The B1378 OBD2 fault code relates to the Oil Level Lamp circuit. This lamp provides lighting for steps or running boards. When the circuit circuit failure, the lamp may fail to illuminate.

At AIscanAuto, we help drivers quickly identify OBD2 trouble codes, understand their root causes, and find the right fix.

Symptoms

• Running board lamp not working
• Possible bulb warning on dashboard
• Other related lamps also affected

Common Causes

• Burnt bulb — most common cause
• a general circuit failure is detected — can result from wiring faults, connector issues, or component failure
• Wiring issues — damaged harness
• Connector problems — corrosion

Step-by-Step Diagnosis

1. Scan with OBD2 tool — Confirm B1378.
2. Check bulb — Test with multimeter or swap.
3. Inspect wiring — Check for damage.
4. Test voltage at lamp — Verify power and ground.

Repair & Solutions

• Replace bulb if burnt.
• Repair wiring.
• Clean connectors.

Related Codes

• B1375 — Oil Change Reset Button Circuit Short To Ground
• B1376 — Oil Level Lamp Circuit Short To Battery
• B1377 — Oil Level Lamp Circuit Short To Ground

External References

- OBD2Pros — Complete DTC Reference

About This Guide

This diagnostic article is an original guide created by AIscanAuto for educational and troubleshooting purposes. The technical information about OBD2 DTC codes is based on publicly available automotive diagnostic standards and industry best practices. External links provided in the "External References" section are for additional reading and context only — they do not imply endorsement or ownership of third-party content. All repair procedures should be performed by qualified technicians.