AutoCodes – Mercury – C109E Mercury

C109E Mercury Code - Vacuum Sensor Circuit Fault

Quick Answer

The vacuum sensor is used by the Anti-Lock Brake System (ABS) Module to determine if hydraulic pump intervention is necessary due to loss of vacuum in the booster. Common causes include Loose Brake Booster Vacuum Hose, Faulty Brake Booster Vacuum Sensor, Brake Booster Vacuum Sensor 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: C109E Mercury indicates Vacuum Sensor Circuit Fault.
Common causes: Common causes include Loose Brake Booster Vacuum Hose, Faulty Brake Booster Vacuum Sensor, Brake Booster Vacuum Sensor 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 881

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 Aug 12, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code C109E Mercury Description

The vacuum sensor is used by the Anti-Lock Brake System (ABS) Module to determine if hydraulic pump intervention is necessary due to loss of vacuum in the booster. The ABS module sends a 5-volt reference voltage to the sensor, the sensor compares the pressure in the booster to the ambient air pressure in the engine compartment and sends a varying voltage back to the ABS module based on the difference between the pressures. Normally, the pressure in the booster is much lower than ambient air pressure. As the pressure in the booster gets higher (closer to matching ambient air pressure), the lower the voltage sent back to the ABS module becomes.
When the vacuum in the brake booster falls below a predetermined level, the ABS module will command the hydraulic pump motor to activate on the next (and any subsequent) brake pedal application to assist with vehicle braking. The ABS module will continue to use the pump motor for braking assist as long as the low vacuum condition exists.

OBDII Code C109E Mercury - Vacuum Sensor Circuit Fault - AutoCodes.com — C109E Mercury Code - Vacuum Sensor Circuit Fault

What does this mean?

What are the Possible Causes of the DTC C109E Mercury?

Loose Brake Booster Vacuum Hose
Faulty Brake Booster Vacuum Sensor
Brake Booster Vacuum Sensor harness is open or shorted
Brake Booster Vacuum Sensor circuit poor electrical connection

How to Fix the DTC C109E Mercury?

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 C109E Mercury 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 C109E Mercury Code

1. What are the common symptoms of OBDII code C109E Mercury Vacuum Sensor Circuit Fault?

- Common symptoms include rough idling, stalling, poor acceleration, and decreased fuel efficiency.

2. What are the possible causes of the C109E code indicating a Vacuum Sensor Circuit Fault in a Mercury vehicle?

- The code may be triggered by a faulty vacuum sensor, damaged wiring or connectors, vacuum leaks, or a problem with the engine control module.

3. How can I diagnose the Vacuum Sensor Circuit Fault related to code C109E in my Mercury?

- To diagnose the issue, you can use an OBDII scanner to retrieve the code, visually inspect the vacuum sensor and related components, and perform a vacuum leak test.

4. Can a Vacuum Sensor Circuit Fault cause serious damage to my Mercury vehicle?

- While the fault itself may not cause immediate serious damage, ignoring it can lead to poor engine performance and potentially more costly repairs in the future.

5. Is it safe to continue driving my Mercury with the C109E code for Vacuum Sensor Circuit Fault?

- It is not recommended to drive with the C109E code present, as it can affect the engine's performance and potentially lead to further issues.

6. How can I repair the Vacuum Sensor Circuit Fault in my Mercury to resolve the C109E code?

- Repairing the fault may involve replacing the vacuum sensor, repairing damaged wiring or connectors, fixing any vacuum leaks, or reprogramming the engine control module.

7. Can I reset the C109E code related to the Vacuum Sensor Circuit Fault in my Mercury without fixing the underlying issue?

- While you can clear the code with an OBDII scanner, it is essential to address the root cause of the fault to prevent it from reoccurring.

8. Are there any DIY tips for troubleshooting the Vacuum Sensor Circuit Fault in my Mercury?

- DIY tips include checking for visible damage to the sensor and wiring, inspecting vacuum hoses for leaks, and ensuring all connections are secure.

9. How long does it typically take to repair the Vacuum Sensor Circuit Fault triggering the C109E code in a Mercury?

- Repair times can vary depending on the exact cause of the fault, but it may take anywhere from 1 to 3 hours to diagnose and repair the issue.

10. Can a professional mechanic help me diagnose and repair the Vacuum Sensor Circuit Fault indicated by the C109E code in my Mercury?

- Yes, a qualified mechanic can use specialized tools and expertise to accurately diagnose and repair the Vacuum Sensor Circuit Fault in your Mercury vehicle.