What computer diagnostics
reveal (and what they don't)

"Plug it into the tester and let's see" is a phrase heard often. Diagnostics help a lot, but they have limits. Here's what they can and can't reveal.

What the tester reads

The car's computers store errors: sensors reporting odd values, misfires, emissions issues. The tester brings them to light, with a code and a description.

Why the code isn't the final diagnosis

A code that says "lambda sensor" doesn't always mean the sensor is faulty. It could be a cracked hose or a bad contact. That's where the human work begins, not the machine's.

The tester shows you where to look. It doesn't always tell you what to change.

When it's worth doing

At any dashboard light, a higher fuel consumption or a misfire. It's cheap and it saves you from swapping parts on a guess.