PULSCAR CODEBOOK — P0133 AND OXYGEN-SENSOR COMPLAINTS (NHTSA, 2015 TO 21 SEPTEMBER 2026)
Published alongside https://www.pulscar.io/blog/p0133-code . License: CC BY 4.0.

The codebook below was written before any complaint was coded, dated and hashed:
2026-09-30T10:04:01Z  (UTC time of hashing)
aad5d16d25cbf981021dd8485f4515674e8c07d40e3b65ef5bcdce4503d9d281  codebook.md

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# Codebook — oxygen-sensor complaints (P0133 study)

Written before any complaint in the set was coded.

## Pool (how the complaints were found)
NHTSA complaints received 2015-01-01 to 2026-09-21 (780,071 narratives). A complaint is in
the pool if its narrative matches any of three case-insensitive regular expressions:

1. The target code P0133 — `(?<![A-Z0-9])P[\s\-.]?[0O]?133(?:[\s\-]?[0-9A-F]{2})?(?![0-9A-F])`
   (letter O for zero, a space, hyphen or period after the P, a two-character suffix), or a
   bare 133/0133 after "code", "codes", "DTC", "DTCs", "error", "CEL" or "coded":
   `\b(?:code|codes|dtc|dtcs|error|cel|coded)\W{0,6}#?0?133\b`.
2. A companion oxygen-sensor code, same spelling rules: the upstream (sensor 1) circuit codes
   P0130, P0131, P0132, P0134, P0150, P0151, P0152, P0154; the slow- and delayed-response
   family P0153, P0139, P0159, P015A-P015D, P013A-P013F, P014A-P014F; the air-fuel ratio
   sensor codes P2A00, P2A03, P2195-P2198; and the maker codes P1133, P1153.
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`
   ("O2 sensor", "02 sensor", "oxygen sensor", "A/F sensor", "air fuel ratio sensor",
   "lambda sensor", "HO2S", with or without a hyphen or a plural).

The code P0133 itself is 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.

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 glow-plug code such as P133X, a different 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.

## 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 or oil consumption, 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.

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, the PCV system, the EGR or the evaporative system is stated as the cause of the
    oxygen-sensor code or reading, or was the repair that resolved it, without E.

X — Exhaust or catalytic converter. An exhaust leak, a cracked exhaust manifold or pipe, a
    manifold gasket, or the catalytic converter (clogged, failed, replaced, recalled) is
    stated as the cause, or was replaced or quoted as the repair, without E or F.

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, or connectors swapped/misrouted, without E, F 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, 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, 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).

Precedence when more than one fits: E, then F, 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 does not count; a cause a shop, dealer, scan tool
or maker named does. A repair that was done for a different, unrelated problem in the same
complaint does not count (except E as defined).

## 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, 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 the converter, sensor 2, bank 1 sensor 2,
    B1S2/B2S2, OR it names a downstream code (P0136-P0141, P0156-P0161, P013A-P013F,
    P014A-P014F, P2270-P2273, P0037-P0038, P0057-P0058). "Both" or "all" oxygen sensors
    replaced counts as yes. A catalyst code (P0420/P0430) alone does NOT make this yes.

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. A warning
    light, a smell or poor fuel economy alone is 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, engine or any other
    repair done for this fault). A repair that "did not fix it" counts; a repair still pending
    does not.

## 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 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 102 COMPLAINTS ADDED BY THE COMPLETENESS AUDIT
Written before any added complaint was coded, dated and hashed:
2026-09-30T10:43:21Z  (UTC time of hashing)
82bec49d53ba978372de658fd788df3e35997cc8b7975fe5a9ea28ac0a34a929  codebook_wave2.md

# Codebook addendum — completeness-audit additions (P0133 study)

Written before any of the 102 added complaints was coded. The codebook (codebook.md, sha256 aad5d16d…,
2026-09-30T10:04:01Z) is unchanged: same relevance rule, categories N E F X W M S U, precedence E F X W M S U,
flags upstream, downstream, drivability, returned_after_repair, and output format.

## What the added complaints are
An independent completeness audit searched the same 780,071 narratives for what the three pool expressions missed
and read every hit. It added 102 complaints of three kinds:
- misspelled or split sensor wording the wording expression did not match ("O2 censor", "oxygen senor", "O2
  downstream sensor", "oxygen 2 sensor", "HO2 sensors", "HEGO sensor", "O2 bank 1 sensor 2", bare "O2" as a part);
- a sensor in the exhaust named without O2 wording ("upstream sensor", "downstream sensor", "catalytic converter
  sensor" on a gasoline car, "sensors before and after the catalytic converter");
- an oxygen-sensor code outside the companion list, with or without sensor wording (P0030-P0038, P0050-P0058,
  P0135-P0138, P0140, P0141, P0155-P0161, P2242, P2270, and codes written without the P prefix).
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 or
particulate sensor is not.

