Can you explain how this system works?

Michael Technician Fresno, California Posted   Latest   Edited  
2011 Lexus IS250 2.5L (4GR-FSE) 6-spd (A760H)
No Dtc's

Scoped signals at these actuators for the HVAC system and got some very weird wave forms. Looked like a mixed signal/composite signal but unsure. Has anyone diagnosed the communication from the amplifier to the actuators and understands the protocol or strategy?

Tim Curriculum Developer
San Diego, California
Tim Default

You're seeing LIN waveforms - a simple network where all actuators get the same commands, but the connectors are 'smart' and know which messages are for them. All you can do is verify power, ground, and 0-12 Volt LIN traffic at each connector (OK, it's 0-2 Volts minimum to 12-B+ maximum), as shown in the first attachment (from a '17 GM). If present, then Scan Tool PIDs and bi-directional…

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Josh Technician
Lynchburg, Virginia
Josh Default

That is a very good explanation and examples of the wave forms. Thanks for sharing that.

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Billy Mechanic
Deming, New Mexico
Billy Default

Excellent explanation Thank you

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Jim Curriculum Developer
Frederick, Maryland
Jim Default

Tim, that is a solid description. The only thing I would add to it is that on Toyota vehicles the motors and data tend to be unique to a position. One motor will have a range of (examples) 28-56 for command and position response. On a dual system you will see specs for position be 5-105 for one blend door while the other will be 4-104. The mode door will be unique as well. The sockets where the…

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