PULSCAR ANALYSIS - P0521 AND P0520 (ENGINE OIL PRESSURE SENSOR / SWITCH) AND OIL PRESSURE WARNINGS 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/p0521-code ------------------------------------------------------------------------------ Scope and dates. Prepared October 2026 from NHTSA's public flat files: owner complaints received from 1 January 2015 to 4 October 2026 (the latest received date in the files) and the index of manufacturer communications, plus the maker papers themselves from static.nhtsa.gov. The NHTSA complaint file is public: anyone can download it from NHTSA and check any number here against it. 1. Complaints counted (3,010) 715 complaints whose narrative names P0520, P0521, P0522, P0523 or P0524 (or P06DD, P06DE, P1520 to P1524) or an oil pressure part (sensor, switch, sender, gauge, module); a random sample of 1,500 of the 2,356 that matched only oil pressure warning wording; and 795 more found by a second search of the whole file. The exact search wording is in codebook.txt. found_by in the complaints file says which search found each complaint. Each complaint was sorted twice by the same written rules (codebook.txt), into one cause category and four yes/no questions (stall, damage, recall, returned); disagreements were settled by those rules (rule_applied column). The two sortings matched on the cause for 91.3% (2,747 of 3,010). Result: 2,748 relevant, 262 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. 56 complaints spell out one of P0520 to P0524 (codes_named column); the rest describe oil pressure events in the owners' words, which is why the set is built on wording as well as on codes. 2. Documents (p0521-documents.csv) 505 files of maker papers (bulletins, campaigns, special coverage, service updates), chosen from NHTSA's index by what the index summary says; one chosen entry has no file and is listed as "no file". The list shows, for each file, which of the codes P0520 to P0524, P06DD, P06DE, P06DA and P1520 to P1524 its own text names, whether it mentions an oil pressure sensor or switch, and its relevance. Recall filings and NHTSA investigation papers are not part of this set. Years, engines, build dates and coverage terms are as printed in the documents. Coverage status "as of September 2026" is our computation from printed terms. 3. Owner-reported amounts (314 figures in 251 complaints) 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 tied to the oil pressure event on that vehicle (sensor or switch, gauge, oil pump or oil-circuit part, oil leak repair, oil change, engine). Excluded: mileage written as "NNk"; vehicle price, value, payments, trade-ins, refund demands and settlement sums; repairs of other systems; totals that mix other major work; restatements; other owners' costs; rental-car and towing costs. Status comes from the owner's own words (paid, billed, quoted, not stated). 799 candidate figures were found and 485 were excluded, each with its reason in p0521-excluded-figures.csv. 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 describe the sorted complaints, not all cars and not the whole complaint file. Not every matching narrative was sorted: 856 that matched only the warning wording were left out of the sample (complaints-not-sorted.txt), and the second search stopped at a limit of 800 listed complaints, with about 1,000 more narratives of the same kind found and not sorted. The sorted set therefore understates how many complaints of this kind exist. Only 56 complaints spell out P0520 to P0524. Many complaints do not say whether the pressure itself was measured, so a warning lamp in a narrative is not proof that the oil pressure was low. The cause category is the least certain field; that is why the article reports the share of complaints where no cause was stated. The document set holds what NHTSA's index lists and what could be read; a maker paper that is not in the index is not in it.