Auxiliary Transmission Fluid Pump Motor Phase V Current Low
The P0B04 code indicates that the powertrain control module (PCM) has detected a low current condition in phase V of the auxiliary transmission fluid pump motor. This pump is responsible for circulating transmission fluid to cool and lubricate the transmission, especially during start-stop events or when the engine is off. Low current in one phase suggests a fault in the motor winding, wiring, or connector, which can lead to reduced pump performance and potential transmission damage.
01. Most Common Causes
- Faulty auxiliary transmission fluid pump motor
- Open or shorted wiring in phase V 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
- Transmission warning message 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 or corrosion.
Step 3: Measure resistance between phase V and other phases at the pump connector; compare to specifications.
Step 4: Test pump motor operation by applying battery voltage directly (if safe) and monitor current draw.
Step 5: If wiring and motor check out, test PCM output signals for phase V.
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 low pump current can cause transmission overheating and damage. Have it diagnosed promptly.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, including parts (pump motor) and labor. Diagnostic fees may be additional.