PULSCAR ANALYSIS - P0306 AND P0305 (CYLINDER 6 AND CYLINDER 5 MISFIRE) IN NHTSA'S PUBLIC FILES PulsCar analysis of NHTSA public data, October 2026. License: CC BY 4.0 Attribution: "PulsCar analysis of NHTSA public data, October 2026." Published alongside https://www.pulscar.io/blog/p0306-code ------------------------------------------------------------------------------ Prepared October 2026. Source data: NHTSA public flat files (complaints received 1 January 2015 to 4 October 2026 were searched (4 October is the latest received date in the files; the latest matching complaint was received on 30 September 2026); manufacturer communications; recalls since 2010) and documents downloaded one at a time from static.nhtsa.gov. 1. Complaints (601) First search (426): every complaint whose narrative prints P0305 or P0306 by any spelling we searched (a letter O for zero, a space, hyphen or period after the P, the suffix 00, or a bare 305 or 306 after "code", "DTC", "error", "CEL", "coded" or "fault"), or names cylinder 5 or cylinder 6 in owners' words (cylinder 5, cyl #6, 5th cylinder, number six cylinder and similar) together with a misfire word (misfire, missing, misses, firing). Second search (175): an independent search of the same file for what the first one missed (other spellings, typed cylinder words, cylinder wording without the word misfire, part faults on cylinder 5 or 6 with a running symptom); every complaint it proposed was added to the set and sorted by the same unchanged rules, and the sorting decided whether it was relevant (170 were). found_by in the complaints file says which search found each complaint. Sorting: the sorting rules (codebook.txt) were written, dated and fingerprinted before any complaint was sorted. Every complaint was sorted twice, independently, by the same written rules, each time from the rules alone, without sight of the other sorting. One category (N not a misfire on cylinder 5 or 6 on this vehicle; C ignition coil; P spark plug; I fuel injector; V valvetrain, meaning lifter, rocker arm, camshaft or valve; H head gasket, coolant in the cylinder or a cracked head; E engine failure or replacement with no more specific part named; F software or a program only; O another cause; K checked and cleared; U nothing found or done yet, or parts that did not help), the cylinder named (5, 6, B for both or with other cylinders, X none) and five flags (stall or loss of power, flashing check engine light, engine replacement or major internal repair, recall or program mentioned, returned). Where the complaint gave the sorter only an excerpt around the matching words, the complete text was used when the excerpt did not decide the question. Agreement over all 601: category 573 (95.3%); cylinder 587 (97.7%); stall 561 (93.3%); flashing light 600 (99.8%); engine work 575 (95.7%); recall or program 585 (97.3%); returned 572 (95.2%). Settling: every disagreement (125 rows) was read and settled by one of the written rules R1 to R12 (listed in codebook.txt); the rule applied is in the rule_applied column. A consistency check then changed 55 agreed rows under the same rules (resolution says "changed in consistency pass"). Result: 559 relevant, 42 not relevant. Counts are counts of complaints, not cars. A complaint is evidence that an owner wrote to NHTSA; nothing here is a failure rate. 2. Documents (326 files, 280 distinct documents) First search: NHTSA's index of manufacturer communications, entries whose summary names P0305 or P0306 (246), or describes a misfire on cylinder 5 or 6 (23 more), and an independent second search (62 more files proposed, 58 with a readable PDF). Broader misfire papers that list only P0300 or a range and name no cylinder in their index summary were not downloaded unless the second search proposed them. Reading: 190 representative documents were read in full; the other files (revisions, copies and look-alikes of those) were compared with their representative line by line, and what differed is recorded. Some papers whose text did not read cleanly (7 files with no readable text, some with scrambled tables) were read from images of their pages. Every verbatim quotation in the article was checked against the text of the named document. The document list says, for each file, what was done (column read), whether its own text names P0305 or P0306, and its relevance (DIRECT: about the target fault; LISTED: a target code is one of many in a list; RELATED: a companion code or the same fault family). Model years, engines, build dates and coverage terms are as printed in the documents, never taken from NHTSA's index, which expands years. Coverage status "as of September 2026" is our computation from printed terms. exact_copy_of marks files with the same text as another file; 46 of the 326 files are exact copies, leaving 280 distinct documents. 3. Owner-reported amounts (106 figures in 86 complaints) One written inclusion rule (amounts below, fixed before the figures were decided): a dollar figure is included when the owner states it as a price, charge, bill, quote or estimate for diagnosing, repairing or replacing a part or system named in connection with the misfire on cylinder 5 or 6 on that vehicle (coil, spark plug, injector, camshaft, lifters or valves, head gasket or cylinder head, engine replacement or rebuild, diagnostic fee), or an extended-warranty or goodwill sum offered for that event. Excluded: mileage written as "NNk"; vehicle price, payments, insurance; other systems; towing alone; general figures about other owners; restatements; sums received from a maker or warranty company. Status comes from the owner's own words (paid, billed, quoted, offered, not stated): 62 quotes, 31 bills, 10 amounts paid, 2 offered, 1 not stated. Figures are what owners wrote, not audited invoices. 4. Limits The complaint file holds the cases where an owner wrote to NHTSA, in the owner's words, with no verification; owners whose trouble ended are mostly not in it. The shares reported (for example how many coil replacements were followed by a return of the problem) describe the complaints, not all cars. The document set holds what NHTSA's index lists; a maker paper that is not in the index is not in it. Amounts rule: INCLUDE a dollar figure when the owner states it as a price, charge, bill, quote or estimate for diagnosing, repairing or replacing a part or system named in connection with the cylinder-5 or cylinder-6 misfire event on THIS vehicle, or an extended-warranty/goodwill sum offered for that same event. EXCLUDE: mileage written as 'NNk'; vehicle price, payments, insurance; repairs of other systems; towing alone; figures about other owners or general averages found online; restatements of a figure already counted in the same narrative; reimbursements received from a maker or warranty company.