Diagnose by Symptom

Use symptom-first diagnosis when you do not know the exact code yet. These pages connect what you feel in the car with likely OBD2 codes, repair actions, and scanner recommendations.

Symptom Cluster

Check Engine Light On

MIL illuminated with or without immediate drivability issues.

8 related codes

Symptom Cluster

Hard Start / No Start

Starting issues including extended cranking or complete no-start.

7 related codes

Symptom Cluster

Poor Fuel Economy

Noticeable MPG drop from rich/lean corrections or cold enrichment.

5 related codes

Symptom Cluster

Rough Idle

Idle vibrations, unstable RPM, and engine stumble when stopped.

4 related codes

Symptom Cluster

Power Loss

Weak acceleration, hesitation, and noticeable loss of engine output.

4 related codes

Symptom Cluster

ABS / Traction Warning

ABS, traction, ESC, or stability control warnings on dash.

3 related codes

Symptom Cluster

Airbag / SRS Warning

Airbag lamp or SRS system alert related to deployment circuits.

2 related codes

Symptom Cluster

High Idle

Warm idle speed remains above normal target RPM.

1 related code