Ford diagnostic trouble codes
Each of these is a worked diagnosis, not a code definition. What the code actually measures, the causes in the order worth testing them, the live data that separates them, and the mistakes that put the same truck back in your bay.
10 codes published so far, across 7 fault families. We are not publishing a stub for every code in the catalog — a page goes up when there is a real diagnosis to write. The next ones are chosen from what technicians actually land on here.
Misfire
Cylinder 1 Misfire Detected
What P0301 means on a Ford, how the PCM decides cylinder 1 is missing, the differential in test order, which misfire-counter and fuel-trim PIDs to pull, and the traps that cause comebacks.
Read the P0301 guideRandom / Multiple Cylinder Misfire Detected
P0300 on a Ford: why "random" changes the whole approach, how to read misfire counters and fuel trims together, what recent fuel fill and cold-start behaviour tell you, and the traps that turn a diagnosis into a parts bill.
Read the P0300 guideFuel trim
System Too Lean Bank 1
P0171 on a Ford EcoBoost or Coyote: what "too lean" actually means, why P0171 alone reads differently from P0171 with P0174, which fuel-trim PIDs to pull, and how to separate a vacuum leak from a MAF from a fuel-supply problem.
Read the P0171 guideSystem Too Lean Bank 2
P0174 on a Ford V6 or V8: why bank 2 alone means something different from both banks lean, which cylinders are on bank 2, and how the idle-versus-load fuel-trim comparison decides the repair.
Read the P0174 guideEVAP
Evaporative Emission System Leak Detected — Large Leak
P0455 on a Ford: what a "gross leak" means, why the fuel cap really is the first check, when to stop trusting the cap and start smoke-testing, and how the EVAP monitor decides whether your repair worked.
Read the P0455 guideEvaporative Emission System Leak Detected — Small Leak
P0442 on a Ford: what makes a small leak different from a gross leak, why the smoke test is not optional, how the monitor enable criteria affect confirming the repair, and what a multi-leak code cluster really means.
Read the P0442 guideOlympus resolves descriptions for the full Ford DTC catalog in-product — over 36,000 codes — and works the diagnosis live against the vehicle. These written pages are the subset we have worked through in public. Tell us which code you want next.
FutureAI is an independent software company. We are not affiliated with, endorsed by, or sponsored by Ford Motor Company. Ford, Lincoln, F-150, Ranger, Bronco, Explorer, Escape, Edge, Transit, Mustang, EcoBoost, Power Stroke, FDRS and PTS are trademarks of Ford Motor Company, used here only to identify the vehicles and tools these pages describe.