Limp mode on the motorway. A misfire that only happens cold. A light that comes back every three weeks no matter how often it's cleared. These are the faults that embarrass quick-scan garages — and they're our favourite work. Root-cause investigation on live data, from £40, finished only when the why is found.
"We replaced the sensor and the light came back" is a £180 way of learning the sensor was fine.
The parts cannon is the most expensive tool in the industry. A code mentions a sensor, the sensor gets replaced, the light returns — because the code described where the symptom was measured, not where the problem lives. An underboost code blamed on a MAP sensor can be a split hose; a misfire pinned on coils can be a breather leaning out one cylinder. Every part fitted on a hunch is money spent narrowing nothing down.
Fault finding inverts that. Start with the full picture — every module scanned, every stored code mapped onto a timeline with its freeze-frame conditions. Form a hypothesis. Then test it against the running car: live data while it idles, revs and drives; actuator commands to prove components respond; wiring and connector checks where the data points. The fault gets cornered by evidence until only one explanation survives. That's the one you pay for — not the first plausible suspect.
Intermittents — the faults that vanish at the garage door — get special respect here. Freeze-frame forensics, logged drive cycles, and where needed the car instrumented to catch the fault in the act over days rather than minutes. And codes are cleared properly: after the cause is confirmed, so the system relearns from a clean slate, with adaptations reset where the repair demands it. Clearing first and hoping is how the same fault gets diagnosed twice.
Six categories that fill the diary — tap each for how the hunt works.
The ECU is protecting the engine from something specific — we find out what, not just reset it.
Limp mode is a decision, and the freeze-frame records why it was taken: overboost, EGT spike, rail-pressure sag, DPF load. Tracing that trigger finds the real fault — resetting without reading it just schedules the next limp event, usually somewhere less convenient.
Per-cylinder misfire counters and fuelling data separate coil, injector, compression and breather causes.
The misfire counters tell a story: one cylinder always, or random across all? Cold only, or load only? Each pattern indicts a different culprit — the data picks the part, which is precisely why we don't fit parts to find out.
Requested versus actual boost, logged under load, corners the leak, actuator or sensor responsible.
"It's lost its go" has a signature: target boost against measured boost across the rev range. A gap that grows with load is a leak; a lazy rise is actuation; an impossible reading is a sensor. One logged pull usually names the suspect — then we prove it physically.
Random warning lights, phantom drains, modules dropping offline — network-level detective work.
Modern cars are networks, and one corroded connector can make five innocent modules log errors. We read the pattern — which modules, which bus, what conditions — and trace it to the physical cause: the chafed loom, the damp plug, the dying battery that started the whole story.
Regeneration histories, soot models and NOx data read properly before any expensive conclusions.
Emissions lights cause the most overpriced guesswork in the trade. The data shows whether a DPF is genuinely full or just mis-modelled, whether an EGR is stuck or sooted, whether AdBlue faults are fluid, sensor or pump. Diagnosis first keeps four-figure parts bills honest — see our dedicated DPF and AdBlue pages for the fix side.
Codes cleared correctly, adaptations reset, then re-tested — so "fixed" is a measurement, not a hope.
After any repair — ours or yours — the system needs a clean slate: codes cleared in the right order, relevant adaptations reset, then a drive cycle to confirm nothing returns. The fault is closed when the data says so, and the report records it.
Watch how a session sweeps the car's systems and corners a fault — then tell us what yours is doing.
| Approach | Method | Typical outcome |
|---|---|---|
| Parts cannon | Replace what the code mentions | £100s spent, fault often remains |
| Clear & hope | Wipe codes, wait | Fault returns, evidence destroyed |
| FLR investigation | Scan → hypothesis → live-data proof | Root cause named, fix quoted |
From symptom interview to proven cause — the sequence every investigation follows.
What we tell every customer before the hunt begins.
A fault that appears once a fortnight won't always perform on command. Honest investigation sometimes means instrumenting the car and waiting for the evidence.
You'll know after session one exactly what was ruled out, what the leading suspect is, and what catching it red-handed will take. Scope and cost stay agreed before each step — no open-ended meters running.
Sometimes the root cause is a failing DPF, a tired clutch pack or an engine wearing out — news no amount of diagnostic skill can soften.
You get the truth with the evidence attached, the realistic options priced, and zero pressure toward the biggest one. Bad news delivered straight is still cheaper than good news invented.
Wiping a fault before an MOT or a sale doesn't fix anything — it hides evidence from the next owner of the problem, who might be you again in three weeks.
Codes get cleared when causes are fixed or as documented test steps. If you're selling, we'd rather help you fix and prove it — the report adds more value than the blank dashboard.
The more symptom detail you give us, the faster the hunt: when it happens, how often, what it feels like — every clue shortens the bill.
Usually because the previous attempts replaced parts instead of testing hypotheses. We start from the full evidence — every module's codes, freeze-frames, the history of what's been changed — which means previous failed repairs actually help us by ruling things out. Stubborn faults are a method problem, not a mystery problem, and root-cause method is the whole service.
Intermittents rarely need to perform live: stored codes and freeze-frame data are a recording of the last episodes, and pattern analysis across them often identifies the cause directly. When it genuinely needs catching in the act, we instrument the car to log the relevant channels over days and you drive normally until it strikes. The fault chooses when; the logger never blinks.
£40 covers the standard investigation — scan, code mapping, live-data testing and the written finding — which resolves the majority of cases in one session. Faults needing extended logging, significant dismantling or specialist rigs are quoted before we go there, never after. You approve each step's cost in advance; the meter never runs silently.
Both, usually. Software faults, sensors, wiring repairs, boost-system fixes and most common causes are work we do — quoted, never assumed. Where the cause belongs at a specialist (internal gearbox work, bodyshop territory), the report hands them a head start that typically saves you their first diagnostic hour. Either way, the finding is yours to use anywhere.
Not if the fault is live — readiness monitors reset when codes clear, and the system flags itself as not-ready until drive cycles complete, which testers check for precisely this reason. The honest route is fix, clear, complete the drive cycle, then test: a sequence we can do properly. Clearing codes to sneak a pass isn't a service we offer; fixing the cause is.
Not for us — we read calibrations for a living. We can tell whether a symptom is hardware, factory software or the tune itself, which is genuinely useful when another company's map is in the mix. If the calibration is the culprit, we'll show you the evidence and the options: correct it, replace it with one of ours, or return the car to stock from your original file if we hold it.
No symptoms, just want the full health picture? The all-module scan with written report.
£40 See diagnostics // Emissions sagas DPF SolutionsRegeneration problems and soot-load mysteries — assessed on data before anyone mentions four figures.
From £80 See DPF help // Bad-map rescue Custom / Dyno TuningWhen the fault turns out to be another tuner's file — calibration repaired or rebuilt on logged data.
From £350 See custom tuningRoot-cause investigation from £40 — evidence-led, explained in plain English, documented in writing. Bring us the fault everyone else gave up on.