RealDash loses connection to USB-CAN Analyzer when engine starts (works fine with ignition only)

General
1

Hey everyone,
I’m running RealDash on an Android head unit and using the Seeed USB-CAN Analyzer to read CAN data from my ECU.

When I turn the ignition switch ON (engine off), everything works perfectly — RealDash connects to the adapter and reads all the CAN data correctly.
However, as soon as I start the engine, RealDash immediately loses connection to the USB-CAN Analyzer.

Here are some details about my setup:

  • Android screen/head unit running RealDash (latest version)
  • Seeed Studio USB-CAN Analyzer (non-isolated version)
  • CAN wiring: CAN-H, CAN-L, and GND connected directly to the ECU
  • Power for the analyzer comes from the Android head unit’s USB port
  • The same CAN bus setup works perfectly with my Raspberry Pi + CAN HAT, even with the engine running

It seems that when the engine starts, the USB-CAN analyzer disconnects — possibly due to a ground or voltage issue, since it’s powered and grounded through the ECU and Android USB at the same time.

Has anyone experienced similar behavior?
Would isolating the CAN ground or using a USB isolator between the Android unit and the CAN analyzer fix this?
Or is there a more stable way to power or ground the analyzer in a car setup?

Any advice or known fixes would be really appreciated.

Thanks!

2

Hi. In many cars, when the starter is running, the voltage at one of the contacts of the ignition terminal disappears. Perhaps your device is powered by just such a contact. You should find the ignition wire that does not disappear while scrolling.

3

This is the can device disconnecting or are you losing the can signal?

4

The Android unit turns off when you start the car?

5

I’m losing the can signal

6

That’s a good point — thanks for mentioning it. But in my case, the Android unit is powered through the radio harness, so it shouldn’t be losing power during cranking.

7

No it doesn’t, I only lose can signal

8

With everything off, measure the resistance across can hi and Lo. You should see between 50 and 60 ohms