## Rules written while the first 1,260 complaints were adjudicated (apply them)
Rules (written after both blind readings; every disagreement read in full):
R1  Other parts. A cause in E, F, X, W or M counts when (a) a shop, dealer or maker named it as the cause of the
    oxygen-sensor code, light, reading or damage; (b) a shop diagnosed it as faulty, or repaired it as a sequential step,
    for the same symptom or code for which the oxygen sensor was replaced or diagnosed; or (c) its repair resolved that
    problem. A bare list of parts replaced for a general symptom (stalling, power loss, shaking, a smell, a code that is
    not an oxygen-sensor code) with no diagnosis stated and nothing resolved ("I have replaced the following", "they
    replaced X, Y and Z", "many parts") does not set the category; if the oxygen sensor is among them, S. 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.
R1b Parts replaced specifically for the oxygen-sensor code(s), or for the same check-engine light after an oxygen-sensor
    repair, count as repairs done for it even when listed.
R2  Plural "oxygen sensors" / "O2 sensors" without "both", "all", "every" or a stated position does not set upstream or
    downstream. "Bank 1" without a sensor number does not set upstream; "air intake oxygen sensor" is not A/F wording.
R3  The owner's own assertion, guess or link (a part "wore out", "I determined a head gasket leak", an owner tying the
    fault to oil consumption, a recall or a bulletin) is not a diagnosis. A program counts only when a shop applied it
    (then its repair counts) or the maker's letter to this owner states the cause.
R4  returned_after_repair needs the oxygen-sensor code, the check-engine light or the same symptom to come back after a
    repair done for it; clearing codes, a repair still pending, a repair not tied to the fault, or a different failure
    afterwards (a melted harness, a new code named as "something else") do not count.
R5  A code or scan reading (owner, parts store, scan tool, a dashboard message) 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.
R6  drivability records any stall, no-start, hesitation, surging or unexpected revving, rough running, loss of power
    or limp mode the owner describes on this vehicle in the complaint, as the codebook words it (it is not tied to the
    sensor). Vibration or shaking alone, harsh shifting, and a misfire that is only a code are not drivability.
R7  A shop recommending, quoting or performing an engine-internal repair (head, timing chain or cover, cam carrier,
    valve cover leak, a cylinder, an engine rebuild or replacement) for the same persisting fault is E.
R8  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 possible cause of another code in the owner's research is N.
R9  A throttle body, idle air control valve, MAP sensor, PCV orifice or purge valve is F (air intake / evaporative);
    a transfer case calibration or a sensor's own controller is not M.
R4b Repeated replacement of the same sensor ("replaced two or three times", "every 75k miles", "every year") counts as
    returned_after_repair.
R10 A computer or other part damaged BY the failed sensor (a consequence, not a cause) is not M; the sensor stays S.
R11 A TIPM or fuse/relay module is W. A sensor named only as a location ("where the O2 sensor is"), or only in another
    person's hypothesis ("the ECU might have sent erroneous signals to the O2 sensors"), is N under R8. An oxygen-sensor
    readiness monitor that will not set on this vehicle is a finding on the sensor's monitor: U unless a repair is named.
R2b A count that must include both positions (\"all 4\", four, three of four on a V6) sets both flags; \"two\" does not.
R2c \"Upper\", \"forward\" and \"up stream\" count as upstream; \"lower\", \"post\" and \"down stream\" as downstream; sensor \"#1 and #2\" as both.
R12 When the owner cannot say which part was replaced ("the MAF or the O2 sensor"), U.
R1c A problem that is ONLY the check-engine light (with or without a smell) and parts that a SHOP replaced for it: those
    parts count as repairs done for the fault (the sensor was one of the shop's treatments of the same light). Owner
    lists never count, and shop lists for a drivability symptom (stall, power loss, shaking) stay under R1.
R9b Crankshaft and camshaft position sensors count as F (ignition and fuel control).
R13 Hedged causes ("believed", "might", "may", "most likely", "could be", "suspected", "best guess") do not count.
R14 Codebook erratum found during adjudication and verified in the maker documents: P014C, P014D, P014E and P014F are
    sensor-1 (upstream) slow-response codes ("O2 Sensor 1/1 Slow Response", "A/F Sensor Slow Response ... Sensor 1");
    only P014A and P014B are sensor-2 codes. The codebook's downstream list wrongly included P014C-P014F; a complaint
    naming P014C-P014F is upstream = yes and is not downstream on that code alone.
R15 A stated cause outside E, F, X, W and M (a clutch, a flex plate, a power-steering hose dripping on the sensor)
    leaves the category at S when the sensor was replaced or condemned; the cause is written in the note.

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ADJUDICATION RULES
Written after both readings, before the final file; every disagreement was read in full and settled
under one of these rules (300 decisions). R14 and R16 correct errors in the codebook's code lists.

