PULSCAR CODEBOOK — OXYGEN-SENSOR COMPLAINTS BEHIND THE CONVERTER (P0137 / P0136 / P0139 / P0140 STUDY; NHTSA, 2015 TO 4 OCTOBER 2026)
Published alongside https://www.pulscar.io/blog/p0137-code . License: CC BY 4.0.

The codebook below was written before any complaint was coded, dated and hashed:
2026-10-07T10:01:53Z  (UTC time of hashing)
b8c170580c6b27f1805f44898ea710fcf630a19e1c9a93cef12cb6a3f9356e21  codebook.md

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# Codebook — complaints about the oxygen sensor behind the catalytic converter (P0137 / P0136 / P0139 / P0140 study)

Written before any complaint in the set was coded.

## Pool (how the complaints were found)
NHTSA complaints received 2015-01-01 to 2026-10-04 (782,908 narratives). A complaint is in the pool if its narrative
matches any of three case-insensitive regular expressions (Python `re`):

1. A sensor-2 (behind the converter) oxygen-sensor code, bank 1 or bank 2 — the four target codes P0136, P0137, P0139,
   P0140, their bank-2 twins P0156, P0157, P0159, P0160, and the neighbours P0138, P0158 (high voltage), P0141, P0161
   (heater), P0036-P0038, P0056-P0058, P013A-P013F, P014A, P014B, P2270-P2273. Letter O for zero, a space, hyphen or
   period after the P, and an optional "00" suffix are allowed:
   `(?<![A-Z0-9])P\s?[-.]?\s?(?:[0O]136|[0O]137|[0O]138|[0O]139|[0O]14[0O]|[0O]141|[0O]156|[0O]157|[0O]158|[0O]159|[0O]16[0O]|[0O]161|[0O][0O]36|[0O][0O]37|[0O][0O]38|[0O][0O]56|[0O][0O]57|[0O][0O]58|[0O]13[A-F]|[0O]14[AB]|227[0-3])(?:\s?[-:]?\s?[0O]{2})?(?![0-9A-F])`
2. A bare number after a code word: `\b(?:code|codes|dtc|dtcs|error|cel|coded)\W{0,6}#?\s?0?(?:136|137|138|139|140|141|156|157|158|159|160|161)\b`
3. Oxygen-sensor wording: `\b(?:o2|02|o\s2|o-2|oxygen|lambda|a/f|af|air[\s/-]*fuel(?:[\s-]+ratio)?|afr)[\s-]*(?:\(\w+\)\s*)?sens[oe]r|\bH?O2S\d*\b|\b(?:o2|02|oxygen)\s*(?:cen|sen)s?[oe]rs?\b|\bHEGO\b|\bHO2\b|(?:up|down)\s?stream\s+(?:\w+\s+){0,1}sensors?|sensors?\s+(?:before|after|behind)\s+the\s+cat\w*|cat\w*\s+converter\s+sensors?`

The codes are rare in owners' words, so the study reads every complaint about an oxygen or air-fuel ratio sensor and
records, for each one, which sensor it concerns. The question for the article is the sensor behind the converter, so
the downstream flag below carries the study; complaints that place the sensor upstream or nowhere are coded too, and
the article says how many of each.

For each complaint record exactly one CATEGORY and four yes/no FLAGS.

## RELEVANCE

N — Not about an oxygen-sensor fault on this vehicle. The match is a false one ("02" that is not an oxygen sensor, a
    code that is not an oxygen-sensor code, a glow-plug or diesel NOx sensor), or the oxygen sensor is mentioned only
    in general or hypothetical terms ("it could be an O2 sensor", "unlike an O2 sensor") with no oxygen-sensor code,
    reading, diagnosis, repair or quote on THIS vehicle. If an oxygen sensor on this vehicle was diagnosed, replaced,
    quoted, named in a code, or named by a shop or scan tool as faulty, the complaint is NOT N, even if the rest of
    the complaint is about something else. A recall or coverage notice about oxygen sensors with no oxygen-sensor
    code, diagnosis or repair on the vehicle is N. An oxygen sensor named only as a location or only in another
    person's hypothesis is N.

