AutoCodes – Generic – P18C4

P18C4 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 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 2,677

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

What does this mean?

What are the Possible Causes of the DTC P18C4?

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?

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 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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Information for Specific Makes

P18C4 Buick — Gear Position Sensor Circuit 1 Low Voltage
P18C4 Cadillac — Gear Position Sensor Circuit 1 Low Voltage
P18C4 Chevrolet — Gear Position Sensor Circuit 1 Low Voltage
P18C4 GMC — Gear Position Sensor Circuit 1 Low Voltage

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 Code

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

- Common symptoms include issues with shifting gears, rough shifting, and the transmission staying in one gear.

2. What can cause OBDII code P18C4 to trigger?

- The code P18C4 can be triggered by a faulty gear position sensor, damaged wiring or connectors related to the sensor, or a low voltage condition in the sensor circuit.

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

- To diagnose the issue, you can perform a visual inspection of the sensor, check the wiring and connectors for damage, and use a multimeter to test the voltage in the sensor circuit.

4. Can a faulty gear position sensor be repaired, or does it need to be replaced?

- In most cases, a faulty gear position sensor will need to be replaced rather than repaired to resolve OBDII code P18C4.

5. Are there any DIY repair tips for fixing OBDII code P18C4?

- DIY repair tips include checking and cleaning the connectors, ensuring proper wiring connections, and following the manufacturer's diagnostic and repair procedures.

6. Can OBDII code P18C4 cause damage to the transmission?

- If left unresolved, OBDII code P18C4 can potentially cause damage to the transmission due to incorrect gear selection and shifting issues.

7. Is it safe to continue driving with OBDII code P18C4 present?

- It is not recommended to continue driving with OBDII code P18C4 present, as it can lead to further transmission problems and potential safety risks.

8. How much does it typically cost to repair OBDII code P18C4?

- The cost of repairing OBDII code P18C4 can vary depending on the extent of the issue, but it may range from $100 to $300 for parts and labor.

9. Can resetting the OBDII code P18C4 fix the issue temporarily?

- Resetting the code may temporarily clear the warning light, but it will not fix the underlying issue causing OBDII code P18C4 to trigger.

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

- The repair time for OBDII code P18C4 can vary based on the exact cause and extent of the issue, but it typically takes a few hours to complete the repair.