Powertrain, generic · Hybrid propulsion

P0A05 Motor Electronics Coolant Pump A Control Circuit/Open

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

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.

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

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

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€100–800

Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

motor electronics coolant pump awiring harnesshybrid control module

References: law.cornell.edu, patents.google.com, gsi.ext.gm.com.