P2784: Input/Turbine Speed Sensor Correlation
The P2784 code indicates that the powertrain control module (PCM) has detected a correlation error between the input shaft speed sensor (turbine speed sensor) and the output shaft speed sensor. This typically means the transmission is slipping or the sensors are providing inconsistent data, which can lead to harsh shifting, delayed engagement, or transmission damage.
1. Most Common Causes
- Faulty input/turbine speed sensor 'A' or 'B'
- Wiring or connector issues in the sensor circuit
- Excessive torque converter slip
- Internal transmission mechanical wear (clutches, bands)
- Transmission control module (TCM) failure
- Speed differences due to transmission oil pump failure or low fluid level
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission slipping or harsh shifting
- Delayed engagement when shifting into gear
- Transmission overheating or unusual noises
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Check transmission fluid level and condition; top off or replace if necessary.
Step 3: Inspect wiring and connectors for the input/turbine speed sensor for damage or corrosion.
Step 4: Test the sensor resistance and signal output with a multimeter or oscilloscope.
Step 5: If sensor and wiring are okay, perform a transmission pressure test to check for internal mechanical issues.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with this code as it can cause further transmission damage. If the transmission is slipping severely, have the vehicle towed to a repair shop.
How much does it cost to fix?▼
The cost varies depending on the cause. Replacing a sensor typically costs $150-$400 including parts and labor. If internal transmission repairs are needed, costs can exceed $2,000.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.