Car Maintenance Timeline 🔧

"What's actually due on my car at 84,500 km?" Most owners answer this by guessing, ignoring it, or trusting a service advisor whose incentives are not aligned with their wallet. Result: missed safety services on one end, and $600 "premium packages" full of items that aren't due yet on the other.

This skill treats the manufacturer maintenance schedule as what it is — a table of dual intervals (every N km OR M months, whichever comes first) — and computes, from your odometer, in-service date, and service history, what is genuinely OVERDUE, DUE SOON, or OK, what it typically costs, and how hard it is to do yourself.

Overview

One tool, three commands (scripts/car_maintenance.py):

1. tasks — the built-in task library: 13 generic services with km/month intervals, severe-service intervals, priority class (safety-critical / wear-item / standard), typical cost range, and DIY difficulty.
2. status — per-task evaluation: last done (from --history or in-service by default), km-due-at, date-due-at, status with reason string ("overdue by km (+2,400 km vs interval)"), sorted safety-critical and overdue first. --severe switches to the severe-service column. --json for agents.
3. timeline — projects the next 24 months of services by extrapolating the odometer from annual mileage (explicit --annual-km or derived from km ÷ age), repeating recurring tasks across the window.

When to Use

• "Is my car due for a service? It's at 84,500 km."
• "The dealer says I need the 90k package — what's actually due?"
• "I mostly do short city trips — does that change the schedule?" (yes: --severe)
• "What will maintenance cost me over the next two years?"
• "I changed the oil at 63,000 km in January — when is the next one?"

Don't use for:

• Diagnosing symptoms (noises, warning lights, leaks) — that's a mechanic.
• Model-specific intervals — the library is generic; your owner's manual always overrides (see Pitfall #1).
• Warranty compliance tracking (needs dealer-documented service records).

Quick Start

# 1. See the task library
python3 scripts/car_maintenance.py tasks

# 2. What's due right now? (84,500 km, registered 2021-03-10, mostly city driving)
python3 scripts/car_maintenance.py status \
  --km 84500 --in-service 2021-03-10 --severe

# 3. Same, but you know the oil was done at 63,000 km on 2026-01-15
python3 scripts/car_maintenance.py status --km 84500 --in-service 2021-03-10 \
  --history '[{"task":"oil","km":63000,"date":"2026-01-15"}]' --severe

# 4. Budget the next 24 months (~15,000 km/yr)
python3 scripts/car_maintenance.py timeline \
  --km 84500 --in-service 2021-03-10 --annual-km 15000

# 5. Machine-readable output for agents
python3 scripts/car_maintenance.py status --km 84500 \
  --in-service 2021-03-10 --json

How It Works

Dual intervals (whichever comes first). A task is due at last_done_km + interval_km OR last_done_date + interval_months, whichever event arrives first. A 12,000 km/year car hits the oil change's 10,000 km before its 12 months; a retired driver's 4,000 km/year car hits the 12 months first. Both are "due" — mileage is a proxy for engine hours and heat cycles, time for chemistry (oil oxidation, brake fluid hygroscopy, coolant inhibitors).

Severe service. Short trips, city driving, towing, dust, and extreme heat are the manufacturer-defined "severe" conditions. --severe switches tasks to their severe intervals (oil 10,000→5,000 km; transmission fluid 100,000→60,000 km) or applies a global 0.75 multiplier where no specific value exists. Most urban commuting qualifies — this is the single most commonly missed adjustment.

Due-soon band. DUE SOON = within 20% of the km interval remaining, or within 30 days of the time deadline. Anything beyond is OK.

No-history default. Without --history, the model assumes each task was last done at in-service @ 0 km — i.e. never. On a used car with unknown history this deliberately over-reports: baseline everything cheap (fluids, filters) and move on. Feed real history entries (task, km, date) as you learn them.

Projection. timeline converts annual mileage to km-per-day and walks each task's next event forward, repeating recurring services across the 24-month window, giving each event an estimated odometer reading and cost range — the basis of a realistic maintenance budget.

