Adapter guide

Which OBD-II adapter works with Regen Monitor

Two requirements

1. Bluetooth LE, not Bluetooth Classic

An iPhone can only use Bluetooth LE adapters (or Wi-Fi ones, which Regen Monitor doesn't support). Many cheap "Bluetooth OBD2" adapters are Bluetooth Classic: they pair with Android phones but never appear on an iPhone at all. If the listing only mentions Android, it's almost certainly Classic.

2. 29-bit CAN with custom flow control

The engine computer on a 2020+ Duramax answers regen questions on 29-bit (extended) CAN, not the 11-bit addresses ordinary code readers use. The adapter has to switch to 29-bit addressing and handle the multi-frame replies. Genuine ELM327-compatible chips with full AT command support can; most clones claim to and don't.

Adapters

Adapter	Bluetooth LE	29-bit + flow control
OBDLink CX	Yes	Yes
Vgate iCar Pro BLE 4.0	Yes	Usually
Unbranded "ELM327 Bluetooth" clones	Often not	Often not

OBDLink MX+ won't work: it's a good adapter, but it connects to iPhones over Bluetooth Classic through Apple's accessory program, not Bluetooth LE, so it never shows up in Regen Monitor. Choose the OBDLink CX instead.

Based on each adapter's published command support. Regen Monitor hasn't run every adapter through every truck yet; that's why the free check exists.

The free check is the real test. Before you pay, Regen Monitor walks through four steps: the adapter answers, the truck answers, the truck is identified from its VIN, and the diesel engine computer answers. If the last step fails, the adapter can't reach it, and the app will say so.

Leaving it plugged in

Regen Monitor stays connected while you drive and reconnects by itself when you start the truck again. An adapter that sleeps on its own when the truck is off (OBDLink CX does) won't drain the battery if you leave it plugged in. If yours doesn't sleep, unplug it when the truck sits for days.

Problems

The adapter doesn't show up

It's probably Bluetooth Classic. Also check that Bluetooth is on and Regen Monitor is allowed to use it (Settings → Regen Monitor → Bluetooth). Don't pair it in iOS Settings; pick it inside the app.

"Engine computer didn't answer"

The adapter talks to the truck but can't reach the Duramax's engine computer: it doesn't do 29-bit CAN properly, or the truck isn't a supported Duramax. See supported trucks.

"The truck isn't answering"

Start the engine (or switch the ignition on) and push the adapter fully into the port under the dash, left of the steering column.