How codes, severities and labor estimates are built

Every tool and page reads four data files: the 164 generic codes and their causes, the dashboard lights and their rules, the technician wages by state, and the list of official sources. Nothing is typed into a page by hand: a corrected cause or a new wage table changes every page that shows it. Automated tests check the code decoder, the labor arithmetic and the warranty and clearing rules on cases worked out by hand.

1. Code meanings

OBD-II codes follow the structure of SAE J2012, which federal rules require for emission-related faults (40 CFR 86.1806-17 names it). The first character is the system, the second says whether the code is generic or defined by the maker, the third narrows the subsystem. We give each generic code its standard description and a plain-English sentence in our own words; we do not reproduce the SAE document. Codes whose second character marks them as manufacturer-specific are decoded for their structure only: their meaning is the maker's, and guessing it would mislead.

2. Causes and their order

Causes are listed from the most frequent fix to the least, as "most frequent", "frequent" or "less frequent". The order reflects how these codes are usually resolved in diagnosis guides and repair practice, not a statistic we measured: no public data set records which repair cleared which code. Two codes set together change the order, and the pages say so where it matters (P0171 with P0174, a misfire with a lean code).

3. Severity

Each code and each light state gets one of five levels. A flashing check engine light is always the top level, because the federal rule makes the light blink only when misfire is damaging the catalytic converter. Lights whose federal color is red, a loss of oil pressure, overheating and brake symptoms are also at the top. Emission-only faults with no effect on how the car drives are at the bottom.

4. Labor hours

For the 27 codes with a page, each common repair carries a range of labor hours, written by us for a typical front-engine car or light truck from the steps the job involves: access, removal, replacement, relearn and test. They are not the flat-rate book times that shops license from maker data, which vary by model and which we cannot republish. Engines where the part sits under the intake manifold or at the back of a transverse V6 take longer, and the ranges say so when it is common.

5. Starting shop rate by state

Shops set and post their own labor rates and no public agency publishes them. To give a starting figure, the tools take the mean hourly wage of automotive service technicians and mechanics in the state (BLS Occupational Employment and Wage Statistics, occupation 49-3023, May 2025) and multiply it by 4, rounded to $5, to cover the shop's overhead and margin. That multiplier is our assumption, not a measurement, which is why every result shows the rate it used and lets you type your shop's own. National mean wage: $27.13.

6. Parts

Parts are not priced. Prices vary by brand, model, region and week, and no public, dated source covers them; a figure we could not source would only look precise. The estimates are labor only and say so.

7. Rules used by the tools

The clearing tool counts 3 fault-free trips before the check engine light may go off and 40 engine warm-up cycles before a code may be erased, as written in 40 CFR 86.1806-05 for model years up to 2016 (the later rules carry the same logic through California's regulation). A warm-up cycle is a drive in which coolant rises by at least 40 °F and reaches at least 160 °F (40 CFR 86.1803-01). The warranty check uses 40 CFR 85.2103 and the California Air Resources Board's fact sheet. The tire pressure tool uses FMVSS 138 and its table of minimum activation pressures.

8. Sources read

9. What the site does not do

• It does not diagnose a car: it tells you where a diagnosis usually starts.
• It does not interpret manufacturer codes or reproduce service information.
• It keeps nothing you type: the tools run in your browser.

Method version of November 1, 2026. A figure that looks wrong: contact.