ACtion Magazine - June 2017 - 26

these sensors are, for all intents and purposes, modules.
See Figure 2.
On an initial scan, I found DTC 00256 (A/C Pressure/
Temperature Sensor-G395- No Signal / Communication)
set in both the HVAC module (J255, address 08 on the
scan tool) and in the VESCM (J519, address 09 on the
scan tool). In addition, I discovered DTC 00457 (VESCM
-J519- Please check DTC memory) also stored in the
HVAC module. That code description may sound odd, but
it's basically just instructing you to check for codes in
the VESCM. DTC 00256 indicates an implausible reading
from the pressure transducer, which is a fault that inhibits
compressor operation for obvious reasons.
What I think is interesting is how this sensor works.
Per the description of operation that is in service info,
the pressure transducer does not output an analog voltage signal as we would expect to see from most pressure
transducers. Rather, this pressure transducer is actually
on a LIN-bus (Local Interconnected Network) with the
VESCM. This data is then sent to the HVAC module over
the Comfort Data Bus. Also on this bus is the humidity
sensor. Both sensors are supplied power from Fuse # 3 (lo-

26

ACTION * June 2017

Figure 3: This smashed pressure sensor was replaced, along
with the broken electrical connector. Corrosion can be seen on
both components.
cated in Fuse Panel C in the
underdash fuse box) and are
grounded to the left A-pillar.
Not much information
on testing this sensor (See
Figure 4) is listed in service
info, which is expected since
Audi would rather have you
use its "guided fault finding"
methods in ODIS (Offboard
Diagnostic Information System Service, VW's diagnostic & reprogramming software) for testing.
In the case of this A5,
the repair was rather cut and
dried as I had a broken electrical connector and corrosion
on the sensor pins (Figure 3).
Replacing the electrical connector and pressure sensor

Alldata

Figure 2: Electrical diagram shows part of A5's "Climatronic"
automatic temperature control system. Shown here is the
VESCM (J519), along with Humidity (G657) and Pressure
(G395) Sensors, which share a common ground. N280 denotes the eVDC control valve.

Tim Iezzi

Alldata

VW/Audi LIN-bus A/C Pressure Transducers

Figure 4: The A/C high side
pressure sensor (Audi P/N
4H0959126B) is mounted
directly on the condenser's
liquid line connector. It fits
451 vehicle variants of 20
models produced between
2005 and 2017.



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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