What it means
Voltage on the second auxiliary transmission fluid pump control line is below the expected window. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
Auxiliary pump B's control circuit carries the TCM's command to operate the second transmission fluid pump, and the TCM monitors the circuit voltage. This code sets when that voltage falls below the expected range, which can result from a short to ground, a shorted motor winding, or high resistance at the connector.
Common causes
Most likely first.
- Control wire shorted to ground
- Motor winding short
- Connector pins corroded - high contact resistance
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
- Capture freeze-frame data and check live pump B command and circuit data to learn whether the low reading occurs during a command or at all times.
- Inspect pump B's wiring and connector for chafing to ground, water ingress, pushed-back pins, or corrosion.
- While monitoring the active fault, gently move the pump B harness and connector to check for an intermittent voltage change.
- Measure the control-circuit voltage and check for an unintended path to ground, comparing results with the manufacturer's specification.
- Test pump B's motor winding and connector contact resistance to separate a shorted motor from a wiring or terminal fault.
Common fixes
- Repair pump B's control wire where it is shorted to ground.
- Clean or replace corroded pump B connector terminals and restore proper pin contact.
- Repair harness damage that allows water in or causes the low reading during movement.
- Replace pump B if its winding is shorted.
Can I keep driving?
Avoid driving if the transmission slips, shudders, or shifts harshly or late, as the low pump B circuit reading may accompany loss of hydraulic support. If shifting remains normal, limit driving and get the circuit checked soon.
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.