Engine-Codes.com
Engine-Codes – Buick – P0B04 Buick

P0B04 Buick Code - Auxiliary Transmission Fluid Pump Low Current

Quick Answer

The Diagnostic Trouble Code (DTC) P0B04 indicates a low current issue with the auxiliary transmission fluid pump in hybrid and electric vehicles. Common causes include Faulty Transmission Fluid Pump Electric/AuxiliaryTransmission Fluid Pump Electric/Auxiliary harness is open or shortedTransmission Fluid Pump Electric/Auxiliary circuit poor electrical connectionFaulty Power Inverter ModuleWorn or damaged motor control module components. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0B04 Buick indicates Auxiliary Transmission Fluid Pump Low Current.
Common causes
Common causes include Faulty Transmission Fluid Pump Electric/AuxiliaryTransmission Fluid Pump Electric/Auxiliary harness is open or shortedTransmission Fluid Pump Electric/Auxiliary circuit poor electrical connectionFaulty Power Inverter ModuleWorn or damaged motor control module components.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Nov 05, 2025
💬 Need more help? Ask Auto Expert for instant answers — it's free!
AutoCodes App

Fix Your Car Smarter

Try the New AutoCodes App!

Get complete OBDII diagnostics, repair solutions, and cost estimates, plus AI chat support on demand.

AutoCodes App on Google Play

Code P0B04 Buick Description

The Diagnostic Trouble Code (DTC) P0B04 indicates a low current issue with the auxiliary transmission fluid pump in hybrid and electric vehicles. This pump is crucial for maintaining proper transmission fluid pressure, which is essential for smooth gear shifting and overall transmission performance. The power inverter module, which integrates the motor control modules and the hybrid/EV powertrain control module, manages the operation of this pump. The pump motor operates on three-phase AC electricity, with the motor stator coil configured in a wye formation. Each phase of the motor is monitored by current sensors that detect the electrical current flowing through them. When the current in any of these phases drops below 1 ampere, the DTC P0B04 is triggered.
OBDII Code P0B04 Buick - Auxiliary Transmission Fluid Pump Low Current
P0B04 Buick Code - Auxiliary Transmission Fluid Pump Low Current

Common Causes of P0B04 Buick

  1. Faulty Transmission Fluid Pump Electric/Auxiliary
  2. Transmission Fluid Pump Electric/Auxiliary harness is open or shorted
  3. Transmission Fluid Pump Electric/Auxiliary circuit poor electrical connection
  4. Faulty Power Inverter Module
  5. Worn or damaged motor control module components

Symptoms of P0B04 Buick

  1. Engine Light ON (or Service Engine Soon Warning Light)
  2. Erratic or harsh shifting during gear changes
  3. Decreased fuel efficiency
  4. Transmission overheating warnings
  5. Vehicle may enter limp mode, restricting power and speed

How to Fix P0B04 Buick

  1. Use a diagnostic scanner to confirm the P0B04 code and check for any additional codes.
  2. Inspect the wiring and connectors associated with the auxiliary transmission fluid pump for any signs of damage, corrosion, or loose connections.
  3. Test the auxiliary transmission fluid pump for proper operation and current draw; replace if faulty.
  4. Examine the power inverter module and motor control modules for any signs of failure or damage; replace as necessary.
  5. Clear the DTC and perform a road test to ensure that the issue has been resolved and that the vehicle operates normally.

Cost to Fix P0B04 Buick

The cost to diagnose and repair the P0B04 code can vary widely based on the specific issue and labor rates in your area. Typical parts for the auxiliary transmission fluid pump can range from $100 to $500, while labor costs may range from $80 to $150 per hour, depending on the shop's location and whether it's a dealership or independent shop. Overall, you might expect to spend between $300 and $1,200 for parts and labor combined, depending on the extent of the repairs needed.

Need more information about the P0B04 Buick code?

Need more information on how to fix the P0B04 Buick code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0B04 Buick code diagnosed by a professional: Find a repair shop in your area

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0B04 Buick Code

No Frequently Asked Questions about P0B04 Buick Code found.

Discuss the causes and fixes for P0B04 Buick OBDII Code

Submit a New Comment

Code P0B04 Buick comments

No comments found for this page.