## CATEGORY (one letter) — what the complaint states as the cause of, or the fix for, the oxygen-sensor fault or code

E — Engine mechanical cause or engine failure. The complaint states that an engine fault is behind the oxygen-sensor
    reading, code or damage (oil or coolant leaking onto or into the sensor or its wiring, oil burning, coolant in the
    cylinders, a head gasket, timing chain or cam fault, an engine that failed, seized, knocked or was replaced), OR the
    engine failed or was replaced and an oxygen-sensor code or sensor replacement appears among the other codes or
    repairs. A shop recommending, quoting or performing an engine-internal repair for the same persisting fault is E.

F — Fuel, air or ignition cause. A misfire, spark plug or ignition coil, fuel injector, fuel pump or pressure, bad fuel,
    a vacuum or intake air leak, a mass air flow or other intake sensor, a throttle body, the PCV system, the EGR or the
    evaporative system, a crankshaft or camshaft position sensor is stated as the cause of the oxygen-sensor code or
    reading, or was the repair that resolved it, without E.

C — The catalytic converter. The converter (clogged, failed, melted, inefficient, recalled, stolen, replaced, quoted or
    recommended for replacement, or a catalyst code P0420 / P0430 that the shop treats as the cause) is stated as the
    cause, or was replaced or quoted as the repair for the oxygen-sensor fault or the same check-engine light, without
    E or F. A converter replaced "because of" a sensor-2 code counts. Converters replaced for an unrelated problem do
    not.

X — Exhaust leak or exhaust part other than the converter. A leak, a cracked exhaust manifold or pipe, a manifold or
    flange gasket, a muffler, or exhaust damage is stated as the cause, or was repaired or quoted as the repair,
    without E, F or C.

W — Wiring, connector, fuse or physical damage to the circuit. A harness, connector, pin, fuse, relay, ground,
    rodent-chewed wire, melted or burned wire or connector, water in a connector, connectors swapped or misrouted,
    a TIPM or fuse/relay module, without E, F, C or X.

M — Computer or software. A reprogram, reflash, software update or calibration of the engine or powertrain computer,
    or replacement of the ECM/PCM, is the stated fix or diagnosis, without E, F, C, X or W. Includes a dealer applying
    a bulletin or campaign that consists of software.

S — The sensor itself. An oxygen or air-fuel ratio sensor was diagnosed as failed, replaced, quoted or recommended
    for replacement (once or repeatedly, whether or not it fixed the problem), and no cause in E, F, C, X, W or M is
    stated.

U — Undiagnosed or not stated. An oxygen-sensor code, warning or suspicion on this vehicle is reported, but no
    diagnosis, repair, quote or recommendation is stated (dealer found nothing, owner has not taken it in, the code is
    one of many listed with no diagnosis of it, the owner only suspects the sensor, the owner cannot say which part was
    replaced).

Precedence when more than one fits: E, then F, then C, then X, then W, then M, then S, then U. A cause counts when the
complaint (owner, shop, dealer or maker) states it as the cause of the oxygen-sensor code, reading or damage, or as the
repair done or quoted for it, or — for E only — when the engine failed or was replaced with an oxygen-sensor code or
repair among the others. A cause the owner merely guesses at, or hedges ("believed", "might", "may", "could be",
"suspected"), does not count; a cause a shop, dealer, scan tool or maker named does. A repair done for a different,
unrelated problem in the same complaint does not count (except E as defined). A bare list of parts replaced for a
general symptom (stalling, power loss, a smell, a code that is not an oxygen-sensor code) with no diagnosis stated and
nothing resolved does not set the category; if the oxygen sensor is among them, S. Parts replaced specifically for the
oxygen-sensor code, or for the same check-engine light after an oxygen-sensor repair, count as repairs done for it.
Separate diagnoses for separate codes on one scan (a misfire, an oil pressure sensor, an oxygen sensor) are separate
faults: the oxygen-sensor diagnosis stands alone. A code or scan reading that only names an oxygen-sensor code, or a
shop that only says "problem with the O2 sensor" without saying it failed or needs replacing and without a repair, is U;
a shop or parts store saying the sensor is bad, failed or needs replacing is S.

