ACtion Magazine - June 2017 - 27
VW/Audi LIN-bus A/C Pressure Transducers
suring blocks may vary on different
vehicles.)
Tim Iezzi)
I found it interesting that VW is
using LIN-bus here and apparently
has been for quite a while, as that
pressure sensor fits A6 models dating
back to 2006 as well as many other
Audis and some new Golfs. Although
we don't know if cars (besides the
ones featured here) are using this type
of pressure transducer and system architecture, it makes sense that others
would operate similarly.
Figure 5: A scope capture of the LIN-bus with the engine running and the A/C turned
on, shows normal data communication.
repaired this car, but I decided to conduct some research for the next one
that comes in.
My research revealed the VESCM
supplies just over 10 volts to the sensor on Pin # 2, which the sensor then
toggles low to enable communication. Figure 5 is a scope capture of the
LIN-bus with the engine running and
the A/C turned on. We see normal data
communication occurring here, but
we do not know enough to decipher
it easily to learn what the actual pressure is. Nor can we conclude what
messages are from the pressure transducer and which ones are from the humidity sensor. Knowing that the voltage originates from the module and is
pulled low by the sensor is important
info to have when troubleshooting a
no-communication issue.
PIDs until I found one that matched
the readings on the high side gauge.
(By the way, I did not try these tests
with my SnapOn scan tool. Also, mea-
Note: Tim Iezzi is a MACS
trainer and co-owner of Iezzi's
Auto Service in Reading, PA, a
long-time MACS member service shop. At MACS 2017 in
Anaheim, CA he was the recipient of a MACS Young Ambassador Award for his outreach work
in the mobile air conditioning
industry. You can reach Tim at
macsworldwide@macsw.org
We can also view A/C pressure in
the data stream in each control module. In controller 08 (HVAC), the
pressure is in measuring block 1 field
4. In controller 09 (VESCM), it is
in measuring block 23 field 1. Neither
Autel nor Ross-Tech had the advance
measured values PID lists available
in these modules to enable me to pick
the pressure PID. I went through
all the measuring blocks looking for
June 2017 * ACTION
27
http://www.omega-usa.com
Table of Contents for the Digital Edition of ACtion Magazine - June 2017
Outlook
Service Port
Leonard's Law
Virtual View
Cooling Corner
Member Profile
Today's Technicians need to be Forensic Scientists
VQ/Audi LIN-Bus
MACS APP
Industry News
Association News
New Products
Last Watch
ACtion Magazine - June 2017 - Cover1
ACtion Magazine - June 2017 - Cover2
ACtion Magazine - June 2017 - 3
ACtion Magazine - June 2017 - 4
ACtion Magazine - June 2017 - 5
ACtion Magazine - June 2017 - Outlook
ACtion Magazine - June 2017 - 7
ACtion Magazine - June 2017 - Service Port
ACtion Magazine - June 2017 - 9
ACtion Magazine - June 2017 - Leonard's Law
ACtion Magazine - June 2017 - 11
ACtion Magazine - June 2017 - Virtual View
ACtion Magazine - June 2017 - 13
ACtion Magazine - June 2017 - Cooling Corner
ACtion Magazine - June 2017 - 15
ACtion Magazine - June 2017 - Member Profile
ACtion Magazine - June 2017 - 17
ACtion Magazine - June 2017 - Today's Technicians need to be Forensic Scientists
ACtion Magazine - June 2017 - 19
ACtion Magazine - June 2017 - 20
ACtion Magazine - June 2017 - 21
ACtion Magazine - June 2017 - 22
ACtion Magazine - June 2017 - 23
ACtion Magazine - June 2017 - VQ/Audi LIN-Bus
ACtion Magazine - June 2017 - 25
ACtion Magazine - June 2017 - 26
ACtion Magazine - June 2017 - 27
ACtion Magazine - June 2017 - 28
ACtion Magazine - June 2017 - 29
ACtion Magazine - June 2017 - MACS APP
ACtion Magazine - June 2017 - 31
ACtion Magazine - June 2017 - 32
ACtion Magazine - June 2017 - 33
ACtion Magazine - June 2017 - 34
ACtion Magazine - June 2017 - Industry News
ACtion Magazine - June 2017 - 36
ACtion Magazine - June 2017 - Association News
ACtion Magazine - June 2017 - 38
ACtion Magazine - June 2017 - 39
ACtion Magazine - June 2017 - New Products
ACtion Magazine - June 2017 - 41
ACtion Magazine - June 2017 - Last Watch
ACtion Magazine - June 2017 - Cover3
ACtion Magazine - June 2017 - Cover4
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