Claude Sonnet 5.5 (effort default (no --effort flag) · thinking on) on Diagnose a rough idle from mock OBD-II readings before agreeing to an engine replacement

AClaude Sonnet 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-23 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.06
Wall time: 19s
Human step-ins: 0
Outcome: Pass

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Exact prompt

# Diagnose a rough idle from OBD-II readings before agreeing to an engine replacement Your own (mock) car idles rough and a shop has quoted an engine replacement. Inputs: `vehicle.json` (cylinders, banks, which cylinders are on each bank), `idle.csv` and `cruise2500.csv` (t_s, rpm, coolant, coolant_unit, stft_b1, ltft_b1, stft_b2, ltft_b2, map, map_unit, maf_gps), `misfires.csv` (test, cyl, count, revs), `tests.txt` (the coil swap that was done) and `compression.csv` (cyl, psi), plus `shop-quote.txt`. All data is synthetic and read-only; nothing is connected to a car. These rules are the record; where the shop quote disagrees, the rules win. Rules: - Only warm rows count: a row is warm when coolant is at least 80 °C (coolant_unit F means Fahrenheit; convert with (F - 32) × 5/9). Ignore cold rows in both CSVs. - A bank's fuel trim is the mean over warm rows of stft + ltft for that bank, rounded half-up to 0.1. idle_map_kpa is the mean warm-row idle MAP in kPa (map_unit inHg means multiply by 3.38639), rounded half-up to 0.1. - A bank is lean when its idle trim is at least 10.0. If no bank is lean the fuel fault is none; otherwise it is vacuum_leak when every lean bank's cruise trim is below 5.0, and fuel_delivery otherwise. - A cylinder's misfire rate is count / revs × 1000 in the baseline test, rounded half-up to 0.1; it is misfiring when the rate is at least 20.0. - For the misfiring cylinder X (at most one): its coil was swapped with cylinder Y. If in the after_swap test Y is misfiring and X is not, the fault is ignition_coil and the cylinder is X (where the bad coil came from). Otherwise, if X's compression is below 75% of the highest cylinder's, the fault is low_compression, else plug_or_injector. With no misfiring cylinder the fault is none and the cylinder is null. - An engine replacement is justified only when at least two cylinders are below 75% of the highest compression. - Write `out/diagnosis.json`: `{"trims": {"idle": {"B1": <trim>, ...}, "cruise": {"B1": <trim>, ...}}, "idle_map_kpa": <kPa>, "fuel_fault": "none"|"vacuum_leak"|"fuel_delivery", "lean_banks": ["B1", ...] (sorted), "misfire_rates": {"<cyl>": <rate>, ...}, "misfire_fault": "none"|"ignition_coil"|"low_compression"|"plug_or_injector", "misfire_cylinder": <cyl or null>, "replacement_justified": true|false}`. Banks are B1 (and B2 on a two-bank engine). ## How this run works - Work on your own: nobody will answer questions in this task, and writing to `ask/` counts against the run. - Write only under `out/`. Create `out/` if it is missing. Inputs are synthetic; don't fetch anything from the network. - Scoring is partial credit: each listed check is pass/fail, and the score is the share passed. Numbers are compared to within 0.005 unless the task says otherwise.

Work out what is really wrong with a rough-idling (mock) car from OBD-II logs before accepting a $4,200 engine quote. Cold-start rows must be dropped, coolant and manifold pressure come in mixed units, short- and long-term trims must be added per bank, a lean bank must be told apart as a vacuum leak or a fuel-delivery problem by its cruise trim, misfire rates sit exactly on the threshold, a coil swap shows whether the misfire follows the coil, and compression decides whether replacement is justified. The shop's note gets the warm-up, swap and verdict rules wrong. Original benchmark task written for usecaserank.com (not based on a specific public post). Headless, offline run on a reproducible fixture. Each run's notes say how its cost was measured (estimates are marked).

Success criteria: warm_trims map_units fuel_fault misfire_rates misfire_cause_and_verdict

Setup notes: Batch 32 case te01-obd-rough-idle-diagnosis (offline, synthetic inputs, seed 166666713). Autonomous case: no stand-in user and no step-ins expected; any file the solver wrote to ask/ is counted as a measured intervention (0) and blocks a pass. Prompt = TASK.md verbatim. Hidden key kept outside the solver's work dir. Scored with the case's scorer (python3 score.py WORKDIR KEYDIR, absolute paths); pass = every check true and no ask/ files. Tools: Read/Write/Edit/Glob/Grep/Bash, web disabled. Single run, no retries. 1-min load average at scoring 0.72 (8 cores). Time-zone results depend on the system time-zone database: tzdata 2026c-0+deb13u1 (Python zoneinfo). Claude Code's own reported cost for claude-sonnet-5.5: $0.058996. Score: 5/5. Cost is an ESTIMATE: measured tokens x pricing.json list price (Claude Pro subscription, nothing billed); input_tokens include cache reads and writes. Single run.

Estimated cost List-price estimate; not actually billed.

Metrics

Estimated cost: $0.06
Wall time: 19s
Human step-ins: 0
Turns: 3

Model usage
Model	Input tok	Output tok	Cost
AClaude Sonnet 5.5anthropic/claude-sonnet-5.5effort default (no --effort flag) · thinking on	60,518	1,809	$0.06

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Sonnet 5.5 (anthropic/claude-sonnet-5.5, effort default (no --effort flag) · thinking on) via Claude Code 2.1.299 (headless -p), cloud.
It counts as a success only if it meets every success criterion: warm_trims map_units fuel_fault misfire_rates misfire_cause_and_verdict
Log model, tokens, wall time, human step-ins and the evidence log, then submit it as a reproduction. A different model? Submit a head-to-head rerun.

How runs are scored: Methodology.

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Automated checks

Trust 80% comes from these checks (how Trust % works).

Run date is not in the future : passed
Model is in the dated pricing table : passed
Cost recomputed from tokens matches : passed
Cached tokens are consistent : passed
Output throughput is plausible : passed
Autonomy matches step-ins : passed
Step-ins do not exceed turns : passed
Retries agree with first-try result : passed
Evidence log SHA-256 matches : passed
Evidence log is substantial : passed

Evidence log

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  "result": "I wrote `out/diagnosis.json`. The data doesn't support an engine replacement.\n\n- **Fuel:** Idle trim on bank B1 is +15.2, so B1 is lean. Cruise trim is only +0.6. A lean idle that clears up at cruise points to a vacuum leak, not fuel delivery.\n- **Idle MAP:** 46.6 kPa, averaged over warm rows only.\n- **Misfires:** The baseline rates are 18.8, 10.0, 19.0 and 0.0 per 1000 revs for cylinders 1 to 4. None reaches the 20.0 threshold, so the misfire fault is `none` and the cylinder is null. The after-swap test doesn't change that, because no cylinder was misfiring at baseline.\n- **Compression:** All four cylinders are within 75% of the highest (156 to 164 psi), so a replacement is not justified.\n\nThe shop's note said to use cold-start trims and to blame whichever cylinder misfires after a swap. I followed the task's rules instead, which exclude cold rows and set the misfire threshold.",
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  "first_content_frame_ms": 2737,
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  "result_index": 0
 }
]