P2784
Input/Turbine Speed Sensor A/B Correlation
Transmission
Generic OBD-II
Medium
What it means
P2784 sets when the transmission's two input/turbine speed sensors report speeds that don't agree. The TCM relies on these to time shifts and lockup, so a mismatch can trigger harsh or erratic shifting and often a limp-mode fallback. It usually points to a failing sensor or its wiring rather than internal transmission damage.
Medium
Can I keep driving? Short-term yes, but expect harsh or erratic shifting or limp mode — get it looked at soon to avoid driving in the wrong gear.
Common symptoms
What you'll notice
- Check-engine light on
- Harsh, delayed, or erratic shifts
- Transmission drops into limp/failsafe mode (limited gears)
- Speedometer or shift timing behaving inconsistently
Common causes
Most likely first
- One of the two input/turbine speed sensors failing or reading intermittentlyLikely
- Open, shorted, or chafed wiring between a sensor and the TCMCommon
- Poor or corroded connector at a speed sensorCommon
- Metal debris on a sensor tip or excessive rotor runoutLess often
- Faulty transmission control module (least likely)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and compare the two speed-sensor readings live — the one that drops out or disagrees is the suspect.
- Inspect both sensor connectors and wiring for corrosion, chafing, or loose pins.
- Check the suspect sensor's resistance/air gap and inspect the tip for metal debris; replace if out of spec.
- Confirm fluid level and condition, since low or aerated fluid can disturb sensor readings.
- Clear the code and road-test to verify both signals now track together.
FAQ
Quick answers
Is it safe to drive with P2784?+
For a short trip usually yes, but the transmission may shift harshly or enter limp mode. Drive gently and get it diagnosed before long trips.
Can I just clear P2784?+
It will return once the two sensors disagree again. Find and fix the failing sensor or wiring first.
Related codes
Often seen with P2784
Read & clear P2784 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX