What Does P0B0A Mean?
The powertrain control module has detected that the supply voltage to the auxiliary transmission fluid pump motor is below the minimum operating threshold. Low supply voltage will cause the pump motor to run slower than commanded, reducing fluid flow and pressure. The pump controller may also be unable to properly commutate the motor phases, causing erratic or stalled pump operation.
Common Causes
30%
High-resistance connection in the supply voltage wiring (corroded terminal or splice)
25%
Weak or discharged vehicle battery unable to maintain voltage under pump load
20%
Failing alternator or DC-DC converter not maintaining adequate system voltage
15%
Excessive voltage drop in the ground circuit for the pump controller
10%
Undersized or damaged supply wire reducing current-carrying capacity
Diagnostic Steps
1
Measure supply voltage at the pump control module connector pins with the pump operating. Compare with battery terminal voltage — the difference should not exceed 0.5V.
2
Test the vehicle battery with a load tester or conductance tester. A weak battery may drop voltage excessively when the pump motor demands current. Replace if CCA is below 70% of rated capacity.
3
Measure voltage drop across each connection point in the supply circuit (fuse holder, relay contacts, connector pins) while the pump is running. Any single point exceeding 0.2V drop needs cleaning or replacement.
4
Check the ground circuit voltage drop from the pump controller ground pin to the battery negative terminal. Should be less than 0.3V under load. Clean and retorque the ground connection if excessive.
5
Verify the charging system output. With the engine running, battery voltage should be 13.5-14.8V. Low charging voltage will cause this code, especially when multiple electrical loads are active.
Estimated Repair Cost
$50 - $800
Parts + labor, varies by vehicle and location
The powertrain control module has detected that the supply voltage to the auxiliary transmission fluid pump motor is below the minimum operating threshold. Low supply voltage will cause the pump motor to run slower than commanded, reducing fluid flow and pressure. The pump controller may also be una...
The most common cause of P0B0A (Auxiliary Transmission Fluid Pump Motor Supply Voltage Circuit Low) is: High-resistance connection in the supply voltage wiring (corroded terminal or splice)
Typical repair costs for P0B0A range from $50 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Low supply voltage reduces pump performance but does not typically create an immediate safety hazard. The vehicle will limit hybrid features as a precaution. If the low voltage is caused by a failing battery or charging system, other vehicle systems may also be affected. Address the root cause promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B0A to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid Transmission Auxiliary Systems
Difficulty
Type
Generic (SAE)
Recommended Tools
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