safely powered down, inspect pump B, its coolant hoses, and nearby wiring for damage, leaks, kinks, or signs of obstruction.
3. Check the coolant level and look for restrictions or contamination in pump B's loop that could increase mechanical load.
4. Inspect pump B's connectors and grounds for corrosion, looseness, or heat damage.
5. Measure pump B's supply voltage while it is commanded on and compare it with the manufacturer's specification to check for voltage drop under load.
6. If coolant flow and supply are adequate, test pump B's operation and speed feedback against the manufacturer's diagnostic procedure.

Common fixes

• Correct a low coolant level or restriction in pump B's cooling loop and bleed it using the vehicle's specified procedure.
• Repair a loose, corroded, or damaged pump B connector, ground, or wiring.
• Repair a supply issue that causes voltage to drop when pump B is under load.
• Replace pump B if it remains below commanded speed despite adequate supply and coolant flow.

Can I keep driving?

Avoid heavy loads and prolonged driving because reduced cooling can overheat power electronics and trigger power limitation. If a hybrid-system or power-limited warning appears, stop safely and arrange prompt diagnosis.