AutoCodes – Generic – P18AB

P18AB Code - Transmission Range Control Valve 1 Position Switch Circuit Stuck Off

Quick Answer

As the vehicle speed increases, the transmission control module (TCM) receives input signals from the automatic transmission input and output speed sensors, throttle position sensor and other vehicle sensors to determine the precise moment to de-energize or “turn off” 1-2-3-4-5-6 solenoid and the solenoid. Common causes include Low transmission fluid, 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: P18AB indicates Transmission Range Control Valve 1 Position Switch Circuit Stuck Off.
Common causes: Common causes include Low transmission fluid, 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.

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Code Popularity 981

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Oct 02, 2025

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P18AB Description

OBDII Code P18AB - Transmission Range Control Valve 1 Position Switch Circuit Stuck Off - AutoCodes.com — P18AB Code - Transmission Range Control Valve 1 Position Switch Circuit Stuck Off

What does this mean?

What are the Possible Causes of the DTC P18AB?

Low transmission fluid
Faulty Transmission Range Control Valve 1 Position Switch
Transmission Range Control Valve 1 Position Switch harness is open or shorted
Transmission Range Control Valve 1 Position Switch circuit poor electrical connection
Faulty Control Valve Solenoid Body

How to Fix the DTC P18AB?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P18AB code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P18AB code?

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Information for Specific Makes

P18AB Buick — Transmission Range Control Valve 1 Position Switch Circuit Stuck Off
P18AB Cadillac — Transmission Range Control Valve 1 Position Switch Circuit Stuck Off
P18AB Chevrolet — Transmission Range Control Valve 1 Position Switch Circuit Stuck Off
P18AB GMC — Transmission Range Control Valve 1 Position Switch Circuit Stuck Off

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.