# WhyLamp > Why the light is on. The car already stored a short check-engine code. The dashboard will not say the name. WhyLamp (whylamp.com) turns a check-engine code into a plain-English reading with sources: name, system, urgency, what a driver can check, what a shop will look at, and what is unknown. Why it exists: today’s cars store a short code and turn on the check-engine light. The name of the problem is already inside the car. A shop often charges for the first hour just to plug in a scanner and read that name. WhyLamp shows the name so the first answer is not a trip to the counter. Privacy: WhyLamp will never share or sell personal data. Policy: https://whylamp.com/privacy Terms: https://whylamp.com/terms WhyLamp is not a mechanic, not a parts store, and not legal advice. It does not invent repairs or part prices. It does not book shops or rank parts. ## Plans - Lookup (Free, live): Type the code from a scanner. Read what it means. - Garage (Membership, waitlist): Save this car’s codes in one place. - Reader kit (Membership + device, waitlist): Garage plus a small tool that reads the code from the car. Lookup is free and live. Garage and Reader kit are listed; checkout is not open; no invented monthly price. ## How codes work Many codes share a public name on most cars from 1996 on. Some codes belong to the brand and can mean different things by make. Even a shared name can need different checks by year. Make and model are requested so a note about this car is added only when we have a source. Public catalog: https://whylamp.com/codes Safety notes: https://whylamp.com/news Lookup: https://whylamp.com/#lookup Plans: https://whylamp.com/#plans Story: https://whylamp.com/#why Candela (on-site guide): ask about the check-engine light, then look up a code. Not a mechanic. ## Codes with a reading - P0420: Catalyst System Efficiency Below Threshold (Bank 1) — https://whylamp.com/code/P0420 - P0300: Random/Multiple Cylinder Misfire Detected — https://whylamp.com/code/P0300 - P0171: System Too Lean (Bank 1) — https://whylamp.com/code/P0171 - P0455: Evaporative Emission System Leak Detected (large leak) — https://whylamp.com/code/P0455 - P0442: Evaporative Emission System Leak Detected (small leak) — https://whylamp.com/code/P0442 - P0133: O2 Sensor Circuit Slow Response (Bank 1 Sensor 1) — https://whylamp.com/code/P0133 - P0401: Exhaust Gas Recirculation Flow Insufficient Detected — https://whylamp.com/code/P0401 Unknown valid codes are researched from public pages. Only text from those pages is published. If a page does not name it, we say we do not have a reading. Invalid codes 404. ## Safety notes A daily pass publishes U.S. safety recalls and industry notes. A recall is not a diagnosis. RSS: https://whylamp.com/news.xml - None stored yet. ## FAQ ### What does WhyLamp do? You type the five characters from a scanner. Later you can pull them with a WhyLamp plug-in tool. We show the name in everyday words, how soon to act, what you can check, and links to our sources. We do not invent a repair or a part price. ### Why does this exist? Doesn’t the car already know? Yes. The car stores a short code and turns on the check-engine light. The dashboard usually will not say the name of the problem. A shop often charges for the first hour just to plug in a scanner and read that name. WhyLamp shows you the name so the first answer is not a trip to the counter. ### If the check-engine light is flashing, should I keep driving? The U.S. EPA says a flashing check-engine light means the engine is skipping badly. Slow down and get help. Driving on can damage the part that cleans the exhaust. ### What can I buy? Looking up a code is free. You can do it now. Garage will save this car’s codes in one place. The Reader kit is Garage plus a small tool that plugs in under the dashboard. Garage and the kit are not for sale yet. We do not book shops or rank parts. ### What if my code is not already on the site? If the five characters are a real code, we open public pages that name it. We keep only what those pages say. If we cannot show a source, we say we do not have a reading yet. We do not invent a meaning from memory. ### Are codes the same on every car? Many codes share the same name on most cars from 1996 on. Some codes belong to the brand and can mean different things. Even a shared name can need different checks by year. That is why we ask for make and model, and why we will not guess. ### Do you track recalls? Yes. We publish U.S. safety recalls on the Recalls page, with a link to the source. A recall is not a finding that this is your car. It is not the same as looking up your code. If a scanner printed five characters, look up the code. ### Do you sell or share my data? No. We will never share or sell your personal data. Not to advertisers, brokers, shops, or parts stores. Read the privacy policy for the full list. ### Who is Candela? Candela is WhyLamp’s guide on the site. She can help you get from the check-engine light to what the code means, and tell you which plan fits. She will send you to look up a code. She is not a mechanic. ### Are you a mechanic? No. Not a mechanic, not a parts store, and not legal advice. A link sits on every definition. ## Sources - SAE J2012 Diagnostic Trouble Code Definitions: https://www.sae.org/standards/content/j2012_202509/ - U.S. EPA on-board diagnostics: https://www.epa.gov/state-and-local-transportation/vehicle-emissions-on-board-diagnostics-obd - U.S. EPA OBD FAQ (flashing MIL = severe misfire): https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1009Z15.txt ## Contact Site: https://whylamp.com