P2784 OBD-II Trouble Code: Input/Turbine Speed Sensor A/B Correlation

check engine light

P2784 code definition

The P2784 code identifies an issue with the input signal from the turbine speed sensor to the PCM.

What the P2784 code means

The P2784 code is an indication that the engine turbine speed sensor is sending an input signal to your PCM (powertrain control module) that is incorrect. The majority of PCMs have been programmed to expect a gradual increase in input speed. After enough of an increase, the transmission will shift up in gear. When that increase is erratic or unusual, the PCM cannot effectively identify a proper shift point, and the P2784 code will be indicated.

What causes the P2784 code?

The incorrect turbine speed code may have several causes:

  • Incorrect or unusual input speed signals are most often caused by defective turbine speed sensors (either input or output)

  • corroding or damaged wiring

  • defective shift solenoids

  • defective engine temperature sensors

  • dirty, mixed, or otherwise incorrect transmission fluid

  • failure with the PCM is a much rarer cause

What are the symptoms of the P2784 code?

The most common symptoms of the P2784 code include issues with or failure of shifting, poorly operating speedometers, and engine stalling upon breaking or bringing the vehicle to a full stop. Less common symptoms of this code also include decreased fuel economy, misfiring of the engine, and occasionally an illuminated Check Engine Light.

How does a mechanic diagnose the P2784 code?

A P2784 code can be diagnosed by a qualified mechanic technician using a code reader, such as a OBD-II scanner. Before checking the vehicle’s turbine speed sensor, a mechanic should first identify any damaged or corroded wiring in the engine bay and replace before further investigation.

A mechanic should then locate the speed sensor, which can be found either in the transmission housing or mounted to the housing exterior depending on the vehicle’s make and model, and check for any visible damage. Then, all OBD-II codes should be cleared and a test drive should be performed, after which a qualified mechanic will check to see if the P2784 code reappeared.

Common mistakes when diagnosing the P2784 code

Properly diagnosing the P2784 code can be difficult. Symptoms of the P2784 code are often mistaken for…

  • Full vehicle speed malfunction
  • Transmission malfunction
  • Driveline malfunction
  • Engine misfire

These misdiagnoses have been reported to lead to unnecessary turbine speed sensor replacement.

How serious is the P2784 code?

If the symptoms of the P2784 code in the vehicle include engine stalling or shifting malfunctions, the vehicle is potentially not safe to drive and therefore should be diagnosed by a qualified mechanic as soon as possible. Since symptoms of this code also include a decrease in fuel economy, it’s best to have the vehicle looked at by a technician as soon as possible regardless of the noticeable symptoms.

What repairs can fix the P2784 code?

Once the vehicle is examined and diagnosed by a qualified mechanic, replacement parts for your vehicle may be necessary. The most common potential repairs to fix the P2784 engine trouble code include:

  • Wiring replacement
  • Turbine speed sensor replacement
  • Turbine speed sensor connector replacement

Additional comments for consideration regarding the P2784 code

Since the P2784 code has a number of possible causes, the problem should be thoroughly investigated and properly diagnosed before any parts are repaired or replaced.

Need help with a P2784 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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