AutoCodes – Chevrolet – P18C4 Chevrolet

P18C4 Chevrolet Code - Gear Position Sensor Circuit 1 Low Voltage

Quick Answer

The gear position sensor is a switching transistor mounted to the top of the transmission extension housing. Common causes include Faulty Gear Position Sensor, Gear Position Sensor harness is open or shorted, Gear Position Sensor circuit poor electrical connection. 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: P18C4 Chevrolet indicates Gear Position Sensor Circuit 1 Low Voltage.
Common causes: Common causes include Faulty Gear Position Sensor, Gear Position Sensor harness is open or shorted, Gear Position Sensor circuit poor electrical connection.
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 1,405

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 Feb 05, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P18C4 Chevrolet Description

The gear position sensor is a switching transistor mounted to the top of the transmission extension housing. The four wire sensor interfaces directly with the Engine Control Module (ECM). The ECM supplies 5 V to the gear position sensor on a 5 V reference circuit and also provides a ground path on a low reference circuit. The sensor provides a Pulse Width Modulated (PWM) duty cycle to the ECM on two signal circuits that is proportional to the linear and radial position of the corresponding magnet assembly mounted to the shift shaft. The vehicle uses the gear position sensor information primarily for Active Rev Matching and Active Fuel Management. The ECM monitors the radial position signal 1 circuit for low and high voltage conditions.

OBDII Code P18C4 Chevrolet - Gear Position Sensor Circuit 1 Low Voltage - AutoCodes.com — P18C4 Chevrolet Code - Gear Position Sensor Circuit 1 Low Voltage

What does this mean?

What are the Possible Causes of the DTC P18C4 Chevrolet?

Faulty Gear Position Sensor
Gear Position Sensor harness is open or shorted
Gear Position Sensor circuit poor electrical connection

How to Fix the DTC P18C4 Chevrolet?

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 P18C4 Chevrolet 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.

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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.

Frequently Asked Questions about P18C4 Chevrolet Code

What does the OBDII code P18C4 mean for my Chevrolet?

The code P18C4 indicates a low voltage condition in the gear position sensor circuit 1, which is responsible for detecting the current gear position of the transmission.

What are the common symptoms of the P18C4 code?

Common symptoms include erratic shifting, inability to shift gears, transmission warning lights on the dashboard, and poor acceleration.

What can cause the P18C4 code to trigger?

Causes can include a faulty gear position sensor, damaged wiring or connectors in the sensor circuit, low battery voltage, or issues within the transmission control module.

Is it safe to drive with the P18C4 code?

While it may still be possible to drive, it is not recommended as it can lead to transmission performance issues and potential further damage.

How can I diagnose the P18C4 code?

To diagnose the P18C4 code, start with a visual inspection of the wiring and connectors for damage, then use a multimeter to check the voltage at the gear position sensor. Additionally, scan for other related trouble codes.

What are some common repairs for the P18C4 code?

Common repairs include replacing the faulty gear position sensor, repairing or replacing damaged wiring or connectors, and resetting the transmission control module.

Can I reset the P18C4 code myself?

Yes, you can reset the code using an OBDII scanner, but this will not fix the underlying issue. It's important to address the cause of the code to prevent it from returning.

How much does it typically cost to fix the P18C4 issue?

Repair costs can vary widely depending on the cause, ranging from $100 for wiring repairs to over $300 for sensor replacement, plus labor costs.

Will clearing the P18C4 code fix my transmission issue?

Clearing the code may temporarily turn off the warning light, but it will not fix the underlying problem. If the issue persists, the code will likely return.