CAN, LIN, FlexRay, MOST Data Network Diagnostics & Repair

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Modern vehicles are complex electronic systems where dozens of control units operate within a single data network.

CAN, LIN, FlexRay and MOST networks are responsible for communication between the engine, transmission, safety systems, comfort modules and multimedia systems.

If communication fails – the issue can affect the entire vehicle.

Szulc Motorsport – diagnostics, not guesswork.

Communication issues between control units?

Typical symptoms:

no CAN communication
gateway faults
limp mode with no clear cause
ABS / ESP / ADAS systems not working
gearbox issues without mechanical faults
no access to control modules

In many cases, this is not a failed component.

This is a data network problem.

CAN diagnostics – basic test

The first step is checking CAN bus resistance.

Measurement is performed at the OBD port (pins 6 and 14) with ignition OFF.

Results interpretation:

~60 Ω → network OK
~120 Ω → open circuit
0 Ω → short circuit

This is a quick and effective initial check.

Advanced diagnostics – oscilloscope analysis

In real-world diagnostics, scan tools are not enough.

Oscilloscope analysis allows detection of:

signal disturbances
short circuits to ground or power
faulty control units blocking communication
transmission errors

Data rates:

CAN → up to 1 Mbit/s
FlexRay → up to 10 Mbit/s
MOST → up to 150 Mbit/s

Without signal analysis, many faults remain invisible.

CAN wiring repair – critical rules

Incorrect wiring repair leads to recurring faults.

Key principles:

maximum untwist length: ~50 mm
minimum distance between joints: ~100 mm
maintain proper twist of CAN High / CAN Low

Ignoring these rules causes signal distortion and communication errors.

Vehicle communication networks

Modern vehicles use multiple data systems:

CAN – main network
LIN – comfort systems
FlexRay – safety systems
MOST – multimedia
K-Line – legacy diagnostics
Ethernet – high-speed modern communication

Each requires a different diagnostic approach.

Most common CAN network issues

Typical real cases:

no CAN communication (Audi / VAG, BMW, Mercedes)
gateway errors
no communication with modules
random faults across multiple systems
limp mode without clear cause
ADAS system failures

In many cases, the root cause is the network itself, not the component.

When clients come to us

CAN diagnostics usually involves cases where standard diagnostics failed:

no communication despite seemingly good wiring
unexplained gateway faults
inability to connect to specific modules
intermittent communication errors
vehicle in limp mode with no mechanical issues

Most common causes of CAN failures

damaged wiring harnesses
short circuits or open circuits
faulty modules blocking communication
post-accident electrical damage
incorrect wiring repairs
retrofits and electrical modifications

That’s why proper diagnostics must be based on measurements and signal analysis, not fault codes alone.

Real-world diagnostics approach

Communication faults can:

affect multiple systems at once
be stored in a different module than the root cause
block full vehicle diagnostics
appear even when components are fully functional

Data analysis is key – not parts replacement.

Real cases

Typical scenarios:

damaged wiring after collision
control units blocking communication
faults after incorrect repairs
issues after electrical modifications

Each case requires an individual approach.

Scope

Primary focus:

Audi / VAG CAN diagnostics

Selected cases also handled for:

BMW
Mercedes
Porsche

Approach

diagnostics based on measurement and data analysis
no guessing
no unnecessary parts replacement

Szulc Motorsport – cases others failed to solve.

CAN diagnosis