## FLAGS (yes/no)

upstream — the complaint places the oxygen sensor (or one of them) upstream: it says upstream, front, pre-catalyst,
    primary, sensor 1, bank 1 sensor 1, bank 2 sensor 1, B1S1/B2S1, "air fuel ratio" or "A/F" sensor, OR it names an
    upstream code (P0130-P0135, P0150-P0155, P0030-P0032, P0050-P0052, P014C-P014F, P015A-P015D, P2A00, P2A03,
    P2195-P2198, P1133, P1153). "Both" or "all" oxygen sensors replaced counts as yes.

downstream — the complaint places the oxygen sensor (or one of them) downstream: it says downstream, rear, post-catalyst,
    secondary, after or behind the converter, sensor 2, bank 1 sensor 2, B1S2/B2S2, OR it names a sensor-2 code
    (P0036-P0041, P0056-P0061, P0136-P0141, P0156-P0161, P013A-P013F, P014A, P014B, P2270-P2273). "Both" or "all" oxygen
    sensors replaced counts as yes. A catalyst code (P0420/P0430) alone does NOT make this yes. Plural "oxygen sensors"
    without "both", "all", "every" or a stated position sets neither flag; "bank 1" without a sensor number sets
    neither; "upper", "forward" and "up stream" count as upstream; "lower", "post" and "down stream" as downstream;
    sensors "#1 and #2" set both.

drivability — the owner describes the engine stalling or shutting off, hesitation or stumbling, surging, rough running or
    rough idle, misfiring felt by the driver, loss of power or acceleration, limp or reduced-power mode, or hard
    starting / no start (recorded for the vehicle, not tied to the sensor). A warning light, a smell, poor fuel economy,
    vibration or shaking alone, harsh shifting are not drivability.

returned_after_repair — the same oxygen-sensor code, warning light or symptom came back after a repair the complaint names
    (sensor, wiring, software, exhaust, converter, engine or any other repair done for this fault). A repair that "did
    not fix it" counts; a repair still pending does not; clearing codes does not; a different failure afterwards does
    not. Repeated replacement of the same sensor ("two or three times", "every 75k miles") counts.

## Output
One line per complaint, in the order given:
odino,category,upstream,downstream,drivability,returned_after_repair,note
category is one of N E F C X W M S U. flags are yes or no (lowercase). N complaints get all four flags = no. note = at most
12 words, no commas, no quotes, saying what drove the category.

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ADDENDUM FOR THE 98 COMPLAINTS ADDED BY THE COMPLETENESS AUDIT
Written before any added complaint was coded, dated and hashed:
2026-10-07T10:22:49Z  (UTC time of hashing)
16b48d2425ed12259c973d51903fe61cd2c5dd245dc0c1279ac6e03a5f1948a1  codebook_addendum.md

# Codebook addendum — completeness-audit additions (P0137 study)

Written before any added complaint was coded. The codebook (codebook.md, sha256 b8c170580c6b27f1805f44898ea710fcf630a19e1c9a93cef12cb6a3f9356e21, 2026-10-07T10:01:53Z) is
unchanged: same relevance rule, categories N E F C X W M S U, precedence E F C X W M S U, flags upstream, downstream,
drivability, returned_after_repair, same output format.

