LSIS (Left Side Impact Sensor) – Function, Symptoms, Location, Diagnosis, and Possible DTCs

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LSIS (Left Side Impact Sensor) – Function, Symptoms, Location, Diagnosis, and Possible DTCs

The LSIS (Left Side Impact Sensor) is an important component of the Supplemental Restraint System (SRS). It detects impacts on the left side of the vehicle and sends crash data to the Airbag Control Module (ACM), which determines whether to deploy the side airbags and seat belt pretensioners.

What Does LSIS Stand For?

LSIS = Left Side Impact Sensor

Main Functions

  • Detects left-side collisions.
  • Sends impact data to the Airbag Control Module.
  • Supports side airbag deployment decisions.
  • Works with front impact and rollover sensors.

Common Symptoms

  • Airbag warning light ON.
  • SRS diagnostic trouble codes stored.
  • Left side airbag disabled.
  • Sensor communication or circuit faults.

Typical Location

The LSIS is commonly installed inside the left B-pillar, left front door, left rear door, or lower side body. The exact mounting location varies by vehicle manufacturer and model.

Simple Signal Diagram

 Left Side Impact
        │
        ▼
+------------------+
|       LSIS       |
+------------------+
        │ Signal
        ▼
+------------------+
| Airbag Control   |
| Module (ACM)     |
+------------------+
        │
        ▼
 Left Side Airbag
 Pretensioner

Possible Diagnostic Trouble Codes (DTCs)

  • B0090 – Left Side Impact Sensor
  • B0091 – Left Side Impact Sensor Circuit
  • B1620 – Side Impact Sensor Circuit Fault
  • B1621 – Side Impact Sensor Signal Fault
  • B1630 – Left Side Impact Sensor Fault
  • Manufacturer-specific SRS communication codes

Diagnosis Tips

  • Read SRS codes using a compatible scan tool.
  • Inspect the LSIS connector for moisture, corrosion, or loose terminals.
  • Check wiring continuity between the LSIS and ACM.
  • Replace the sensor if internal failure is confirmed.

Important Note

Sensor location, wiring, connector pinout, and DTC definitions vary among vehicle manufacturers. Always consult the factory service manual before testing or replacing the LSIS.

Related SRS Components

  • RSIS – Right Side Impact Sensor
  • FIS – Front Impact Sensor
  • RFIS – Right Front Impact Sensor
  • LFIS – Left Front Impact Sensor
  • ACM – Airbag Control Module

Frequently Asked Questions

Can a faulty LSIS turn on the airbag warning light?

Yes. A malfunctioning LSIS typically causes the SRS warning light to illuminate.

Can the LSIS be repaired?

Most manufacturers recommend replacing a faulty side impact sensor rather than repairing it.

Can I drive with a failed LSIS?

Yes, but the left-side airbag system may not operate correctly during a side collision.

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