Your car already told you which family the fault lives in — with the sound it made at the key. Three rounds of see/hear/smell questions place you on one of 12 branches, and every branch comes with what it proves, the free check, and the exact thing to refuse to buy.
Runs in your browser. Nothing is uploaded — your driveway, your dead car, your business.
Start with what you heardTwo people help here: one drives the key, one listens and watches the dash. This one question splits no-starts into three families.
Crank or no-crank, catch or no-catch, stays or dies — that single observation halves the fault list before anyone opens a manual. The tree follows the same first three moves every shop manual makes.
Every branch gives you a free check that means something, a list of parts to refuse to buy untested, and the exact question that exposes whether the next person who touches the car has actually tested anything.
Stuck or unsure, the branch writes itself into the booking form — your findings arrive with you, and the flat $150 mobile visit means the meter, not the parts cannon, is the next thing pointed at your car.
The fine print, honestly: this tree reads your observations, not your engine. A branch is a narrowing, never a diagnosis — live-data, meter, and scope work on the car is the only thing that names a failed part. Prices shown are rough ranges for planning, the same convention every knowledge page on this site uses.
Because most of the expensive no-start horror stories are tow-and-swap stories: the car gets dumped at a bay, and the diagnosis becomes a parts experiment in someone else's rush. The tree costs nothing, runs in your driveway with the tools you already have (ears, eyes, a nose), and hands every person you talk to a written-down branch and the right first question. If it ends up needing a meter, you will know exactly which meter — which is what makes the mobile visit flat-rate instead of open-ended.
Surprisingly load-bearing. No-crank vs. crank-no-start vs. start-then-stall is the SAME first split every factory service manual uses, and the follow-up questions are the same senses a tech uses at the car. The tree is honest about its ceiling: it names which FAMILY the fault lives in and what to refuse to buy; only a test on the car names a PART.
No — deliberately. Buying a part before a test names it is how a $15 relay becomes a $900 fuel-pump story, which is the exact pattern every page on this site documents. The tree tells you what your observation PROVES, the free check that narrows further, and the question that exposes whether a shop has actually tested.
No. The tree runs entirely in your browser — no server call, no stored answers, no analytics on what you pick. Close the tab and it never happened. People diagnosing in their driveway deserve a tool, not a lead form.
The Full Mobile Diagnostic is a flat $150 at your driveway, and the branch you found comes pre-filled on the booking form — the tech arrives knowing whether to bring a pressure gauge or a scope. If all you needed was the $6 terminal clean the tree walked you through, you paid nothing at all.