## What the added complaints are
An independent completeness audit searched the same narratives for what the three pool expressions missed and read every
hit. It added 98 complaints of these kinds: misspelled or split sensor wording ("O2 censor", "oxygen 2 sensor", "02
sender", "sunsor"), a bare "O2" with no sensor word, a sensor in the exhaust named without O2 wording ("exhaust sensor",
"fuel air sensors before and after the catalytic converter", "catalyst monitor sensor"), and oxygen-sensor codes outside the
first list (P0030-P0035, P0050-P0055, P0130-P0135, P0150-P0155, P2195-P2198, P2A00-P2A03: all upstream codes). Read
"oxygen sensor" in the codebook as including these spellings and descriptions. A "catalytic converter sensor" or
"upstream/downstream sensor" on a gasoline engine is an oxygen sensor; a NOx, exhaust-gas-temperature, particulate or
diesel-exhaust-fluid sensor is not. A post-catalyst fuel-trim code (P2096, P2097) or a catalyst-efficiency code (P0420,
P0430) alone is not an oxygen-sensor code: without an oxygen-sensor diagnosis, repair or quote the complaint is N.

## Rules written while the calibration set and the first 690 pool complaints were adjudicated (apply them)
R1 N rows carry all four flags = no.
R2 "All four" / "4 O2 sensors" on a V6, or "both" sensors, sets upstream and downstream = yes; "two" does not. "O2 sensor #1 ... the second O2 sensor" sets both.
R3 An owner's own inference, guess or link is not a diagnosis; the category stays S or U unless a shop, dealer, scan tool or maker states the cause.
R4 returned_after_repair = yes when a repair the complaint names (a replaced sensor, a list of replaced parts, a dealer repair) did not stop the fault or the same light or symptom; a repair still pending, ordered but not fitted, refused, or "dealer found nothing" is no; a later, different failure years afterwards is no.
R5 Throttle body, idle air control valve, purge valve, EVAP valve, fuel cap, EGR, coil, plug, injector, PCV hose and camshaft or crankshaft position sensors are F.
R6 Separate codes on one scan with separate diagnoses are separate faults: the oxygen-sensor code with no diagnosis of its own is U.
R7 Hard starting, delayed driveaway, unexpected revving or a disrupted idle counts as drivability.
R8 When a shop or dealer DIAGNOSED several parts as faulty for the same symptom or light (a list that includes the oxygen sensor and an E, F, C, X, W or M part), the diagnosis is stated and the highest-precedence part sets the category. A list of parts only REPLACED, with no diagnosis, stays S.
R9 A part a shop replaced in sequence for the same check-engine light (fuel cap, converter, PCM) counts as a repair done for the fault.
R10 A part damaged BY the failed sensor (a PCM that "burnt out because of the sensors") is a consequence, not a cause: stays S.
R11 A service-bulletin number cited alone, with no code, diagnosis or repair on this vehicle, is N. An O2 sensor named only as someone else's possible cause, or as a troubleshooting aside in an unrelated complaint (frame rust, battery acid), is N.
R12 Cleaning an oxygen sensor during an unrelated repair, with no oxygen-sensor code or diagnosis, is N.
R13 An owner's claim that sensors are bad, without a shop or tool diagnosis, is U.
R14 Rust stated as the reason oxygen sensors were bad or replaced, with no other cause in E-M, leaves S.
R15 An engine failure (failed, seized, pistons, head gasket, timing chain) with an oxygen-sensor repair or code among the others is E.

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ADJUDICATION RULES (full list, R1-R21; R1-R15 were already given to the coders in the addendum)
Written while every disagreement between the two coders was read, before the final file. R14-R21 were added as the
second batch and the consistency pass were read. Each disagreement (152 in the main pool, 14 in the audit batch, 26 in the
calibration set) was read in full and decided under these rules; the consistency pass changed 22 further codes, each with its
reason in the published CSV (column rule_applied).

