Diag4You PL
iPhone app + OBD adapter

Know your car
in 4 steps

Other apps show numbers. Diag4You tells you what's going on with your car.

We'll send one message when the beta is ready. Email only, nothing else.

Read-only No account Results offline
Diag4You result screen: test passed, 2 things to check, finding card about an intake leak
How it works

Four steps, one screen

No manual, no code tables. The app takes you from plugging in the adapter to a clear result.

1

Connect

Plug the adapter into the OBD port and switch on the ignition. The app finds the adapter and recognises the car by its VIN.

2

Start

Reads fault codes from the engine, gearbox, ABS, airbags and electrics while parked.

about a minute
3

Drive, then Stop

Drive as usual. The ring counts the time, and a longer drive gives a more precise result.

at least 10 minutes
4

Analyse

Results straight away, offline: what to check and why. AI analysis and a PDF report on request.

Connect screen: step 1 of 4, Connect to adapter button
1 · ConnectOne button and a hint where the port is.
Drive screen: countdown ring, five live values, engine speed chart
3 · DriveA ring, five live values and a list of what's already checked.
Result screen with a finding worth checking
4 · ResultSystem status and findings with an explanation.
Why it sees more

It sees more than a fault code scan

An engine computer only stores a fault code once something crosses a threshold. Before that, a developing fault often shows up in the live data: the turbo can't reach target boost, the DPF builds up more and more back-pressure, fuel trims creep up. Diag4You records these parameters while you drive and assesses them with rules for your engine.

How the analysis works

Fault codesengine, gearbox, ABS, airbags, electrics
Live driving databoost, DPF, fuel trims, temperatures, ignition
Driving conditionscold and warm engine, idle, full load
On-phone analysis
  • over 400 rules for specific engines, from public sources
  • comparison with this car's earlier drives
  • assessed separately for each driving condition
Works offline.
!Turbo can't reach target boost under load

No fault code yet. First check the intake and intercooler for leaks, then the turbo actuator.

worth checking

How a fault develops

illustration
  1. 1First deviationNo warning light yet, but the drive recording already shows a change in the data.
  2. 2Fault code and warning lightThe value crosses the ECU threshold. Only now does a plain code scan see anything.
  3. 3BreakdownA repair at this stage usually costs more than at stage 1.
What gets checkedCode scanDiag4You
Fault codes stored in the control units✓✓
Live parameters while drivingboost, DPF back-pressure, fuel trims, temperatures, ignitionno✓
Assessment in different conditionscold and warm engine, idle, under loadno✓
Rules for specific enginesover 400 rules from public sourcesno✓
Comparison with the car's earlier drivesno✓
What to check first, in plain wordsno✓

Sample findings from a drive recording

sample data

Boost at full load

ECU targetactualmissing boost
Findingworth checking
Measured
0.3–0.4 bar below target from 2500 rpm
Expected
actual close to target across the range
Fault code
none yet
What to check first
  1. Intake and intercooler for leaks, e.g. a smoke test
  2. Turbo actuator and variable vanes
  3. The turbocharger itself: shaft play, oil traces
What you get

A verdict, not a table of numbers

Five systems at a glance and one sentence on what to do next

The knowledge base runs on your phone and turns codes and readings into clear findings: what to check first, which parts may be involved and what to tell the workshop.

EngineOK
GearboxOK
ABScheck
AirbagsOK
ElectricsOK
example

History and trends

Every drive is saved to the car's history. The app compares them and spots changes early, such as a rising pressure difference across the DPF.

DPF pressure difference, drive by drive

Before and after the repair

Record a drive before the workshop visit and another one after. You'll see in black and white whether the repair helped.

Before2 things to check
Afterall systems OK

PDF report for the workshop

Your mechanic gets a ready list: what to check first and why.

Before buying a used car

A 10-minute test drive with the adapter tells you what to ask the seller.

AI analysis on request

For the curious, a full write-up of the drive. Only a numeric summary is sent for analysis, never the raw file.

400+rules in the knowledge base
7brand groups
~1 minto read fault codes
10 minof driving for a full result
Brands and adapters

Which cars it works with

Knowledge of specific engines

BMWMINIVolkswagenAudiŠkodaSeatCupraPorscheToyotaLexusRenaultDaciaHyundaiKiaPeugeotCitroënDSMercedes-Benz

Mercedes-Benz uses standard OBD for now, with fewer parameters. Opel/Vauxhall and Ford are not supported yet.

Recommended adapters

Vgate vLinker MC-iOSBluetooth LE · recommended
OBDLink CXBluetooth LE

iPhone only connects to Bluetooth LE adapters. Cheap classic Bluetooth adapters won't work.

For workshops

Customers arrive with a ready report

  • Your own workshop panel. Driver requests in one place.
  • Workshop code. Drivers enter it in the app and send their recording straight to you.
  • You make the call. You tell the driver what happens next. The app suggests, the workshop decides.
Get in touch kontakt@diag4you.pl
Request from a driver2 to check
CarBMW 3 · VIN ••••••4821
Recording12 min drive · codes from 5 systems
Top findingintake leak
Workshop replyPlease come in on Tuesday at 9:00, we'll check the crankcase vent and intake.
example
Safety and privacy

It only looks, it never touches

Read-only

The app reads data from the car and changes nothing. It clears fault codes only when you explicitly ask, with the car parked.

Data stays on your phone

Your drive recordings stay with you. Results are produced on the phone without sending anything.

AI only sees numbers

When you ask for AI analysis, we send a numeric summary of the drive and the codes, not the raw file.

VIN masked in links

The VIN is masked in links shared with a workshop.

Deleted after 180 days

Recordings sent to a workshop are deleted from the server after 180 days.

The workshop decides

Diag4You suggests what to check. Whether the car is fit to drive is for a mechanic to decide.

FAQ

Frequently asked questions

Does it replace a workshop?

No. Diag4You tells you what looks suspicious and what to check first. Diagnosis and repair decisions are made by a mechanic.

Does the app clear fault codes?

Only when you explicitly ask, and only with the car parked. It never clears anything on its own.

Which adapter should I buy?

We recommend the Vgate vLinker MC-iOS or OBDLink CX. The adapter must use Bluetooth LE, as only those connect to an iPhone.

Which cars does it work with?

BMW, MINI, VW, Audi, Škoda, Seat, Cupra, Porsche, Toyota, Lexus, Renault, Dacia, Hyundai, Kia, Peugeot, Citroën and DS. Mercedes-Benz via standard OBD for now. Not yet Opel/Vauxhall or Ford.

How long does a test take?

About a minute to read codes while parked, then at least 10 minutes of normal driving. The longer you drive, the more precise the result.

Does it work offline?

Yes. Reading, driving and the knowledge-base result all work offline. You only need a connection for AI analysis and sending a report to a workshop.

Be among the first to check your car

The app is in testing. Leave your email and we'll let you know when it's ready to download.

Email only. No newsletter.