Diagnosis
- How do I diagnose a check engine light?
Start by scanning for trouble codes with an OBD-II scanner. The code will point you to the affected system; then you can inspect components, test with a multimeter, and consult repair guides for your specific make and model. - What causes a misfire code?
A misfire code is caused by anything that prevents proper combustion in a cylinder: ignition problems (spark plugs, coils), fuel delivery issues (injectors, pump), or mechanical faults (low compression, valve problems). - Why is my car shaking at idle?
Shaking at idle is often caused by engine misfires, worn motor mounts, or a rough idle due to vacuum leaks or dirty fuel injectors. Diagnosing the exact cause requires checking for codes and inspecting components. - How do I test an oxygen sensor?
You can test an oxygen sensor with a scan tool or a digital multimeter. Look for a voltage that rapidly switches between about 0.1V and 0.9V on a good sensor. - What does a vacuum leak sound like?
A vacuum leak often sounds like a high-pitched whistle or hiss coming from the engine bay. It may be constant or change with engine speed. - Why does my car stall at stop signs?
Stalling at stop signs is usually caused by a dirty throttle body, a faulty idle air control valve, or a vacuum leak. It can also be due to ignition or fuel delivery problems.