# Adjudication rules (written while reading every disagreement; published in codebook.txt)
(calibration-derived, applied from the start)
R1 N rows carry all four flags = no.
R2 "all four" / "4 O2 sensors" on a V6 or "both" sensors sets upstream and downstream = yes; "two" does not (codebook).
R3 An owner's inference, guess or link ("obviously the injector failure killed the sensor") is not a diagnosis; the category stays S/U unless a shop, dealer, scan tool or maker states the cause.
R4 returned_after_repair = yes when a repair the complaint names (including a replaced sensor, a list of replaced parts or a dealer repair) did not stop the fault; a still-pending repair, a refused repair or "dealer found nothing" is no.
R5 Throttle body, idle air control valve, purge valve, EVAP valve, fuel cap, EGR, coil/plug/injector and camshaft or crankshaft position sensors are F (codebook).
R6 Separate codes on one scan with separate diagnoses are separate faults: the oxygen-sensor code with no diagnosis of its own is U.
R7 Hard starting, delayed driveaway or a disrupted idle counts as drivability.
(chunk c1 onward)
R8 When a shop or dealer DIAGNOSED several parts as faulty for the same symptom or light (a list that includes the oxygen sensor and an F, W, M or E part), the diagnosis is stated and the highest-precedence part sets the category (E, F, C, X, W, M before S). A list of parts only REPLACED with no diagnosis stays S (codebook, bare list).
R9 A shop that sequentially replaced a part for the same check-engine light (fuel cap, converter, PCM) counts as a repair done for the fault (codebook "parts replaced for the same check-engine light").
R10 A part damaged BY the failed sensor (a PCM that "burnt out because of the sensors") is a consequence, not a cause: stays S.
R11 A service-bulletin number cited alone, with no code, diagnosis or repair on this vehicle, is N.
R12 Cleaning an oxygen sensor during an unrelated repair, with no oxygen-sensor code or diagnosis, is N.
R13 Owner's claim that sensors are bad, without a shop or tool diagnosis, is U.
R14 Complaints that only echo an O2 sensor as a possible cause named by someone else, or as a troubleshooting aside in an unrelated complaint (frame rust, battery acid), are N.
R15 "O2 sensor #1 ... the second O2 sensor replaced" sets both position flags.
R16 A part that a shop replaced in an earlier visit for the same light and that did not stop it counts for returned_after_repair even if the later fix was by a different part.
R17 An owner's quoted maker-letter or campaign wording about the converter, with no shop diagnosis for this vehicle's sensor code, does not make the category C; a maker REMEDY that names the converter for the very code on the vehicle (recall remedy) does.
R18 Flex plate, pistons, head gasket, timing chain or an engine "rebuild/replace" are engine causes (E).
R19 A complaint that only quotes a recall's description or someone else's repair sequence is N.
R20 Unintended acceleration or revving without driver input counts as drivability (surging); an unwanted no-start counts too.
R21 (consistency pass) a shop or dealer saying X and the oxygen sensor 'needed to be replaced' for the same symptom is a stated diagnosis: X sets the category when X outranks S (R8). Lists the owner says were only replaced stay S.

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POOL HISTORY
First search (pool.py regular expressions above): 1,291 complaints (53 by a sensor-2 code, 4 by a bare number after a code word,
1,253 by oxygen-sensor wording; some by more than one). Completeness audit by an independent search that had not seen the first
search: the narratives returned by its wider searches read, 98 kept (misspellings,
words between O2 and sensor, bare O2, an exhaust sensor named without O2 wording, upstream codes outside the first list).
Total 1,389 complaints; 110 coded N (not about an oxygen-sensor fault on the vehicle).
Documents: 446 NHTSA manufacturer communication ids (incl. 18 added by a re-scan and a cross-check) (63 whose index summary names one of the eight target codes, 111 with oxygen and
downstream wording, 100+ with neighbouring sensor-2 codes, 148 selected from the audit's 398 candidates), 447 PDF files,
55 byte-identical, 392 distinct, 281 near-duplicate clusters.