Description of On-Board Diagnostics
A/C system, On Board Diagnostic (OBD)
Function
The A/C control head -E87- receives input information from various electrical and electronic components (sensors).
This information is processed by the control head according to specified values and then provides corresponding output signals that control electrical components (actuators).
The A/C control head -E87- is controlled by an internal microprocessor with On Board Diagnostic (OBD) capability. If malfunctions or open circuits occur on applicable components, Diagnostic Trouble Codes (DTC) are stored in memory.
When starting On Board Diagnostic program, always check the stored information with VAG1551 Scan Tool (ST) or VAG1552 Scan Tool (ST).
Malfunctions recognized by OBD are assigned DTCs and an indication of the malfunction type. Tables containing all DTCs and corresponding repair information guide technicians through the OBD program.
On Board Diagnostic (OBD)
Beginning with model year 1998, a sensor for air quality -G238- will also be offered for the Audi A8. Vehicles with -G238- are identified by button -A- for "Automatic recirculating air," instead of the "OFF" button on A/C control head -E87-.
For vehicles equipped with sensor for air quality -G238- only the new A/C control head -E87-, beginning with Part No. index letter "J" should be installed (only from this index is the software for the operation in a vehicle with the air quality sensor applicable).
4D0820 043J D2-A/C fully automatic DXX
Code XXXXX WSC ZZZZZ
NOTE:
- DTC output is possible only if ignition is switched on or engine is running and engine speed is less than 3000 RPM. If engine speed is higher, output is possible only to a limited extent or is terminated.
- If a DTC exists for a certain time it is stored as a static DTC. If a static DTC is no longer present after a certain time, it is stored as a sporadic DTC and the letters "SP" appears on the upper right of VAG1551 display/printout. If a sporadic DTC no longer occurs for a certain time, it is automatically erased.
- Before replacing a suspected malfunctioning component, check all related wiring, connections, harness connectors and Ground (GND) connections according to the appropriate wiring diagram.
In order to have documentary evidence of a Diagnostic Trouble Code (DTC) which may exist for subsequent inquiries, it is a good practice to connect VAG1551 Scan Tool and print out the DTCs which exist before erasing the DTC memory (VAG1552 is not equipped with a printer).
VAG1551 or 1552 Scan Tools must be used in in operating mode -1- (Rapid data transfer). Operating mode -2- (Blink code output) is not provided for in A/C and heating system OBD. Operating mode -3- (self test) and -4- (dealership code) relate only to the VAG1551 or VAG1552 Scan Tool and are described in Scan Tool operating instructions.
Always check DTC memory and perform necessary repairs before erasing DTC memory. Output Diagnostic Test Mode (DTM), basic setting, A/C control head identification and coding functions are also possible in OBD program.
Technical data
System changes, Up To M.Y. 2000
There is a new A/C control head -E87- (Part No. 4D0 820 043 J).
CAUTION!
Part numbers are listed here for reference only. Always check with your Parts department for the latest information.
NOTE:
- A sensor for air quality -G238- will be introduced during model year 1998.
- For vehicles equipped with sensor for air quality -G238- only the new A/C control head -E87-, beginning with Part No. index letter "J", should be installed (only from this index is the software for the operation in a vehicle with the air quality sensor applicable)
- Vehicles equipped with sensor for air quality -G238- can be identified by button -A- for automatic air recirculation instead of the "OFF" button, on the A/C control head.
- While in "Automatic air recirculation" mode the compressor (depending on the pollutant content of the recirculating air) can be switched on down to an outside temperature of approx. -8 °C (-18 °F), in contrast to +2 °C (36 °F) while in other operating modes.
- The coding for A/C control head -E87- has been revised.
The following components which are monitored by A/C control head -E87- are deleted:
- A/C low pressure refrigerant switch -F73-
- A/C refrigerant high pressure switch -F118-
The following components which are monitored by A/C control head -E87- are new:
- A/C pressure switch -F129-
- Sensor for air quality -G238-
The following signals which are monitored or processed by A/C control head -E87- are new:
- Input signal "Requirement for automatic recirculated air" from sensor for air quality -G238-
- Signal for triggering wiper/washer intermittent relay -J31-