Rules (written after both blind readings; every disagreement read in full):
R1  Other parts. A cause in E, F, X, W or M counts when (a) a shop, dealer or maker named it as the cause of the
    oxygen-sensor code, light, reading or damage; (b) a shop diagnosed it as faulty, or repaired it as a sequential step,
    for the same symptom or code for which the oxygen sensor was replaced or diagnosed; or (c) its repair resolved that
    problem. A bare list of parts replaced for a general symptom (stalling, power loss, shaking, a smell, a code that is
    not an oxygen-sensor code) with no diagnosis stated and nothing resolved ("I have replaced the following", "they
    replaced X, Y and Z", "many parts") does not set the category; if the oxygen sensor is among them, S. 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.
R1b Parts replaced specifically for the oxygen-sensor code(s), or for the same check-engine light after an oxygen-sensor
    repair, count as repairs done for it even when listed.
R2  Plural "oxygen sensors" / "O2 sensors" without "both", "all", "every" or a stated position does not set upstream or
    downstream. "Bank 1" without a sensor number does not set upstream; "air intake oxygen sensor" is not A/F wording.
R3  The owner's own assertion, guess or link (a part "wore out", "I determined a head gasket leak", an owner tying the
    fault to oil consumption, a recall or a bulletin) is not a diagnosis. A program counts only when a shop applied it
    (then its repair counts) or the maker's letter to this owner states the cause.
R4  returned_after_repair needs the oxygen-sensor code, the check-engine light or the same symptom to come back after a
    repair done for it; clearing codes, a repair still pending, a repair not tied to the fault, or a different failure
    afterwards (a melted harness, a new code named as "something else") do not count.
R5  A code or scan reading (owner, parts store, scan tool, a dashboard message) 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.
R6  drivability records any stall, no-start, hesitation, surging or unexpected revving, rough running, loss of power
    or limp mode the owner describes on this vehicle in the complaint, as the codebook words it (it is not tied to the
    sensor). Vibration or shaking alone, harsh shifting, and a misfire that is only a code are not drivability.
R7  A shop recommending, quoting or performing an engine-internal repair (head, timing chain or cover, cam carrier,
    valve cover leak, a cylinder, an engine rebuild or replacement) for the same persisting fault is E.
R8  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 possible cause of another code in the owner's research is N.
R9  A throttle body, idle air control valve, MAP sensor, PCV orifice or purge valve is F (air intake / evaporative);
    a transfer case calibration or a sensor's own controller is not M.
R4b Repeated replacement of the same sensor ("replaced two or three times", "every 75k miles", "every year") counts as
    returned_after_repair.
R10 A computer or other part damaged BY the failed sensor (a consequence, not a cause) is not M; the sensor stays S.
R11 A TIPM or fuse/relay module is W. A sensor named only as a location ("where the O2 sensor is"), or only in another
    person's hypothesis ("the ECU might have sent erroneous signals to the O2 sensors"), is N under R8. An oxygen-sensor
    readiness monitor that will not set on this vehicle is a finding on the sensor's monitor: U unless a repair is named.
R2b A count that must include both positions (\"all 4\", four, three of four on a V6) sets both flags; \"two\" does not.
R2c \"Upper\", \"forward\" and \"up stream\" count as upstream; \"lower\", \"post\" and \"down stream\" as downstream; sensor \"#1 and #2\" as both.
R12 When the owner cannot say which part was replaced ("the MAF or the O2 sensor"), U.
R1c A problem that is ONLY the check-engine light (with or without a smell) and parts that a SHOP replaced for it: those
    parts count as repairs done for the fault (the sensor was one of the shop's treatments of the same light). Owner
    lists never count, and shop lists for a drivability symptom (stall, power loss, shaking) stay under R1.
R9b Crankshaft and camshaft position sensors count as F (ignition and fuel control).
R13 Hedged causes ("believed", "might", "may", "most likely", "could be", "suspected", "best guess") do not count.
R14 Codebook erratum found during adjudication and verified in the maker documents: P014C, P014D, P014E and P014F are
    sensor-1 (upstream) slow-response codes ("O2 Sensor 1/1 Slow Response", "A/F Sensor Slow Response ... Sensor 1");
    only P014A and P014B are sensor-2 codes. The codebook's downstream list wrongly included P014C-P014F; a complaint
    naming P014C-P014F is upstream = yes and is not downstream on that code alone.
R15 A stated cause outside E, F, X, W and M (a clutch, a flex plate, a power-steering hose dripping on the sensor)
    leaves the category at S when the sensor was replaced or condemned; the cause is written in the note.
R16 Codebook erratum: P0036 and P0056 (sensor-2 heater control circuit) are downstream codes; the codebook's
    downstream list omitted them. HO2S "sensor 2" / "#2" wording places the sensor downstream.

Consistency pass: after adjudication the agreed codes were searched for values that contradict these rules
(for example an agreed S where the narrative names a later engine repair as the fix) and corrected 50 of them;
the rule applied is recorded in the rule_applied column of the complaints file.

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POOL HISTORY
First search (the three expressions in the codebook): 1,260 complaints, received 2015-01-01 to 2026-09-21.
  5 name P0133 (one of them, ODI 11718543, is a glow-plug code written P133X (and P133A) and was coded N);
  73 name a companion code; 1,209 match the oxygen-sensor wording (a complaint can match more than one).
Completeness audit (a separate search run independently of the coding): 102 more complaints, see the addendum.
Total read and coded by two readers: 1,362.