PULSCAR ANALYSIS - P0404 (EGR VALVE CIRCUIT RANGE/PERFORMANCE) AND SISTER CODES 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/p0404-code ------------------------------------------------------------------------------ Prepared October 2026. Source data: NHTSA public flat files (complaints received 1 January 2015 to 4 October 2026 - the latest received date in the files; manufacturer communications; recalls since 2010) and documents downloaded one at a time from static.nhtsa.gov and nhtsa.gov. Every number in the article that is not a quotation comes from these files or from a stated computation. 1. Complaints (1,390) First search (1,100): every complaint whose narrative names P0404, P0405, P0406, P0407, P0408 or P0409 by any spelling we searched (a letter O for zero, a space, hyphen or period after the P, the suffix 00, or a bare 404 to 409 after "code", "DTC", "error", "CEL", "coded" or "fault"), or a sister code (P0400 to P0403), or a maker EGR code (P0487 to P0490, P1403, P1404, P1406, P1408, P2412 to P2415), or the words EGR or exhaust gas recirculation (the abbreviation "e.g." is not counted). Nothing was sampled: every narrative the searches returned was sorted. The text searches are written out in codebook.txt. Second search (290): an independent search of the same file for what the first one missed, run after the first batch was sorted; every complaint it proposed that meets the unchanged relevance rule was added. found_by in the complaints file says which search found each one. 238 of the 290 only cite the number of an EGR recall; 52 are owner spellings (ERG, AGR, re-circulation, DPFE). Sorting: the sorting rules (codebook.txt) were written, dated and fingerprinted before any complaint was sorted; an addendum for the second batch, which also lists the recall numbers that are EGR campaigns, was fingerprinted before that batch was sorted. A first sorting of the first half of the second batch was discarded because the sorters had not yet been given the list of EGR recall numbers (119 of 145 came back as not relevant); that half was sorted again with the addendum, and only the second sorting is used. Every complaint was sorted twice, independently, by the same written rules; each sorter saw the matching excerpt (about 300 characters either side of each matching word) or the whole narrative when nothing matched. Agreement over all 1,390: category 1,227 (88.3%); stall 1,346 (96.8%); nostart 1,380 (99.3%); recall 1,366 (98.3%); returned 1,344 (96.7%). Settling: every disagreement 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 60 complaints on which both sortings had agreed, under the same rules (mostly R1: a valve stated as replaced is category V; R11: an open recall with the part not yet available and no failure is category U; R2: EGR only in a bare list of other repairs is not relevant). The resolution column says which complaints were changed. Result: 1,296 relevant, 94 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. The NHTSA form flags (fire, crash, injury, tow) are as filed by the consumer or the agency and were not changed. 2. Documents (998 index entries mentioning EGR or an EGR code; 312 requested, 272 files with a text, 241 distinct documents) First search: NHTSA's index of manufacturer communications, entries whose summary names an EGR code (P0400 to P0409, P0487 to P0490, P1403, P1404, P1406, P2413, P2414) or the words EGR or exhaust gas recirculation: 998 entries. Heavy-truck and bus entries (344) were set aside; so were passenger and light-truck entries that mention EGR only in passing (357, mostly cooler recall notices and flash lists) and entries that name only P0401 without discussing the valve (28). The remaining 276 were requested. Second search: 36 more entries found by the independent search (sibling revisions, papers that describe the valve without the letters EGR). Of the 312 requested, 19 heavy-truck or bus papers were not downloaded, 21 entries have no file on NHTSA, and 272 files have a text (downloaded, or reused from earlier work); 3 more heavy-truck papers were set aside after download. 164 representative documents were read in full; 105 further files (revisions, copies and look-alikes of those) were compared with the representative line by line. Eight recall filings (Part 573 reports, owner and dealer letters, NHTSA acknowledgements) were read in full. Papers that were scans were read from page images, and only text that could be checked against the printed page was quoted. 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 the authors' computation from printed terms. duplicate_of marks exact copies (same text as another file): 31 of the 272 files are exact copies, leaving 241 distinct documents. 3. Owner-reported amounts (88 figures in 78 complaints) One written inclusion rule (amounts/RULE 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 the EGR valve (with its motor or position sensor), an EGR sensor, the EGR connector or wiring, cleaning the EGR valve or passages, the EGR cooler or an EGR tube or hose, or the part price of one of these, on that vehicle. Excluded: mileage written as "NNk"; vehicle prices, values, payments, trade-ins, buybacks, refund demands and settlement sums; engine, head gasket, turbo, transmission, fuel pump, computer and brake repairs; totals that mix EGR work with other major work unless the owner attributes the figure to the EGR repair; restatements; other owners' costs; rental-car costs. Status comes from the owner's own words (paid, billed, quoted, not stated); group is valve, cleaning, sensor, wiring, cooler, tube, mixed or diag. 232 candidate figures were excluded; the reason for each is in p0404-excluded-figures.csv. 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 valve 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. Motorcycles, powersports, motorhome chassis, buses and Class 7-8 trucks are outside the study and are sorted not relevant. Three groups (178 Chevrolet Volt complaints, 283 Ram, Jeep and Dodge complaints citing the EcoDiesel EGR cooler or its recalls, and 245 BMW complaints) make up more than half of the relevant complaints; shares for the whole set are dominated by them, and the article separates them where it matters.