AutoCodes – GMC – P18C4 GMC

P18C4 GMC 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 GMC 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 1,279

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 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 radial position signal 1 circuit for low and high voltage conditions.

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

What does this mean?

What are the Possible Causes of the DTC P18C4 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 P18C4 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 P18C4 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 P18C4 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 P18C4 GMC Code

1. What are the common symptoms of OBDII code P18C4 GMC (Gear Position Sensor Circuit 1 Low Voltage)?

- Common symptoms include erratic shifting behavior, difficulty shifting gears, and the transmission staying in one gear.

2. What are the possible causes of OBDII code P18C4 GMC?

- The code P18C4 GMC can be caused by a faulty gear position sensor, damaged wiring or connectors in the circuit, or a malfunctioning transmission control module.

3. How can I diagnose the cause of OBDII code P18C4 GMC?

- To diagnose the issue, you can use a scan tool to retrieve the specific fault code, visually inspect the wiring and connectors for any damage, and test the gear position sensor for proper operation.

4. Can I continue driving with OBDII code P18C4 GMC active?

- It is not recommended to continue driving with the P18C4 GMC code active, as it can lead to further damage to the transmission and affect the vehicle's drivability.

5. How can I repair OBDII code P18C4 GMC?

- Repairing the P18C4 GMC code may involve replacing the faulty gear position sensor, repairing or replacing damaged wiring or connectors, or reprogramming the transmission control module.

6. Is it possible to reset OBDII code P18C4 GMC without repairing the issue?

- While you can clear the code temporarily, it is important to address the underlying issue causing the P18C4 GMC code to prevent further transmission problems.

7. How much does it cost to repair OBDII code P18C4 GMC at a dealership or a repair shop?

- The cost of repairing the P18C4 GMC code can vary depending on the specific cause of the issue, but it may range from $200 to $500, including parts and labor.

8. Can a DIY enthusiast fix OBDII code P18C4 GMC at home?

- DIY enthusiasts with the necessary tools and knowledge of automotive systems may be able to diagnose and repair the P18C4 GMC code at home, but it is recommended to seek professional help if unsure.

9. Are there any preventative measures to avoid OBDII code P18C4 GMC in the future?

- Regular maintenance of the transmission system, including checking and replacing worn-out sensors or components, can help prevent the occurrence of OBDII code P18C4 GMC.

10. How long does it take to repair OBDII code P18C4 GMC?

- The repair time for OBDII code P18C4 GMC can vary based on the specific cause of the issue and the availability of parts, but it may take a few hours to a full day for the repair to be completed.