CASE STUDY: AUDI AIR CONDITIONING FAULT

Affected vehicles: Audi A3, A4, A6 2008 – 2013

Autologic says AutologicLive is an invaluable technical support resource uniquely designed to empower technicians to repair vehicles with confidence.
Through its dedicated team of OEM-Trained Master Technicians, Autologic explains it is able to provide brand-specific diagnostic support to technicians and workshop owners all over the world.
As testament to this, Autologic provides the following information as an example of the guidance provided via AutologicLive in response to a customer support request.

Symptoms Provided:
1. Air conditioning does not work
2. Local data bus fault
3. Possible battery drain
4. Non-start

Affected Vehicles
Audi A3 (2008 – 2013), Audi A4 (2008 – 2013) and Audi A6 (2008 – 2013)

Faults codes presented
• 256 refrigerant pressure sensor/temperature sensor G395 (08) A/C electronics
• 3278 function impairment due to missing message (09) Central electrics ECU

Additional Information:
Faults in central electrics (09) ‘sender for refrigerant pressure/temperature – implausible signal’ and Air conditioning (08) restricted function because of error value – no signal/communication.

Cause identification
In most cases the refrigerant pressure/temperature sensor G395/G805 is faulty, but in some cases there is a wiring issue with the LIN (signal feedback) wire which breaks/corrodes in the loom on near the inner front wheel arch.

Repair steps provided by Autologic’s OEM-Trained Master Technician
1. If the pressure sensor G395 has been replaced already and faults are still present, check part number of sensor and software of A/C electronics. If a part number 4H0 959 126 is fitted and a software level/version 050 is present, the A/C control unit will require an update to level/version 060
2. Find the air conditioning pressure sensor which is found attached to the side of the condensor behind the front grille. The three pin connector will consist of a Power (battery voltage), an earth and a signal (LIN). This can only be accurately tested with an oscilloscope. If the power and earth are ok, try to plug in a substitute sensor, or new. Make sure the faults disappear and pressure reading comes back in live data.
3. If there is still a fault then there will be a wiring fault with the LIN bus wire.
Tools Required Multi Meter
Parts Required G395/G805 A/C pressure/Temperature sensor

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