Auxiliary Transmission Fluid Pump Motor Phase U Current Low
The P0B01 code indicates that the powertrain control module (PCM) has detected a low current condition in phase U of the auxiliary transmission fluid pump motor. This pump is responsible for circulating transmission fluid to cool and lubricate the transmission, especially during stop-start events or when the engine is off. A low current reading suggests increased resistance or an open circuit in the motor windings, wiring, or connector for phase U, which can lead to reduced pump performance and potential transmission overheating.
01. Most Common Causes
- Faulty auxiliary transmission fluid pump motor
- Open or shorted wiring in phase U circuit
- Poor electrical connection at pump connector
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission overheating or slipping
- Reduced fuel economy due to increased transmission drag
- Transmission warning messages on dashboard
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the auxiliary pump connector and wiring for damage, corrosion, or loose pins.
Step 3: Measure resistance between phase U and ground, and between phases; compare to specifications (typically 0.5-2 ohms).
Step 4: Check for voltage supply and ground at the pump connector with the pump commanded on.
Step 5: If all tests pass, replace the auxiliary transmission fluid pump motor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Low pump motor current can lead to insufficient transmission fluid circulation, causing overheating and potential transmission damage. Have it diagnosed promptly.
How much does it cost to fix?▼
The cost typically ranges from $150 to $400, including parts (pump motor) and labor. Diagnosis may add $100-$150.