What Does P0A05 Mean?
The hybrid/EV powertrain control module has detected a fault in the motor electronics coolant pump 'A' control circuit, specifically an open circuit condition. This electric pump circulates coolant through the inverter, DC-DC converter, and other power electronics. Without proper pump operation, these components will overheat rapidly under load.
Safety Warning
Without coolant pump operation, power electronics will overheat quickly under load, potentially causing permanent damage to the inverter. Do not drive under electric power until repaired.
Common Causes
30%
Motor electronics coolant pump A motor failure (open winding)
30%
Open circuit in the pump control wiring or disconnected connector
25%
Blown fuse or failed relay in the coolant pump power supply circuit
15%
Control module pump driver circuit failure
Diagnostic Steps
1
Step 1: Check the fuse and relay for the motor electronics coolant pump in the HV fuse box. Replace any blown fuse and test the relay by swapping with an identical one.
2
Step 2: Locate the coolant pump A and verify the connector is securely attached. Inspect for damage, corrosion, or coolant contamination at the connector.
3
Step 3: Measure voltage at the pump connector with the pump commanded on (use bidirectional scan tool control). Battery voltage (or HV as applicable) should be present. If absent, trace the power feed.
4
Step 4: If voltage is present at the connector, measure pump motor resistance. An OL reading indicates a failed pump motor. Typical resistance varies by manufacturer.
5
Step 5: Verify the ground circuit from the pump back to the control module or chassis is intact with less than 1 ohm resistance.
Estimated Repair Cost
$300 - $1,200
Parts + labor, varies by vehicle and location
The hybrid/EV powertrain control module has detected a fault in the motor electronics coolant pump 'A' control circuit, specifically an open circuit condition. This electric pump circulates coolant through the inverter, DC-DC converter, and other power electronics. Without proper pump operation, the...
The most common cause of P0A05 (Motor Electronics Coolant Pump "A" Control Circuit/Open) is: Motor electronics coolant pump A motor failure (open winding)
Typical repair costs for P0A05 range from $300 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Without coolant pump operation, power electronics will overheat quickly under load, potentially causing permanent damage to the inverter. Do not drive under electric power until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0A05 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid/EV Motor Electronics Cooling
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
