LIN / Communication network

LOCAL INTERCONNECT NETWORK

Doors, seats, mirrors, climate actuators, alternators and smart sensors

NETWORK GUIDE03/14

TOPOLOGYSingle leader with multiple followers on one wire

PHYSICALSingle wire pulled toward battery voltage; dominant state is low

DATA RATEUp to 20 kbit/s in normal LIN operation

Correct theory and operation

HOW LIN
COMMUNICATES.

Understand the normal architecture, signaling and message rules before deciding that a voltage or waveform is incorrect.

Leader-controlled bus

One leader controls when communication occurs. It sends every frame header, including a break, synchronization byte and protected identifier. Followers do not arbitrate or transmit spontaneously; they respond only when the schedule and identifier call for their data.

Physical signaling

The single LIN wire is referenced to vehicle ground and pulled toward system voltage for the recessive state. Any transmitting node pulls it low for a dominant bit. The protected slew rate reduces emissions, which gives LIN its characteristically rounded edges.

Frame response

After the leader's header, the assigned publisher supplies one to eight data bytes and a checksum. Other followers listen as subscribers. Depending on the frame, the publisher may be the leader or a follower.

Scheduling and bandwidth

The leader executes a defined schedule table rather than allowing arbitration. This predictable low-cost arrangement suits mirrors, seats, flap motors, smart alternators and simple sensors, but its normal data rate is limited to 20 kbit/s.

Wake and sleep

Nodes can enter a low-current sleep state after a sleep command or timeout. A dominant wake-up pulse requests activity; the leader must then resume valid headers. A powered follower on a silent bus cannot create ordinary scheduled traffic by itself.

Common mistakes

AVOID THE
FALSE CLUE.

Testing with the connector unplugged when the fault only appears under load.
Using a generic voltage value instead of the vehicle-specific specification.
Skipping power, ground and reference checks before condemning the component.
Moving the harness or clearing codes before capturing the original evidence.
Replacing a part without repeating the test.

Reading the signal

Good waveform / normal communication

A LIN master initiates communication and the identified devices respond in their scheduled slots. The single-wire signal returns toward its pull-up supply when recessive and is driven low for dominant bits; use the actual supply and transceiver specifications.

Faulty waveform / fault indications

A stuck level, weak pull-up, missing response or distorted timing can indicate supply, wiring or node problems. An idle bus may simply be asleep. Confirm a valid wake-up and master request before treating silence as a fault.

COMPLETE TEST SEQUENCE

Verify battery supply and ground at the leader and affected follower.
Measure LIN idle voltage and check for a line stuck near zero or supply.
Scope the wake-up and message traffic at the leader, then at the follower.
Check whether the leader is sending headers before blaming a silent follower.
Disconnect followers one at a time only where the service procedure allows.
Inspect shared power, ground and LIN splices for the affected group.

⚠ SAFETY / TEST CAUTION

LIN voltage follows system voltage. Do not expect a fixed 5 V digital signal on the vehicle-side bus wire.

TEST EQUIPMENT

Wiring diagramOscilloscopeDigital multimeterScan tool with LIN data

KNOWN-GOOD BASELINE

✓ Recessive bus level follows battery supply through the pull-up network.✓ Dominant bits pull the bus low.✓ The leader schedules communication; a silent leader means followers do not speak.

COMMON FAULTS

— Bus stuck dominant low— Open pull-up or leader power loss— Follower shorting the single wire— No leader header— Voltage drop in module ground— Wake-up/sleep fault

IDENTIFY BEFORE YOU MEASURE

Confirm the network, topology, awake state and test conditions from vehicle-specific information.

NEXT NETWORK / FLEXRAYFlexRay→