Support Center

Get help with Diagonal app, find answers to common questions, and learn how to make the most of your OBD-II diagnostics experience.

Getting Started

System Requirements

Diagonal works with:

  • iOS 17.0 or later
  • iPhone and iPad (universal app)
  • Bluetooth-enabled OBD-II adapter (ELM327 compatible)
  • Wi-Fi OBD-II adapter (optional)
  • 1996 or newer OBD-II compliant vehicle

Compatible OBD-II Adapters

Diagonal supports most ELM327-based adapters:

  • Bluetooth Low Energy (BLE) adapters
  • Wi-Fi enabled adapters
  • Popular brands: Veepeak, BAFX, OBDLink, and more
  • Both genuine ELM327 and compatible chips

First Setup

Getting started is simple:

  • Download Diagonal from the App Store
  • Plug your OBD-II adapter into your vehicle
  • Turn on your vehicle's ignition
  • Open Diagonal and follow the connection wizard
  • Start your first drive cycle analysis

Frequently Asked Questions

How does Diagonal cut drive cycle times in half? +
Diagonal uses intelligent monitoring of your vehicle's OBD-II readiness monitors and provides real-time guidance to optimize your driving patterns. Instead of driving aimlessly and hoping your monitors complete, Diagonal tells you exactly what driving conditions are needed and tracks your progress in real-time on your Lock Screen.
What is a drive cycle and why is it important? +
A drive cycle is a series of driving conditions that your vehicle's computer uses to test its emission control systems. You need to complete these cycles before passing an emissions test or smog check. Diagonal helps you complete these cycles efficiently on the first try.
Can I use Diagonal without an OBD-II adapter? +
While Diagonal offers some features without an adapter (like trouble code lookup and general automotive guidance), you need a Bluetooth or Wi-Fi OBD-II adapter to access real-time diagnostics, drive cycle tracking, and live monitoring features.
Is my vehicle data secure? +
Yes. All diagnostic data is encrypted and stored securely. We never sell your data to third parties. Your vehicle information is used solely to provide you with accurate diagnostics and improve the app experience.
What's included in the subscription? +
The Diagonal Pro subscription includes unlimited AI mechanic consultations, advanced Mode 6 diagnostics, cloud sync across devices, export capabilities, and priority customer support. Basic OBD-II reading and drive cycle tracking remain free.
My OBD-II adapter won't connect. What should I do? +
First, ensure your vehicle's ignition is on and the adapter is fully inserted. Check that Bluetooth is enabled on your device. If using a Wi-Fi adapter, connect to its network first. Try restarting both your phone and vehicle. If issues persist, contact our support team.
Does Diagonal work with hybrid or electric vehicles? +
Yes, Diagonal works with hybrid vehicles that have traditional OBD-II ports (1996+). For fully electric vehicles, functionality may be limited as they don't have the same emission control systems that require drive cycles.

Troubleshooting

Connection Issues

  • Ensure your vehicle's ignition is on
  • Check that the OBD-II adapter is fully inserted
  • Verify Bluetooth is enabled on your device
  • Make sure you're within range (typically 30 feet)
  • Try restarting both your phone and vehicle
  • Check adapter compatibility with your vehicle

Drive Cycle Not Completing

  • Follow the in-app driving instructions exactly
  • Ensure your vehicle is fully warmed up
  • Don't turn off your engine during the cycle
  • Some monitors require specific driving conditions
  • City and highway driving may both be required
  • Allow sufficient time for each phase

App Performance

  • Ensure you have the latest version from App Store
  • Restart the app completely
  • Check available storage space on device
  • Close other apps to free up memory
  • Ensure stable internet connection for AI features
  • Try logging out and back in to refresh sync

Still Need Help?

Our support team is here to help you get the most out of Diagonal. We typically respond within 24 hours.

support@drivecycle.app

When contacting support, please include:

  • Your device model and iOS version
  • Diagonal app version
  • OBD-II adapter brand and model
  • Vehicle make, model, and year
  • Detailed description of the issue
  • Screenshots if applicable