P2784

Code

Generic P — Powertrain

Input/Turbine Speed Sensor A/B Correlation

Brand: Generic

Type: P — Powertrain

Views: UK: 30 EN: 38 RU: 25

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty input/turbine speed sensor A or B
Damaged or shorted wiring or connector(s) to one or both sensors
Poor signal ground or reference voltage problem
Contaminated or damaged tone ring/reluctor wheel on turbine shaft
Intermittent connector contact (corrosion, broken pins)
Failed transmission components causing unexpected turbine speed (e.g., slipping clutch, damaged gear)

Symptoms

Check Engine Light (MIL) illuminated and DTC P2784 stored
Erratic shift timing or harsh/late shifts
Transmission slips or loss of proper engagement
Inaccurate or fluctuating input/turbine speed readings on a scan tool
Reduced performance or limp-in mode in some vehicles
Intermittent faults that may clear and return

What to check

Read and record freeze-frame and live data for turbine/input speed A and B with a scan tool
Check for additional transmission/engine DTCs that may be related
Visually inspect sensor connectors and wiring harness for damage, corrosion, or disconnection
Backprobe sensor connector(s) to verify reference voltage, ground, and signal while cranking and at idle
Measure sensor resistance and compare with manufacturer specification (if available)
Perform wiggle test on harness while monitoring live sensor signals to find intermittent faults

Signal parameters

Sensor types: Hall-effect (square wave, typically 0–5 V) or variable reluctor/VR (AC sine wave, typically 0.2–2 VAC at idle, increasing with rpm)
Reference voltage (Hall sensors): commonly 5 V (verify vehicle spec)
Signal frequency: proportional to rotational speed; both A and B should track proportionally to engine/transmission input RPM
Expected correlation: A and B signals should show consistent frequency and phase relationship appropriate to sensor placement; large differences, missing pulses, or intermittent gaps are abnormal
Typical resistance (VR sensors): varies by make — often 500–1500 ohms; check service data for exact value

Diagnostic algorithm

Retrieve freeze-frame data and all related DTCs. Note conditions when code set (speed, engine load, gear).
With ignition on, inspect connectors at both input/turbine sensors for corrosion, bent/broken pins, or moisture. Repair/clean as needed.
Backprobe connector(s): verify sensor reference voltage (Hall) and ground. If reference or ground missing, trace and repair power/ground circuits.
Measure sensor resistance (with connector disconnected) and compare to spec. Replace sensor if out of range.
Use a scan tool to monitor Input/Turbine Speed A and B simultaneously while cranking and during a road test. Note differences, dropouts, or spikes.
Use an oscilloscope to capture and compare waveforms from sensors A and B; look for missing pulses, low amplitude (VR), or excessive noise. Replace sensor if waveform is abnormal.
Perform wiggle test on harness/wiring while observing live data/waveform to find intermittent open/short. Repair or replace damaged wiring/harness.
Inspect tone ring/reluctor and surrounding area for damage, debris, or magnetic interference. Repair or replace damaged tone ring or related hardware.
If electrical and sensor checks are good but turbine speed is anomalous, investigate internal transmission faults (slipping clutch, damaged gears, torque converter problems).
After repairs, clear codes and perform test drive to confirm the fault does not return and that turbine/input speed A and B correlate normally.

Likely causes

Damaged wiring or connector to one of the speed sensors
Failed speed sensor (most common single component fault)
Tone ring damage or missing teeth causing inconsistent pulses
Intermittent connection or poor ground causing signal dropouts
Mechanical transmission slippage or torque converter issue producing unexpected turbine speed

Fault status

⚠️ Status

PCM detected poor correlation between Input/Turbine Speed Sensor A and B signals (P2784). This indicates inconsistent or mismatched speed readings that can affect transmission control. Inspect sensors, wiring, tone ring, and transmission operation.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours