How we research
Quick answer
Code definitions are the public SAE J2012 and ISO 15031-6 standards described in our own words. Causes are ordered cheapest and most common first, deliberately, because the component named in a code is usually the most expensive candidate rather than the most likely one. All 175 products come from verified live listings, so no price, image or product on this site was invented.
The code pages
Every one of the 273 code pages starts from the standardised generic definition in SAE J2012 and ISO 15031-6. Those definitions are a public standard, and they are described here in our own words rather than reproduced from any commercial trouble code database.
On top of the definition, each page carries fields that are editorial rather than standard: what the code means in plain language, the likely causes in order, what each one costs to ignore, whether the car is safe to drive, what to look at in freeze frame, and which capability tier of tool the diagnosis needs. Those are judgements, and they are made the same way on every page.
How causes are ordered
Cheapest and most common first, always. A loose fuel cap comes before a failed evaporative canister. A dirty mass air flow sensor comes before a failed one. A corroded ground comes before a failed control module. This ordering is deliberate and it is the opposite of how a code is usually read, because the component named in the code text is normally the most expensive candidate in the list.
The product catalog
Products are sourced by category from a live product API, and then filtered hard. A listing with no image is rejected, because a card with a broken image is worse than no card. A listing with no price is rejected, because the alternative is showing a figure nobody gave us. A listing whose price falls outside a sanity band for its category is rejected rather than clamped, because a price far outside the band nearly always means the result is not the product the query meant. Near-duplicate listings inside a category are collapsed to the cheaper one.
| Category | Products |
|---|---|
| scanner-bidi | 21 |
| scanner-pro | 20 |
| shop-chemical | 19 |
| scanner-live | 15 |
| dongle | 11 |
| obd1 | 10 |
| battery-tester | 8 |
| o2-socket | 8 |
| borescope | 7 |
| compression | 7 |
| injector-test | 7 |
| multimeter | 7 |
| reader-basic | 7 |
| fuel-pressure | 6 |
| gas-cap | 5 |
| test-leads | 5 |
| test-light | 5 |
| vacuum-test | 5 |
| smoke-machine | 2 |
| Total | 175 |
Capability flags
The chips on a product card, such as live data or bidirectional, are read from the listing title and only where the listing states the capability outright. A missing flag therefore means the listing does not claim it, never that the tool lacks it. That distinction matters enough that the selector tool is written to respect it rather than to treat absence as a negative.
The rules we do not break
- No invented ASIN, price or product image. If it cannot be verified, it is left out.
- No claim of in-person testing, anywhere, in any wording.
- No assertion about a specific reader's specific vehicle. Coverage and procedures vary by make and model year, and the pages say so.
- Where a tool has no honest answer, it refuses and explains why instead of producing a plausible number.
- Safety language is not softened. A code that means stop driving says stop driving.
Common questions
Why are causes ordered rather than listed alphabetically?
Because the order is the useful part. P0420 reads as a failed catalytic converter and is frequently a lazy downstream oxygen sensor or an exhaust leak instead. Listing all three as equals would be accurate and useless. Ordering them by how often each turns out to be the answer is what converts a definition into guidance.
How do you decide which tool tier a code needs?
By what the diagnosis physically requires. A code you can act on by reading and clearing needs a basic reader. One diagnosed by watching values change needs live data. One that needs a component commanded and watched needs bidirectional control, and there is no cheaper substitute for that. The tier is the capability, not the price.
How is the product catalog built?
Products are pulled from a live product API by category, then filtered: anything without an image, without a price or outside a sanity price band for its category is rejected rather than patched, and near-duplicate listings within a category are collapsed to the cheaper one. Capability flags are read from listing titles only where the listing states them outright.
Do you accept payment for placement?
No. No brand has paid for a tier position, a top pick or inclusion anywhere on this site. The affiliate relationship is disclosed once in the footer of every page and does not influence the ordering, which is capability first and price second within a capability tier.