Auxiliary Transmission Fluid Pump Motor Phase U Circuit Malfunction
The P0B00 code indicates a fault in the phase U circuit of the auxiliary transmission fluid pump motor. This pump is typically found in hybrid or electric vehicles to circulate transmission fluid when the main engine is off. The issue may stem from an open or short circuit in the motor windings, a faulty pump motor, or a problem with the transmission control module. This can lead to inadequate fluid circulation, potentially causing transmission overheating or damage.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission overheating or slipping
- Reduced fuel economy in hybrid vehicles
- Vehicle may enter limp mode
2. Most Common Causes
- Open or short circuit in the auxiliary transmission fluid pump motor phase U wiring
- Faulty auxiliary transmission fluid pump motor
- Damaged connector or poor electrical connection
- Transmission control module (TCM) failure
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all stored codes and freeze frame data.
Step 2: Visually inspect the auxiliary pump wiring and connectors for damage, corrosion, or loose connections.
Step 3: Measure resistance across phase U of the pump motor and compare to specifications.
Step 4: Test the pump motor operation by applying power directly (if safe) or using a diagnostic tool.
Step 5: If wiring and motor are okay, check the TCM for faults or perform a software update.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a faulty auxiliary pump can cause 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 $50 to $150 for diagnosis and minor repairs like wiring fixes. Replacing the pump motor can cost $200-$500 or more, depending on the vehicle.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.