Auxiliary Transmission Fluid Pump Motor Phase V Current Fault
The P0B03 code indicates a malfunction in the auxiliary transmission fluid pump motor phase V current circuit. This pump is responsible for circulating transmission fluid when the engine is off (e.g., during start-stop events) to maintain lubrication and cooling. The diagnostic trouble code (DTC) is set when the powertrain control module (PCM) detects an abnormal current reading in phase V of the pump motor, which could be due to an electrical fault, mechanical binding, or pump failure.
01. Most Common Causes
- Faulty auxiliary transmission fluid pump motor
- Open or short circuit in the pump motor wiring or connector
- Failed pump motor control module or relay
- Low transmission fluid level or contamination
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission slipping or harsh shifting
- Reduced fuel economy due to start-stop system deactivation
- Transmission overheating or unusual noises from the pump area
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Inspect the auxiliary pump wiring and connector for damage, corrosion, or loose pins.
Step 3: Measure resistance and voltage at the pump motor connector per manufacturer specifications.
Step 4: Test the pump motor operation by applying direct battery voltage (if safe) or using a scan tool to command the pump on.
Step 5: Check transmission fluid level and condition; replace if contaminated.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the auxiliary pump failure can lead to transmission damage, especially in stop-and-go traffic or if the start-stop system is active.
How much does it cost to fix?▼
Repair costs typically range from $200 to $600, including parts and labor, depending on the vehicle make and model. The pump itself can cost $100-$300, plus diagnostic time.