What it means
The control module detects a low electrical level in the pressure control solenoid B control circuit. This indicates an electrical circuit fault; it does not by itself confirm a short to ground.
At a glance
- Usually lights the check-engine light
How it works
Pressure control solenoid B is an electrically operated valve that helps regulate hydraulic pressure in the transmission. The control module monitors the electrical level in solenoid B’s control circuit and sets P0966 when it detects a level below its expected range. This indicates an electrical fault but does not by itself confirm a short to ground.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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
- Record freeze-frame data and check transmission live data for when the fault occurs and whether solenoid B is being commanded.
- Inspect solenoid B’s connector and wiring for corrosion, damaged insulation, chafing, or loose pins.
- With the circuit safely isolated as specified by the manufacturer, check for an unintended connection between solenoid B’s control wire and ground.
- Check connector pin fit and circuit continuity, and measure solenoid B coil resistance against the manufacturer’s specification.
- If the solenoid and wiring pass, test the control module’s solenoid B driver and connections using the manufacturer’s procedure.
Common fixes
- Clean and secure corroded or loose solenoid B connector terminals.
- Repair chafed or damaged solenoid B control wiring and restore its insulation.
- Replace pressure control solenoid B if its coil or internal operation fails testing.
- Repair the control module connection or driver only if circuit testing confirms a module fault.
Can I keep driving?
Avoid towing and hard acceleration if shifts are harsh, delayed, slipping, or the transmission enters limp mode; abnormal pressure control can worsen wear. If it cannot shift predictably, stop in a safe place and arrange assistance.
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.