What it means
The Brake Transmission Shift Interlock prevents shifting out of Park unless the brake pedal is pressed. The TCM compares the brake-pedal input to the BTSI solenoid command and detects an inconsistency — for example shift permitted while brake not pressed, or interlock active while brake is pressed.
At a glance
- Usually lights the check-engine light
How it works
The brake transmission shift interlock uses a brake-pedal signal and an interlock mechanism to keep the selector in Park until the brake is applied. The control module compares the brake input with the interlock command and sets P081F when the interlock state does not agree, such as when a stuck brake switch or misadjusted mechanism permits or blocks shifting at the wrong time.
Common causes
Most likely first.
- Stuck brake pedal switch
- Mis-adjusted BTSI mechanism
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 related brake-switch or transmission codes to see which interlock state was recorded.
- Observe scan-tool brake-pedal and interlock data while pressing and releasing the pedal, confirming the brake input changes consistently.
- Check the brake lamps for correct operation as a simple indication of whether the brake switch is responding.
- Inspect the BTSI mechanism and linkage for binding or misadjustment, and check the brake switch and interlock connectors for loose or damaged wiring.
- Test the brake switch, interlock solenoid, and their circuits against the wiring diagram and manufacturer's procedure.
Common fixes
- Adjust the BTSI mechanism to the manufacturer's specification.
- Replace a brake pedal switch that sticks or reports the wrong state.
- Repair loose, damaged, or corroded interlock wiring or connectors.
- Replace a failed interlock solenoid after confirming its circuit is sound.
Can I keep driving?
The selector may remain locked in Park or may be released when the brake is not pressed, creating a risk of unintended movement. Keep the parking brake applied, do not force the shifter, and have the interlock checked promptly.
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.