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P27EC Buick Code - Transmission Range Control Valve 1 Position Switch Performance

Quick Answer

The P27EC code indicates a performance issue with the Transmission Range Control Valve 1 Position Switch. Common causes include Low transmission fluid levels, leading to inadequate hydraulic pressure, Faulty Transmission Range Control Valve 1 Position Switch, Transmission Range Control Valve 1 Position Switch harness is open or shorted. 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
P27EC Buick indicates Transmission Range Control Valve 1 Position Switch Performance.
Common causes
Common causes include Low transmission fluid levels, leading to inadequate hydraulic pressure, Faulty Transmission Range Control Valve 1 Position Switch, Transmission Range Control Valve 1 Position Switch harness is open or shorted.
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.
What is this?
Table of contents Created and updated by William Orellana on Oct 02, 2025
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Code P27EC Buick Description

The P27EC code indicates a performance issue with the Transmission Range Control Valve 1 Position Switch. This switch plays a critical role in the operation of the automatic transmission by providing the transmission control module (TCM) with information regarding the position of the transmission range. As the vehicle accelerates, the TCM relies on input signals from various sensors, including the automatic transmission input and output speed sensors, throttle position sensor, and others, to determine the optimal timing for shifting gears. When the TCM detects that the signals from the Transmission Range Control Valve 1 Position Switch are outside of the expected range, it triggers the P27EC code.
OBDII Code P27EC Buick - Transmission Range Control Valve 1 Position Switch Performance
P27EC Buick Code - Transmission Range Control Valve 1 Position Switch Performance

Common Causes of P27EC Buick

  1. Low transmission fluid levels, leading to inadequate hydraulic pressure
  2. Faulty Transmission Range Control Valve 1 Position Switch
  3. Transmission Range Control Valve 1 Position Switch harness is open or shorted
  4. Poor electrical connection in the Transmission Range Control Valve 1 Position Switch circuit
  5. Faulty Control Valve Solenoid Body affecting transmission operation

Symptoms of P27EC Buick

  1. Engine Light ON (or Service Engine Soon Warning Light)
  2. Erratic or harsh shifting between gears
  3. Delayed engagement when shifting from park to drive or reverse
  4. Increased engine RPM without corresponding vehicle acceleration
  5. Transmission overheating due to improper fluid flow

How to Fix P27EC Buick

  1. Perform a thorough inspection of the transmission fluid level and condition; top off or replace fluid as necessary.
  2. Test the Transmission Range Control Valve 1 Position Switch for proper operation and replace if faulty.
  3. Inspect the wiring harness and connectors associated with the Transmission Range Control Valve 1 Position Switch for any signs of damage or corrosion.
  4. Check the Control Valve Solenoid Body for functionality and replace if it is found to be defective.
  5. Clear the diagnostic trouble codes and perform a road test to ensure the issue has been resolved.

Cost to Fix P27EC Buick

The cost to diagnose and repair the P27EC code can vary significantly based on the specific issue and the vehicle make and model. Typical parts and labor costs can range from $150 to $600, depending on whether the Transmission Range Control Valve 1 Position Switch needs replacement or if there are additional issues such as wiring problems or solenoid failures. Labor rates generally range from $80 to $150 per hour, with dealerships often charging more than independent shops. It's advisable to get a detailed estimate based on your location and vehicle specifics.

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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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