Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSAUDI1999A6 BASEREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE MECHANICALCOOLING FANON BOARD DIAGNOSTIC (OBD) - HVAC
1999 Audi A6 Base
On Board Diagnostic (OBD) - HVAC
1999 Audi A6 BaseSECTION On Board Diagnostic (OBD) - HVAC
- A/C system, On Board Diagnostic (OBD)
- On Board Diagnostic (OBD), initiating
- Check DTC Memory (function 02)
- Diagnostic Trouble Code (DTC) table
- Output Diagnostic Test Mode (DTM)
- Basic Setting (function 04)
- Erase DTC Memory (function 05) and End Output (function 06)
- A/C Control Head -E87-, coding
- Read Measuring Value Block (function 08)
- Notes
- Initiating "Read Measuring Value Block" function 08
- Read measuring value blocks (vehicles up to model year 2001)
- Notes
- Display group 001: Compressor cut-off conditions, voltage for A/C clutch and at terminal 15
- Display group 002: Actuator for temperature flap left -V158-
- Display group 003: Actuator for temperature flap right -V159-
- Display group 004: Central Air Flap Motor -V70-
- Display group 005: Defroster Flap Motor -V107-
- Display group 006: Air Flow Flap Motor -V71-
- Display group 007: Calculated ambient temperature for outside air temperature display -G106-, measured values from fresh air intake duct temperature sensor -G89- and outside air temperature sensor -G17- and calculated coolant temperature
- Display group 008: Left vent temperature sensor -G150-, right vent temperature sensor -G151-, Sensor for outlet temperature, floor outlet -G192- and Instrument Panel Interior Temperature Sensor -G56-
- Display group 009: (Voltage at fresh air blower -V2-, voltage at terminal 58d and terminal 58s)
- Display group 010: (Engine speed (RPM), compressor speed, vehicle speed, auxiliary heater, and additional heater on/off) on/off)
- Display group 011: (Coolant temperature transmitted by instrument cluster, air conditioner compressor cut-in and A/C pressure switch - F129-)
- Display group 012: (Sunlight photo sensor -G107-)
- Display group 013: Last four compressor cut-off conditions
- Measuring value blocks (vehicles from model year 2002)
- Measuring value blocks from display group 001 up to display group 010
- Display group 001: A/C Compressor Regulator Valve -N280-, A/C Clutch Relay -J44- and High Pressure Sensor -G65-
- Display group 002: Last four compressor cut-off conditions
- Display group 003: Actuator for temperature flap left -V158-
- Display group 004: Actuator for temperature flap right -V159-
- Display group 005: Defroster Flap Motor -V107-
- Display group 006: Central Air Flap Motor -V70-
- Display group 007: Recirculation Flap Motor -V113
- Display group 008: Air Flow Flap Motor -V71-
- Display group 009: Measuring values Sensor for outlet temperature, floor outlet -G192-, Left Vent Temperature Sensor -G150- and Right Vent Temperature Sensor -G151-
- Display group 010: Measuring values for Evaporator Vent Temperature Sensor -G263-, Fresh Air Intake Duct Temperature Sensor -G89-, Outside Air Temperature Sensor -G17- and calculated outside temperature transmitted to instrument cluster
- Measuring value blocks from display group 011 up to display group 020
- Display group 011: Measuring value of Instrument Panel Interior Temperature Sensor -G56-, the measured RPM of Interior Temperature Sensor Fan -V42-, coolant temperature transmitted by instrument cluster and output activation for idle air control increase
- Display group 012: The current engine speed and vehicle speed transmitted from the instrument cluster, condition and value of compressor torque transmitted to the instrument cluster
- Display group 013: From instrument cluster transmitted voltage on terminal 58d and voltage on terminal 58s actual and specified voltage to activate the Fresh Air Blower -V2
- Display group 014: Coolant fan -V7- activation
- Display group 015: Activation for recirculation/fresh air mode and signal from Sensor for air quality -G238-
- Display group 016: Activation of Heated rear window -Z1-, activation of Heated front window -Z2-, activation of auxiliary heating (not for USA) and cut-off conditions for auxiliary heating request (not for USA)
- Display group 017: Measuring values for Sunlight Photo Sensor -G107-, signal from windshield wiper switch for washer pump and windshield wiper
- Display group 018: Measured voltage at terminal "75", terminal "15", time period "ignition off" transmitted from instrument cluster and transmitted ignition key assignment
- Display group 019: Input signal from auxiliary heating, running light on/off (terminal "58") and version of communication-matrix in A/C Control Head -E87-
- Display groups currently not to be used by dealerships
- Air conditioning, electrical testing
- Wire and component test using VAG1598 A test box
- Electrical testing (vehicles up to model year 2001)
- Notes
- Electrical tests (to be performed on A/C Control Head -E87-) overview
- Test step 1 - Voltage supply, Ground (GND) connection and illumination for A/C control head -E87-
- Test step 2 - Temperature sensors
- Test step 3 - Fresh air blower -V2- and Control module for fresh air blower -J126-
- Test step 4 - Air conditioner positioning motors with potentiometers
- Test step 5 - A/C Pressure Switch -F129-, output for "A/C compressor cut-in" and signal indicating "engine temperature too high"
- Test step 6 - Voltage supply for A/C clutch -N25-, activation of Coolant fan -V7- and activation of A/C clutch -N25- Activation of A/C clutch -N25-)
- Test step 7 - Outputs and inputs for certain vehicle equipment with diesel engine/for solar sunroof (not for USA)
- Electrical testing (vehicles from model year 2002)
- Notes
- Electrical tests overview on A/C Control Head -E87-
- Test step 1 to 4
- Test step 5 to 9
- Test step 5: Pressure signal from High Pressure Sensor -G65-
- Notes
- Checking pressure signal from High Pressure Switch -G65-
- Connector assignment at High Pressure Switch -G65-
- Pressure signal from High Pressure Sensor -G65-
- For vehicles with compressor using A/C Compressor Regulator Valve -N280- (coding of A/C control head -E87-)
- For vehicles with A/C compressor regulator valve -N280- (coding of -E87-)
- For vehicles with compressors using A/C clutch -N25-(coding of -E87-):
- Test step 6: Activation for A/C Compressor Regulator Valve -N280-
- Test step 7: A/C Clutch Relay -J44- and activation of A/C clutch -N25-
- Test step 8: Activation of Coolant Fan -V7- (step 1 and 2)
- Test step 9: Sunlight Photo Sensor -G107-
- Test step 10: Input for engagement signal of A/C Control Head -E87- for vehicles with solar cells
- Test step 5: Pressure signal from High Pressure Sensor -G65-
- Rear window heating, electrical testing
- Solar sunroof, electrical testing
- Sensor for air quality -G238-, function
- Sensor for air quality -G238-, checking
- CAN-bus system, checking
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.