What Does P0B38 Mean?
The powertrain control module has detected an open circuit or general fault in the motor electronics coolant pump "B" control circuit. This pump is responsible for circulating coolant through the power electronics (inverter, DC-DC converter) in the hybrid/EV system. Without proper cooling, these components can overheat and fail catastrophically.
Safety Warning
Do not drive. Without coolant pump operation, the motor electronics can overheat within minutes, causing permanent damage to the inverter and potentially creating a fire hazard.
Common Causes
35%
Failed coolant pump B motor with open winding or seized impeller
30%
Open circuit in the pump control wiring harness from disconnected or corroded connector
20%
Blown fuse or failed relay in the pump B power supply circuit
15%
Powertrain control module driver circuit failure for pump B output
Diagnostic Steps
1
Step 1: Check the fuse and relay for coolant pump B in the EV/hybrid fuse box. Replace any blown fuse and test relay operation by swapping with an identical relay.
2
Step 2: At the coolant pump B connector, measure supply voltage with KOEO (Key On Engine Off). Battery voltage should be present on the power wire. If not, trace the power circuit for opens.
3
Step 3: Measure the pump motor winding resistance at the pump connector (disconnect first). Expected resistance is typically 1-10 ohms depending on manufacturer. Open reading (OL) confirms pump failure.
4
Step 4: Verify the control signal from the PCM to the pump by back-probing the control wire and commanding the pump on via scan tool bidirectional controls. A PWM signal should be present.
5
Step 5: If power, ground, and control signals are all present at the pump but it does not operate, the pump motor has failed and requires replacement.
Estimated Repair Cost
$200 - $1,200
Parts + labor, varies by vehicle and location
The powertrain control module has detected an open circuit or general fault in the motor electronics coolant pump "B" control circuit. This pump is responsible for circulating coolant through the power electronics (inverter, DC-DC converter) in the hybrid/EV system. Without proper cooling, these com...
The most common cause of P0B38 (Motor Electronics Coolant Pump "B" Control Circuit/Open) is: Failed coolant pump B motor with open winding or seized impeller
Typical repair costs for P0B38 range from $200 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Do not drive. Without coolant pump operation, the motor electronics can overheat within minutes, causing permanent damage to the inverter and potentially creating a fire hazard.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B38 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid/EV Thermal Management System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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