Engine-CodesChevrolet – P1783 2020 Chevrolet Silverado

P1783 2020 Chevrolet Silverado Code - Input Speed Sensor Direction Not Plausible Forward

Quick Answer

The P1783 code indicates that the Input Speed Sensor (ISS) is reporting a direction that is not plausible for forward movement. Common causes include Faulty Transmission Input Speed Sensor, Open or shorted wiring in the Transmission Input Speed Sensor harness, Poor electrical connection in the Transmission Input Speed Sensor circuit. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P1783 2020 Chevrolet Silverado indicates Input Speed Sensor Direction Not Plausible Forward.
Common causes
Common causes include Faulty Transmission Input Speed Sensor, Open or shorted wiring in the Transmission Input Speed Sensor harness, Poor electrical connection in the Transmission Input Speed Sensor circuit.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Table of contents Created and updated by William Orellana on Jun 01, 2026
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Code P1783 2020 Chevrolet Silverado Description

The P1783 code indicates that the Input Speed Sensor (ISS) is reporting a direction that is not plausible for forward movement. The ISS plays a critical role in the operation of the transmission by detecting the speed of the primary pulley and sending this information to the Transmission Control Module (TCM). This sensor is vital for determining the appropriate shift patterns, line pressure, and overall transmission performance. When the ISS detects an inconsistency in the expected signal—specifically when the voltage exceeds 4.75 volts for a duration of 0.8 seconds—the TCM interprets this as a malfunction, triggering the P1783 code.

OBDII Code P1783 2020 Chevrolet Silverado - Input Speed Sensor Direction Not Plausible Forward
P1783 2020 Chevrolet Silverado Code - Input Speed Sensor Direction Not Plausible Forward

Common Causes of P1783 2020 Chevrolet Silverado

  1. Faulty Transmission Input Speed Sensor
  2. Open or shorted wiring in the Transmission Input Speed Sensor harness
  3. Poor electrical connection in the Transmission Input Speed Sensor circuit
  4. Malfunctioning Control Solenoid Valve Assembly
  5. Contaminated or damaged transmission fluid affecting sensor performance

Symptoms of P1783 2020 Chevrolet Silverado

  1. Engine Light ON (or Service Engine Soon Warning Light)
  2. Erratic or harsh shifting during acceleration
  3. Delayed engagement when shifting from park to drive or reverse
  4. Increased engine RPMs without corresponding vehicle speed
  5. Transmission overheating due to improper line pressure

How to Fix P1783 2020 Chevrolet Silverado

  1. Perform a visual inspection of the Input Speed Sensor and its wiring harness for damage or disconnections.
  2. Test the Input Speed Sensor using a multimeter to check for proper voltage and signal output.
  3. If the sensor is faulty, replace the Input Speed Sensor with a new one.
  4. Inspect and repair any damaged wiring or connectors in the sensor circuit.
  5. Clear the diagnostic codes and perform a road test to ensure proper transmission operation.

Cost to Fix P1783 2020 Chevrolet Silverado

The cost to diagnose and repair the P1783 code typically ranges from $150 to $600, depending on the specific issue identified. Replacing the Input Speed Sensor may cost between $100 and $300 for parts and labor, while more extensive repairs involving the control solenoid or wiring issues can increase the total cost. Labor rates vary widely, with most shops charging between $80 and $150 per hour. Dealerships may charge higher rates, while independent shops often offer more competitive pricing. Always consider the make and model of your vehicle, as well as local labor rates, when estimating repair costs.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

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