What it means
The supply voltage circuit of auxiliary transmission fluid pump A motor reports a open condition.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Auxiliary transmission-fluid pump A needs a supply-voltage feed to run its motor and maintain hydraulic pressure. P0B09 is set when the module detects an open condition in that feed, so pump A may not receive power and transmission operation may be restricted.
Common causes
Most likely first.
- Open in supply wire
- Supply fuse blown
- Pin pushed back out of connector body
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Save freeze-frame data and check for pump A, transmission-pressure, and supply-circuit codes to learn when the open was detected.
- Use scan-tool data or commanded pump status, if available, to confirm whether pump A is being requested but not operating.
- Inspect the pump A supply fuse and related wiring for a blown fuse, damaged insulation, loose connector, or a terminal pushed back in the connector body.
- With the circuit de-energized as required by service information, test the supply path for continuity from its source to pump A and check connector contact condition.
- If the supply path is intact, verify voltage at the pump A feed during the specified commanded test and trace any interruption toward the supply or control source.
Common fixes
- Reconnect a pushed-back or loose pump A supply terminal.
- Repair an open or damaged section of the supply wire.
- Replace a failed fuse after checking for the cause of the open or overload.
- Repair the supply source or control connection if it fails the specified circuit test.
Can I keep driving?
A failed pump A feed can cause delayed, harsh, or missing shifts and limp mode, so avoid driving in traffic or on a long route if shifts are abnormal. Stop safely if the transmission slips or loses drive, since continued operation can damage the transmission.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.