Motor Electronics Coolant Pump Control Circuit Low
The P0B39 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the control circuit of the motor electronics coolant pump. This pump is responsible for circulating coolant through the inverter and electric drive motor in hybrid and electric vehicles. A low circuit voltage typically points to a wiring issue, a faulty pump, or a problem with the PCM itself. If left unaddressed, it can lead to overheating of the motor electronics, potentially causing reduced performance or component damage.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Overheating of the electric drive motor or inverter
- Reduced vehicle performance or limp mode
- Coolant pump not running or running intermittently
2. Most Common Causes
- Faulty motor electronics coolant pump
- Open or shorted wiring in the pump control circuit
- Poor electrical connection at the pump or PCM
- Failed PCM (rare)
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the coolant pump and its wiring harness for damage or corrosion.
Step 3: Test the pump's control circuit voltage with a multimeter; compare to manufacturer specifications.
Step 4: Check the pump's resistance and operation by applying battery voltage directly.
Step 5: If wiring and pump are okay, test the PCM output signal or replace the PCM.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a low circuit voltage can cause the coolant pump to fail, leading to overheating of the motor electronics and potential damage to expensive components.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, but can be higher if the pump or PCM needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.