LFIS (Left Front Impact Sensor) – Function, Symptoms, Location, and Diagnosis

The LFIS (Left Front Impact Sensor) is a critical component of the Supplemental Restraint System (SRS). It monitors collision forces at the left front of the vehicle and sends impact information to the Airbag Control Module (ACM), which determines whether the airbags and seat belt pretensioners should deploy.

What Does LFIS Stand For?

LFIS = Left Front Impact Sensor

Main Functions

• Detects frontal impact on the left side.
• Sends crash data to the Airbag Control Module.
• Works together with the right front and side impact sensors.
• Helps determine airbag deployment timing.

Common Symptoms of a Faulty LFIS

• Airbag warning light stays ON.
• SRS fault codes stored in memory.
• Airbag system disabled.
• Communication or circuit faults related to the left front sensor.

Typical Location

The LFIS is commonly mounted behind the front bumper or on the left side of the radiator support. The exact position depends on the vehicle manufacturer and model.

Simple Signal Diagram

 Left Front Impact
        │
        ▼
+------------------+
|       LFIS       |
+------------------+
        │ Signal
        ▼
+------------------+
| Airbag Control   |
| Module (ACM)     |
+------------------+
        │
        ▼
 Airbags / Pretensioners

Diagnosis Tips

• Scan the SRS system for diagnostic trouble codes.
• Inspect the sensor connector for corrosion or loose terminals.
• Check wiring continuity between the LFIS and ACM.
• Replace the sensor if it fails manufacturer specifications.

Important Note

LFIS wiring, connector pinout, and operating values vary between vehicle manufacturers and models. Always consult the factory service manual before testing or replacing the sensor.

Related SRS Components

• RFIS – Right Front Impact Sensor
• ACM – Airbag Control Module
• Clock Spring
• Seat Belt Pretensioner
• Side Impact Sensor

Frequently Asked Questions

What does LFIS do?

It detects a left-front collision and sends impact data to the Airbag Control Module.

Can a faulty LFIS turn on the airbag warning light?

Yes. A defective LFIS commonly triggers the SRS warning light and stores diagnostic trouble codes.

Can LFIS be repaired?

Impact sensors are generally replaced rather than repaired after failure or collision damage.