MINI Cooper (Hatch)
Cooper diagnosis done the calm way: treat drivability as air/fuel control + plausibility first, then prove the cause with a short data log. Avoid guessing at sensors or turbos without confirming with trims and basic tests.
Quick triage (capture this first)
Minimum data
- Codes + freeze-frame
- STFT/LTFT at idle and ~2,000 rpm (petrol)
- MAF (g/s) and/or MAP (kPa) at idle + steady cruise
- Boost request vs boost actual (turbo models)
- Purge command vs purge actual (or purge duty cycle), note if trims improve when purge is disabled
Fast interpretation
- Lean at idle only (petrol) → intake/PCV leak, vacuum plumbing, purge stuck open.
- Lean under load → fuel delivery limitation, charge leak, or metering bias.
- Underboost → confirm leak vs control (wastegate/VGT) vs sensor plausibility.
- EVAP leak codes → smoke test and confirm purge/seal behaviour before replacing parts.
Known Cooper patterns (common time-wasters)
- Rough idle + lean trims: treat as intake/PCV leak or purge influence first. Smoke test and verify purge sealing before sensors.
- Hesitation on light throttle: often mixture control or boost control plausibility. Use trims and boost request vs actual to split leak vs control vs torque reduction.
- Cooling plausibility: if warm-up is slow or temps are unstable, fix that first. It can cascade into fueling and “performance” complaints.
- Multiple warnings at once: do a voltage/charging sanity check. Low voltage can trigger cascading module complaints that look unrelated.
Typical OBD2 codes that show up
P0171
Lean: trims-first plan that stops guessing.
P0300
Random misfire: split ignition vs mixture vs fueling.
P0299
Underboost: confirm leak vs control vs sensor bias.
P0456
EVAP small leak: confirm seal and smoke test.
Tests that confirm the cause (no guessing)
Underboost: smoke/pressure-test the charge path, then compare boost request vs actual. If request is low, look for torque-reduction causes rather than a turbo failure.
Lean trims: smoke test intake/PCV, verify purge isn't stuck open, and confirm trims at idle vs cruise. Fix air leaks/purge influence before sensors.
Misfire: use misfire counters and load data. If trims are normal and one cylinder dominates, then prove coil/plug/injector vs compression with a targeted swap test.
Trust note: These profiles are designed to narrow possibilities. Confirm with test data (trims, misfire counters, pressure/smoke tests, voltage checks) before buying parts.