Auxiliary Transmission Fluid Pump Motor Supply Voltage Circuit/Open
The P0B09 code indicates a problem with the auxiliary transmission fluid pump motor supply voltage circuit. This pump is typically found in hybrid or electric vehicles to circulate transmission fluid when the main engine is off. The code is set when the powertrain control module (PCM) detects an open or short in the circuit, or the voltage is out of the expected range. This can lead to inadequate transmission fluid circulation, potentially causing transmission overheating or damage.
01. Most Common Causes
- Blown fuse or faulty relay for the auxiliary pump circuit
- Damaged wiring or connectors in the pump motor circuit
- Faulty auxiliary transmission fluid pump motor
- Failed PCM or control module
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission overheating or slipping
- Reduced fuel economy in hybrid vehicles
- Transmission fluid leaks near the pump area
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for related codes.
Step 2: Visually inspect the auxiliary pump fuse and relay; replace if blown.
Step 3: Check the wiring and connectors for damage, corrosion, or loose connections.
Step 4: Test the pump motor voltage supply and ground circuits with a multimeter.
Step 5: If circuits are okay, test the pump motor resistance and operation; replace if faulty.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code, as the auxiliary pump failure can lead to transmission overheating and damage, especially in stop-and-go traffic or when the engine is off in hybrids.
How much does it cost to fix?▼
The cost typically ranges from $150 to $400, including parts and labor. The pump itself can cost $100-$250, and labor is about $50-$150 depending on the vehicle.