Task Library (generic defaults)

Values are rounded generic conventions, not a substitute for the book for your exact model.

Workflow

1. Gather inputs: current odometer, in-service/first-registration date, any known service history (from receipts or the dealer's printout).
2. Decide severe vs normal: any of short trips <10 km, mostly stop-and-go, towing, dusty/unpaved roads, extreme heat → --severe.
3. Run status. Read OVERDUE safety-critical items first (tires, brake fluid, wipers, inspection) — those are the ones that bite.
4. Cross-check against the owner's manual; the manual wins where they differ.
5. Feed real history entries as you collect them; the report sharpens.
6. Run timeline once a year to budget; run status monthly or before trips.

Common Pitfalls

1. Trusting generic intervals over the owner's manual. Intervals vary by engine, transmission, and market. Use this tool to understand structure and challenge upselling; use the manual for the numbers.
2. Ignoring severe service. "Severe" sounds exceptional but describes most city commuting. Running normal intervals on a severe-duty car is how sludge and transmission failures happen.
3. Assuming time-based items don't matter on a low-mileage car. Oil, brake fluid, and coolant age by chemistry, not just km. A 5-year-old 30,000 km car is overdue for fluid services.
4. Reading a giant OVERDUE list as a literal work order on a used car with unknown history. It's a "baseline it" signal, not 13 simultaneous failures. Prioritize safety-critical, then fluids.
5. Accepting a dealer's bundled "package" at face value. Compare its contents against status output; items listed as OK are profit, not maintenance.
6. Forgetting units. The tool is km-based. For miles, convert first (×1.609) — mixing units silently shifts every interval.

Verification Checklist

• python3 scripts/car_maintenance.py tasks runs and prints the library
• status with your km/date prints a sorted table + summary counts
• --severe visibly shortens oil (10,000 → 5,000 km) in tasks
• --history entries shift the oil due-at km/date
• timeline covers 24 months and repeats recurring tasks
• --json output parses (meta + tasks keys)
• python3 scripts/test_car_maintenance.py → ALL TESTS PASSED

Example: reading the output

Vehicle: 84,500 km | in service 2021-03-10 | ~15,463 km/yr | SEVERE SERVICE
 ! Tire rotation          OVERDUE  safety-critical  6,000   2021-07-10
 ! Brake fluid            OVERDUE  safety-critical  30,000  2022-09-10
 ! Engine oil & filter    OVERDUE  wear-item        68,000  2026-07-15
   ...
Summary: 13 OVERDUE, 0 DUE SOON, 0 OK

The oil row reflects the history entry (63,000 km + severe 5,000 = due at 68,000, and Jan 15 + 6 mo = Jul 15 — km wins, it's already past). The tire rows show why "the car feels fine" isn't evidence: the model surfaces what the odometer and calendar already know.

One-Shot Recipes

Used-car baseline audit (unknown history, 3 years, 60,000 km):

python3 scripts/car_maintenance.py status --km 60000 \
  --in-service 2023-08-01 --severe --json

Read: safety-critical OVERDUE = do now; wear OVERDUE = baseline fluids & filters, ~$250–450 at an independent shop.

Challenge a dealer's 90k package:

python3 scripts/car_maintenance.py status --km 91000 --in-service 2019-05-02 \
  --history '[{"task":"oil","km":85000,"date":"2026-03-01"},
              {"task":"cabin_filter","km":85000,"date":"2026-03-01"},
              {"task":"tire_rotation","km":85000,"date":"2026-03-01"}]'

Anything in the package marked OK here is upsell; anything OVERDUE, price it against the cost column before agreeing.

24-month budget:

python3 scripts/car_maintenance.py timeline --km 91000 \
  --in-service 2019-05-02 --annual-km 14000 --json

Sum the cost ranges by quarter; expect roughly $500–900/yr for an aging commuter car, front-loaded if the list has OVERDUE entries.

Advisory tool. Generic intervals; your owner's manual and local law (e.g. mandatory inspection dates) always take precedence.