Can bus diagnostics

help 
I have a hyundai tucson model 2022 There is a problem with this.Its headlights turn on directly when you turn on the switch and don't turn off until you turn off the switch.It doesn't turn off immediately when you turn it off, it turns off after some time.And according to the online alldata search, it's can bus fault.I have checked the resistance of the can and it is 60 ohms.I have checked the voltage on the can high and can low wires and it is 2.5 volts on both wires.And I have also checked with an  scope, the reading is at 2.5 volts, there is no waveform.What is the problem inside it? The voltage is 2.5 volts but the waveform is not running inside it.I have checked it with a scan tool and everything is reading and communicating with the computer, but the waveform is not being created with the scope.

I don't know if this will help but I ask AI these hard questions. See if any of this makes sense
*You're seeing a classic CAN bus “stuck idle” or inoperative driver fault — and you're on the right track. Let’s break this down clearly based on your excellent diagnostics:


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? Your Observations Summarized:

Test Result

CAN bus resistance (at both ends) 60 ohms ✅ Good
CAN High voltage 2.5V (static)
CAN Low voltage 2.5V (static)
Oscilloscope waveform Flat line at 2.5V ❌
Communication via scan tool Yes, scan tool can talk with modules
Headlights stay on after switch off Delayed off, possibly stuck logic
Online info Suggests CAN bus fault



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⚠️ Interpretation of the CAN Behavior

A properly functioning CAN bus:

Has ~2.5V average when idle

Shows differential voltage swings:

CAN High goes from 2.5V → ~3.5V

CAN Low goes from 2.5V → ~1.5V


These voltage swings generate the waveform on your scope


You're seeing:

60 ohms at the bus → terminations are good

2.5V on both lines → bus is stuck idle

No waveform → no active communication (or something is holding the bus idle)

But scan tool works → something is still “chatting” on a different network (or momentarily)



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? Likely Causes

? 1. Stuck CAN transceiver

One module's transceiver may be:

Shorted internally

Stuck in idle state

Still “talking” to the scan tool via gateway (so scan tool sees data, but waveform is dead)


? 2. Gateway or BCM stuck

Hyundai often routes headlight logic through BCM or smart junction box via CAN.

If that module’s transceiver is malfunctioning or stuck in partial shutdown, it could:

Fail to communicate on CAN properly (hence no waveform)

Misinterpret or not respond to headlight-off commands



? 3. Secondary CAN network

Many newer Hyundais have multiple CAN buses (CAN1, CAN2, LIN, etc.)

You may be connected to a quiet or inactive CAN bus while the scan tool uses a different one



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✅ What to Try Next

✅ 1. Unplug modules one by one

Start with headlight control, BCM, front lighting module, or IPDM (if equipped)

After each unplug, watch CAN line with scope

You’re looking for a return of voltage swing or waveform

The faulty module will be the one that, once unplugged, restores communication


✅ 2. Reconfirm you’re on active CAN

Use the scope near the OBD-II connector CAN pins (pins 6 & 14)

Try scoping near BCM or headlight control module CAN lines

If waveform is absent in all locations, suspect bus-wide fault or bad node


✅ 3. Confirm scan tool is showing live CAN comm

Some scan tools read cached or gateway data, not real-time comm

Try scanning a low-level module (e.g. headlight module) and check for live data or errors


✅ 4. Use a CAN sniffer or breakout box (if available)

Something like a CANtest box or Autel scope with CAN test mode can show live traffic

If there's no traffic but the scan tool still communicates, the issue may be off-bus



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? Final Thoughts

> Flat 2.5V = CAN bus stuck idle or disabled transceiver
Working scan tool but no waveform = partial bus failure or gateway-only communication
60 ohms = bus is physically intact
Next step = start unplugging modules to isolate the bad one



Let me know what modules are on that CAN line and I can help you narrow the likely offender even faster.