P0B0B — Auxiliary Transmission Fluid Pump Motor Supply Voltage Circuit #

Note: The description of DTC P0B0B may vary depending on the vehicle manufacturer. Always refer to OEM-specific documentation for precise terminology.

• AUXILIARY Transmission Fluid Pump Motor Supply Voltage Circuit (General/SAE)
• Aux Pump Motor Voltage Circuit Malfunction (Toyota / Lexus)
• Auxiliary Transmission Oil Pump Motor Voltage Range/Performance (Honda / Acura)
• A/T Fluid Pump Motor Voltage Circuit (Nissan / Infiniti)

Summary of Code P0B0B #

Diagnostic Trouble Code P0B0B indicates that the Engine Control Module (ECM) or Transmission Control Module (TCM) has detected an abnormality in the supply voltage circuit for the auxiliary transmission fluid pump motor. This auxiliary pump is often used in hybrid and some automatic transmissions to maintain fluid pressure when the main pump is not operating, such as during engine stop/start events. A disruption in the supply voltage can compromise the auxiliary pump’s ability to ensure proper lubrication and hydraulic pressure, potentially leading to shifting issues or even transmission damage if left unresolved. This code is typically triggered by an electrical problem—such as an open circuit, short, or voltage out of range—within the supply wiring or the pump motor itself.

Frequent Symptoms for Code P0B0B #

When code P0B0B appears, drivers and technicians may notice several symptoms. These can range from subtle irregularities in transmission performance to more pronounced warning lights or drivability issues. In some cases, the problem may only be detected during specific driving conditions, such as low-speed operation or when the engine switches off in hybrid vehicles.

• Check Engine Light (CEL) illuminated
• Transmission warning light or message
• Delayed or harsh gear shifts
• Transmission stuck in one gear (fail-safe/limp mode)
• Unusual noises from the transmission area
• Reduced fuel efficiency (in hybrid vehicles)

Most Probable Causes for Code P0B0B #

The causes of P0B0B are typically electrical in nature and often trace back to the components or wiring that supply power to the auxiliary transmission fluid pump. Identifying the root cause requires a systematic approach, as multiple factors can contribute to this issue.

1. Faulty auxiliary transmission fluid pump motor (internal electrical failure)
2. Open or shorted wiring harness (damaged, corroded, or disconnected wiring)
3. Blown fuse or faulty relay controlling the pump circuit
4. Poor electrical connection at the pump, relay, or control module
5. Defective Transmission Control Module (TCM) or Engine Control Module (ECM) (rare)

Step-by-Step Diagnosis for Code P0B0B #

Resolving code P0B0B requires a methodical diagnostic process. Eliminating obvious issues first can save time and prevent unnecessary parts replacement. Always follow OEM procedures and safety precautions when working on the transmission electrical system.

• 1. Verify the code with a scan tool and check for additional transmission or hybrid system codes.
• 2. Visually inspect the auxiliary transmission fluid pump and related wiring for signs of damage, corrosion, or loose connections.
• 3. Check the fuse and relay associated with the auxiliary pump circuit using a multimeter.
• 4. Test the supply voltage at the pump connector while the pump should be active. Compare readings to OEM specifications.
• 5. Perform a continuity and resistance check of the wiring harness between the control module, relay, and pump motor.
• 6. If available, use a bi-directional scan tool to command the auxiliary pump on/off and monitor response.
• 7. If all wiring and power supply checks out, test or replace the auxiliary transmission fluid pump motor as per OEM guidelines.
• 8. If the problem persists, suspect a faulty control module and follow manufacturer testing procedures.

Possible Repairs for Code P0B0B #

Once the root cause of P0B0B is identified, targeted repairs can restore normal operation. Addressing the underlying electrical fault is key to preventing repeat occurrences and further transmission issues.

• Replace the auxiliary transmission fluid pump motor if found faulty
• Repair or replace damaged wiring or connectors in the supply voltage circuit
• Replace blown fuse or faulty relay associated with the pump circuit
• Clean and secure all electrical connections to ensure proper contact
• Replace or reprogram the TCM/ECM only if conclusively diagnosed as faulty

Is It Safe to Drive with Code P0B0B? #

Driving with code P0B0B is NOT recommended. The auxiliary transmission fluid pump plays a crucial role in maintaining hydraulic pressure, especially in certain driving conditions or hybrid operation. If the pump fails to operate, you risk inadequate transmission lubrication and potential internal damage. In some vehicles, you may experience limp mode or harsh shifting, which can further compromise drivability. It’s best to have the issue diagnosed and repaired promptly to avoid costly repairs.

Vehicles Most Commonly Affected by Code P0B0B #

Code P0B0B is most often found in vehicles equipped with automatic transmissions that use an auxiliary fluid pump—particularly hybrids and certain late-model vehicles from specific manufacturers. While it can appear in a variety of makes, it is seen more frequently in:

• Toyota / Lexus hybrids (e.g., Prius, Camry Hybrid, RX Hybrid)
• Honda / Acura hybrids
• Nissan / Infiniti hybrid models
• Some GM and Ford hybrid or advanced automatic transmissions

Common Mistakes & Best Practices for Code P0B0B #

Misdiagnosing P0B0B can lead to unnecessary repairs and prolonged downtime. Following best diagnostic practices and avoiding common errors will ensure a more efficient and cost-effective fix.

• Replacing the auxiliary pump without checking wiring or relays
• Overlooking blown fuses or corroded connectors
• Ignoring OEM wiring diagrams and not using service information
• Not testing the pump circuit under actual operating conditions
• Clearing the code without addressing the root cause

Quick FAQ for Code P0B0B #

Here are some fast answers to common questions about code P0B0B:

• Q: Is P0B0B always caused by a bad auxiliary pump?
  A: Not always. While a faulty pump is common, wiring issues, blown fuses, or relay faults can also trigger this code. Always perform a thorough diagnosis before replacing parts.
• Q: Can I reset the code and keep driving?
  A: Clearing the code without fixing the problem may temporarily remove the warning, but the underlying fault will persist and could cause more serious transmission damage over time.
• Q: Will my car go into limp mode?
  A: Many vehicles will engage a fail-safe or limp mode when this code is detected, resulting in limited shifting capability and reduced performance to protect the transmission.