The DPF has reached end of ash life — can't be regenerated any further.
P242F — also written P242F, P 242F, 242F — is the OBD-II code for diesel particulate filter restriction — ash accumulation. Same code, same fix: this page covers every spelling of it.
Diesel Particulate Filter (DPF) ash accumulation limit reached — the ECU has calculated that the DPF is now full of unburnable ash residue (not soot) and regeneration will no longer clear it. Soot burns off during a regen; ash is the leftover metallic residue from engine oil additives and it never leaves the filter until you physically clean or replace it. P242F is not a sensor fault — it's the ECU telling you that repeated regens have not brought the differential pressure back down, and the DPF is genuinely at end of service life. On UK diesels this typically arrives between 90,000 and 140,000 miles depending on how the car has been driven and what oil has been used. A cheap garage will condemn the DPF as scrap and quote £1,800 for a new one. Bob's rule: a professional forced clean (Ceramex, TerraClean or JLM-machine 4-hour bake) restores 95%+ of P242F DPFs to full spec for £280–£450 — a fraction of replacement.
P242F is a emissions fault code, typically costing £400–£1800 to put right in a UK garage.
What P242F actually feels like to drive
- DPF warning light on the dash steady (not flashing) — often accompanied by 'Engine System Fault, Service Now'
- Reduced Engine Power warning / limp mode after another attempted regen
- Car has done multiple 'passive regens' recently (higher revs at motorway cruise, warm smell like burning) that ended incomplete
- MPG dropped 5–12 mpg over recent months as the DPF partially blocked
- Slight loss of turbo response and top-end power, engine feels 'flat'
- Sometimes stored alongside P2002 (DPF efficiency), P2452 (DPF pressure sensor), P244A (differential pressure too low), or P1471 (Peugeot / Citroën DPF)
- Exhaust smells 'hot' or 'sulphurous' after a long drive — sign of forced-regen attempts
What causes P242F?
- High-mileage DPF at ash limit
UK vehicles that throw P242F most often
- Ford Focus / Mondeo / S-Max / Kuga 2.0 TDCi (2010–2019) — very common P242F at 100k–130k
- Vauxhall Astra J / Insignia / Zafira C 2.0 CDTi (A20DTH / A20DTJ) — DPF ash saturation pattern
- BMW 1 / 3 / 5 Series 2.0d N47 & 3.0d N57 — DPF ash + partially blocked from short-trip city use
- VW Golf / Passat / Audi A3 / A4 / A6 2.0 TDI CR (CAGA / CBAB / CGLC) — high-mileage DPF saturation
- Mercedes C220 / E220 / GLC 220d (OM651 / OM654) — ash saturation past 100k, especially taxi / rep-mileage cars
- Nissan Qashqai / X-Trail 1.6 & 2.0 dCi (M9R / R9M) — DPF ash + Renault-derived issues
- Land Rover Discovery Sport / Evoque / Freelander 2 2.2 TD4 & 2.0 TD4 (Ingenium & Ford-shared) — chronic DPF issues in short-trip use
- Volvo V40 / V60 / XC60 D2 / D3 / D4 — DPF ash saturation on urban-use cars
- Peugeot 3008 / 5008 / 508 / Citroën C4 / C5 2.0 HDi (DW10) — EOLYS-fluid-consuming DPF, common P242F
How P242F is fixed
- Replace or professionally clean DPF
The P242F misdiagnosis that wastes money
P242F is the code where UK diesel owners get quoted £1,400 – £2,400 for a brand new OE DPF when a £280 – £450 professional forced clean would have restored the filter to full spec. Bob's 32 years on the tools rule for P242F: NEVER authorise DPF replacement until three things have been done. One — a professional off-vehicle DPF clean (Ceramex Cerachem, TerraClean DPF machine, JLM 4-hour bake, or DPF Doctor process). These processes reverse-flush the filter with a proprietary chemical + heated air cycle and restore around 95% of ash-saturated DPFs to within OE spec, backed by a before/after weight report and a printed pressure test. Two — a full oil and filter service with the correct LOW-SAPS oil (ACEA C1, C2, C3 or C4 depending on your car — Ford spec WSS-M2C934-B, VW 507.00, BMW LL-04). Using the wrong oil is the number one cause of premature DPF ash saturation. Three — a proper diagnostic 'DPF adaptation reset' on a scan tool with manufacturer-level DPF coverage — the ECU has an ash-mileage counter and if you clean the DPF without resetting the counter, the light will return in weeks even though the filter is spotless. Second common miss: 'DPF delete' as an easy fix. NEVER — a physically or software-deleted DPF is a guaranteed MOT failure since 2014, a £1,000 fine if caught, and voids insurance. Third miss: fitting a £180 unbranded eBay 'universal' DPF. The OE substrate specification, cell density and catalyst loading are critical — cheap replacements block again within 5,000 miles and don't pass the OBD DPF-efficiency self-test.
