AutoCodes – GMC – P18C9 GMC

P18C9 GMC Code - Gear Position Sensor Gear Ratio Not Plausible

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: P18C9 GMC indicates Gear Position Sensor Gear Ratio Not Plausible.
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 1,250

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 P18C9 GMC 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 sensor signal input for an incorrect neutral condition.

OBDII Code P18C9 GMC - Gear Position Sensor Gear Ratio Not Plausible - AutoCodes.com — P18C9 GMC Code - Gear Position Sensor Gear Ratio Not Plausible

What does this mean?

What are the Possible Causes of the DTC P18C9 GMC?

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

How to Fix the DTC P18C9 GMC?

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 P18C9 GMC 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 P18C9 GMC code?

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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 P18C9 GMC Code

1. What are the common symptoms of OBDII code P18C9 GMC (Gear Position Sensor Gear Ratio Not Plausible)?

- The common symptoms include erratic shifting behavior, transmission slipping, and the transmission may fail to engage properly.

2. What can cause the OBDII code P18C9 GMC to trigger?

- The code P18C9 GMC is triggered when the gear position sensor detects a gear ratio that is not within the expected range.

3. How serious is the OBDII code P18C9 GMC?

- The code P18C9 GMC is a serious issue as it can lead to transmission problems and affect the overall drivability of the vehicle.

4. How can I diagnose the OBDII code P18C9 GMC?

- Diagnosing the code P18C9 GMC typically involves using a scan tool to read the code and checking the gear position sensor for proper operation.

5. Can I still drive my vehicle with the OBDII code P18C9 GMC?

- It is not recommended to drive your vehicle with the code P18C9 GMC as it can lead to further damage to the transmission.

6. What are some repair tips for fixing the OBDII code P18C9 GMC?

- Repairing the code P18C9 GMC may involve replacing the gear position sensor, checking for wiring issues, or recalibrating the sensor.

7. How much does it cost to repair the OBDII code P18C9 GMC?

- The cost of repairing the code P18C9 GMC can vary depending on the extent of the issue and whether you do the repairs yourself or take it to a professional mechanic.

8. Can a DIY enthusiast fix the OBDII code P18C9 GMC?

- Some DIY enthusiasts may be able to fix the code P18C9 GMC if they have the necessary tools and knowledge of automotive repairs.

9. Is it common for the OBDII code P18C9 GMC to recur after repairs?

- If the underlying issue causing the code P18C9 GMC is not properly addressed, it is possible for the code to recur after repairs.

10. How can I prevent the OBDII code P18C9 GMC from occurring again in the future?

- Regular maintenance of the transmission system, including checking the gear position sensor and transmission fluid, can help prevent the code P18C9 GMC from occurring again.