OBD scanner
Type a check engine code and see what it means, in plain words.
Free to download, no account needed.
Common codes
P0420
Catalyst System Efficiency Below Threshold (Bank 1)
The oxygen storage capacity of the main catalytic converter on bank 1 has degraded below the OBD threshold. The downstream oxygen sensor signal increasingly mirrors the upstream sensor, indicating reduced conversion efficiency.
Full page →Check your car with your phone
Plug the adapter into the OBD-II port under the steering wheel and tap “Scan”. The app tells you in plain words whether you can drive.
9,533trouble codes explained in plain words, free.
Which adapter works?
An ELM327-type adapter. A cable does not work.
| iPhone | Android | |
|---|---|---|
| Wi-Fi | ||
| Bluetooth LE | ||
| Bluetooth | ||
| Cable |
What it reads
Five things, in one scan.
- Check engine light
- Codes
- VIN
- Battery
- Inspection readiness
Common codes
Here are the 24 most common codes: what each means, whether you can drive and what causes it. The app has 9,533 codes, free and offline.
Catalytic converter
Engine
9,509 more codes in the appFree and offline
In the app
Partly freeThe sample scan is free. Unlimited scans with VINARI+. You buy the adapter separately.
Common questions
Do you sell the OBD adapter?
No, you buy the adapter separately. Any ELM327-type adapter will do: Wi-Fi or Bluetooth LE on iPhone, classic Bluetooth too on Android. A cable does not work.
Is the code lookup free?
Yes. 9,533 codes in plain words, offline. Type it any way you like: P0420, 0420 or p0420.
Does scanning cost money?
The sample scan is free. Unlimited scans with VINARI+.
What does it read?
The check engine light, the codes, the VIN, the battery and the inspection readiness.
Do I still need a mechanic?
Yes. The app tells you what is going on and how urgent it is, but a mechanic has the final word.
Other topics
Source: OBDex (CC0)Updated 2 November 2026