What a UK garage should charge for P242F
UK independent garage: DPF differential pressure test + soot / ash percentage read on scan tool £45–£80 (essential — tells you clean-vs-replace). Professional off-vehicle DPF forced clean (Ceramex, TerraClean, JLM 4-hour bake, DPF Doctor) £280–£450 including remove/refit + before/after report. Full 'DPF service' bundle — clean + oil + filter + adaptation reset £380–£550. On-car DPF chemical soak + forced regen (less effective, only worth trying on lightly-loaded filters) £120–£200. Replacement DPF fitted with genuine or top-quality aftermarket (Klarius, BM Cats, Eminox — with UK MOT paperwork) £800–£1,400. Genuine OE DPF (Ford, VW, BMW, Mercedes) £1,400–£2,800 fitted. Peugeot / Citroën cars: also budget £45–£90 for a top-up of EOLYS DPF fluid at the same time (Infineum DPX42, sold under Peugeot part number 9979A9). Main dealer: 40–70% more. Never accept DPF replacement without a written soot-and-ash percentage read AND a documented forced-clean attempt first — that paperwork is your evidence if the light returns.
P242F repair cost in the UK
Most P242F repairs land between £400–£1800 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P242F
Bob's real workshop rule for P242F: before you spend a penny on DPF work, drive the car for 45 minutes on a dual carriageway at 60+ mph, 2,500–3,000 RPM in a lower gear than usual (4th or 5th on a manual, S mode on an auto) with the heater on full to load the alternator. If the DPF is only partially loaded, a proper hot motorway run will trigger a passive regen and clear the light without a garage bill. If the light returns within a week, book the professional clean — do NOT keep driving with the DPF light on because each failed regen dumps unburnt fuel into the engine oil, thins the lubricant, and can wreck the turbo (a £900 job on top of the DPF). Second rule: only ever use genuine LOW-SAPS oil at every service (ask specifically — many garages default to standard oil to save 30p and it kills DPFs). Third: if you drive mostly short trips (under 15 minutes), a diesel is the wrong car for you — swap to petrol or hybrid, or budget for DPF service every 2 years. Fourth, on Peugeot / Citroën 2.0 HDi with the EOLYS DPF additive tank: check the fluid level at every service — an empty EOLYS tank means the DPF can't reach regen temperature and P242F becomes inevitable. Fifth, on any Ford TDCi with P242F check the exhaust flexi-pipe for cracks — a leak upstream of the DPF pressure sensor throws off the reading and stores false ash-load faults. And finally: if the garage says 'DPF has to come off and go in the bin', get a second opinion before you pay. A specialist DPF cleaning service (Ceramex, DPF Doctor UK, TerraClean centres) will honestly assess whether cleaning will work — most DPFs under 150,000 miles clean successfully. Not sure whether yours is clean-worthy or replace-only? <a href="/ask-a-mechanic-uk?code=P242F">Ask Bob about your P242F</a> for £14.99 with make, model, mileage, any paired codes and (if you have it) the soot/ash percentage from a scan tool — you'll get a straight answer before you spend £1,500 on a filter you didn't need.
Can you drive with P242F?
Limp mode, forced replacement.
Urgency: high.