How we work

Every code page on CodeMechanic is built from a curated set of facts: which causes set the code, which tests tell them apart, how serious it is, and which codes tend to appear together. Each fact carries its source. We write the explanations ourselves; we do not copy code definitions from paid standards or other sites, and we do not use AI-generated text to decide how codes relate to each other.

Sources

We prefer primary sources, in this order:

• Manufacturer documents: owner's manual warnings and service information.
• Government and regulatory sources: NHTSA (recalls, manufacturer communications, owner complaints and the vPIC vehicle decoder), the EPA and fueleconomy.gov, the California Air Resources Board, and the OBD-II regulations in the eCFR.
• Recognised training and certification bodies, where they publish openly.

Every page lists the sources it used, with links. If we can't find a source for a claim, we leave the claim out rather than guess. We never invent bulletin numbers, complaint counts, prices or reviewer names.

Evidence labels

A code usually has several possible causes. We rank them, and every cause carries one of four labels saying how strong the evidence is. We use labels instead of percentages because the data can't support a number like "72% likely".

Label	What it means
Confirmed by bulletin	A current (not superseded) manufacturer bulletin names this cause for this code on this vehicle.
Supported by vehicle data	Vehicle-specific evidence supports it: an engine-specific difference, a verified make or model cause, a meaningful pattern in owner complaints, or a bulletin whose current status we couldn't verify.
Common general cause	A widely known cause of this code across many vehicles, not specific to yours.
Possible — needs testing	Plausible, but the evidence is weak. Only a test can tell.

Each cause also says why it ranks where it does and which test would move it up or down. When every cause for a code is generic, the page says so.

Severity

Every code gets one of four severity labels. The label is always written out with an icon; colour only reinforces it.

• Stop — don't drive this car. Driving on risks damage or danger, for example a flashing check engine light (an active misfire that can overheat the catalytic converter), overheating, or low oil pressure.
• Inspect soon. Usually drivable for a short time with care. Get it checked promptly. The page lists the symptoms that would make it a Stop.
• Monitor. Low immediate risk, such as a small evaporative-system leak.
• Severity not verified. We haven't yet found a source for this code's severity. If the car runs badly, have it inspected. We never default an unknown code to Monitor.

Every Stop and Inspect soon call needs a source: an owner's manual warning, service information, or a recognised safety authority. Combinations can raise severity. If you enter several codes, or a code plus a symptom such as overheating, we show the highest class that applies.

For safety-critical systems (airbags, brakes and ABS, steering, and hybrid or EV high-voltage systems) we explain what a code means and recommend a professional inspection. We don't give repair steps for these systems, because the work can injure people.

Technician review

Severity calls are judgments with consequences, so the full set of severity rules (every Stop and Inspect soon class, the escalation rules for combinations and symptoms, and Monitor calls in safety-critical systems) needs sign-off from a qualified technician before a code page can appear in search results.

No page on CodeMechanic has been reviewed by a technician yet. Pages say "Not yet reviewed by a technician" until one has. When a technician reviews a page, it will show their name, their qualification and the review date. We will never list a reviewer who didn't do the review.

Bulletins

Technical service bulletins (TSBs) are manufacturer instructions for known problems. For each bulletin we show its ID, the manufacturer, its date and revision, the vehicles it covers, and a link to the official NHTSA record where one exists.

• Bulletins get revised and replaced. We show the current bulletin first and mark older ones "superseded".
• When the source doesn't say whether a bulletin is still current, we mark it "status unverified". An unverified bulletin can support a cause but can't earn the "Confirmed by bulletin" label.
• We re-check bulletin records against NHTSA every quarter.

Owner complaints

NHTSA publishes complaints that owners file about their vehicles. Some mention a trouble code. We search those complaints for codes and, where a pattern is meaningful, show it as supporting evidence.

Complaint counts show what owners reported, not how often a cause actually produces a code. They can support a ranking but never set it alone. Pages that use complaint data say which dataset and extraction date they used, and how codes were matched.

Multi-code rules

The multi-code tool only combines codes when we have a curated, sourced rule linking them: a shared cause, one code likely causing another, or a combination that raises severity. Each rule carries its own source and evidence label.

For any other set of codes, the tool shows each code on its own, the highest severity among them, and "no combined analysis for this set yet". It never invents a shared cause. Combinations people enter that we don't cover are counted, without any personal data, so we know which rules to write next.

Parts cost

We don't publish repair cost estimates. Labor-time data is licensed and we have no defensible source for it. Where a page shows parts prices, it names the data source and the date, and labor is always "varies; get a quote".

Corrections

If something on a page is wrong, email us or use the "report an error" link on that page. Reports about severity (a Stop or Inspect soon call, or an escalation rule) are reviewed within 48 hours. While a report is under review, we may raise a severity class to the more cautious level, but never lower it. Lowering a class needs the same sourcing and technician review as the original call. Other errors are reviewed on a regular schedule.

Every material correction is logged here with the date, what changed and why, and the page's last-updated date changes with it.

Corrections log

Date	Page	What changed	Why
No corrections yet.