P0A05: Motor Electronics Coolant Pump A Control Circuit/Open

The electric pump that circulates coolant through the inverter, converter and drive motor loop is driven by a control line from the hybrid module. P0A05 means that line shows an open circuit or a fault the driver cannot classify further. No manufacturer documents P0A05 publicly. GM's Chevrolet Volt tables cover the same pump under P0CE9, set when the control line is open or shorted in 16 of 20 samples at 250 ms, Type B with MIL after two trips. CARB requires inverter cooling outputs to be checked, and Toyota patents describe how pump faults are told apart from other cooling faults. Low and high faults are P0A06 and P0A07; pump B is P0B38. Without circulation the electronics heat up quickly and power is cut.

Medium severity. Can I keep driving?Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

Symptoms

Hybrid system warning or check engine light
Electric drive power reduced, especially in warm weather or under load
Follow-up inverter overtemperature codes such as P0A93

Most likely causes

Pump connector loose or corroded, often from road splash at the low-mounted pump
Broken control wire between module and pump
Failed electronics or open winding inside the pump
Blown pump fuse or missing supply, so the control input sees no load

What to check, in order

Start with the simplest. You can tick off each step.

With the engine cold, check the coolant level; never do this when the system is hot
Check the continuity of the wire between the component and the control module.
Check the actual temperature in live data
Make sure the fan comes on when it should
Check the thermostat and connector
Measure the sensor and replace it if its readings do not make sense

Good to know

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

What each character of P0A05 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
A: Hybrid or air and fuel
05: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0A05?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P0A05?

The most common causes are: pump connector loose or corroded, often from road splash at the low-mounted pump; broken control wire between module and pump; failed electronics or open winding inside the pump.

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.