Peugeot 208
A practical 208 diagnostic flow (UK/EU): start with trims + misfire counters, confirm air leaks and ignition health, then move to sensor plausibility. Don’t guess parts.
Quick triage (what to capture)
Minimum data
- Codes + freeze-frame
- STFT/LTFT at idle and at ~2,000 rpm
- Misfire counters (if available)
- MAP (kPa) / MAF (g/s) at idle + light cruise
- Lambda/O2 behaviour during a steady cruise
Fast interpretation
- Lean at idle only → intake/PCV leak, brake servo line, vacuum plumbing.
- Lean under load → fuel delivery, air metering bias, or boost/charge leak (turbo).
- Misfire with normal trims → ignition or mechanical (compression, valve sealing).
- P0420 after misfires → fix misfire/trim first; cat is rarely the first failure.
Known 208 patterns (the ones that waste time if you ignore them)
- PureTech petrol (timing belt in oil, where fitted): maintenance history matters. A deteriorating belt can shed material that restricts oil pickup, creating low-oil-pressure events and secondary faults. Don’t diagnose “random warnings” without confirming the basics.
- Intermittent hesitation / flat spot: treat this as mixture control first. Check trims, intake leaks, and MAP/MAF plausibility before condemning a turbo or high-pressure pump.
- Cold-start roughness: often a mixture/air leak or ignition marginality. Verify stable lambda control and coolant temp behaviour (thermostat stuck open can keep it in enrichment longer).
- EVAP / purge behaviour: can present as long crank after refuel, rough idle, or random misfire-like symptoms. Prove vapour control before replacing coils repeatedly.
What NOT to do (high-confidence traps)
- Don’t replace a catalytic converter for P0420 unless trims and misfire behaviour are stable and the upstream sensor is proven healthy.
- Don’t shotgun ignition parts without checking which cylinder is actually misfiring and whether the ECU is correcting mixture heavily.
- Don’t ignore basic service items (oil grade, plugs, air filter). On small turbo engines, “minor” basics create major drivability complaints.
Typical OBD2 codes that show up
P0171
Lean Bank 1: trims-first plan that stops guessing.
P0300
Random misfire: separate ignition/mechanical from mixture.
P0420
Catalyst efficiency: upstream causes that mimic a bad cat.
P0299
Underboost: confirm leak vs control vs sensor bias.
Tests that confirm the cause (no guesswork)
If trims are positive at idle: smoke test the intake/vacuum plumbing. Fix the leak before touching sensors.
If trims go positive under load: check fuel pressure under load (where supported), confirm MAP/MAF plausibility, and pressure-test the charge system on turbo models.
If misfire is cylinder-specific: inspect plugs (gap/condition), swap coil/injector positions (one at a time) to see if the misfire follows, then consider compression/leakdown if it doesn’t.
Trust note: These profiles are designed to narrow possibilities. Confirm with test data (trims, misfire counters, pressure/smoke tests, voltage checks) before buying parts.