Function

Function

The A/C Control Head -E87- receives information from electrical and electronic system components (sensors), and then processes this information according to specified values.

The output signals from the control unit then activate the relevant electrical components (actuators).

To determine the cause of a malfunction or open circuit quickly, the A/C Control Head -E87- is equipped with a Diagnostic Trouble Code (DTC) memory which can be checked using the VAG 1551 Scan Tool (ST), VAS 5051 Vehicle Diagnostic Testing and Information System or VAG 1552 mobile Scan Tool (ST).

If malfunctions occur in the monitored sensors or components, they are stored as DTCs in DTC memory together with an indication of the malfunction type.

On Board Diagnostic (OBD) must always be performed before commencing troubleshooting. Stored information must be checked using the VAG 1551 Scan Tool (ST), VAS 5051 Vehicle Diagnostic Testing and Information System or VAG 1552 mobile scan tool.

The displayed malfunction information can be checked against the DTC table, which indicates possible malfunction causes and enables appropriate repair measures to be taken.

Notes on repairing malfunctions:
- Data output is only possible if the ignition is switched on or if the engine is running at a speed of less than 3000 RPM. At higher engine speeds, data output is restricted or aborted. For example, the output Diagnostic Test Mode (DTM) is only possible at engine speeds of up to 3000 RPM, and the On Board Diagnostic (OBD) program is aborted if this speed is exceeded).
- If a malfunction exists for more than a predetermined period, the DTC is stored as a static malfunction. If the malfunction is no longer detected for another predetermined period of time, it is re-classified as a sporadic malfunction. This process is continuously repeated. Sporadic malfunctions are identified by "/SP," which appears at the right of the display.
- If a sporadic malfunction does not occur for a predetermined period, it is automatically erased.

On Board Diagnostic (OBD) is only possible using VAG 1551 Scan Tool (ST), VAS 5051 Vehicle Diagnostic Testing and Information System or VAG 1552 mobile Scan Tool (ST) ("Rapid data transfer" operating mode 1).

On Board Diagnostic (OBD) is not restricted to storing and checking Diagnostic Trouble Codes (DTC), erasing and Output Diagnostic Test Mode (Output DTM). It also has basic setting, control unit identification and coding functions.

Blink code output" operating mode 2 is not available for the heating and air conditioning electronics.

"Self test" operating mode 3 and "Dealership code" operating mode 4 only concern the VAG 1551 and VAG 1552 scan tools and are described in the relevant operating instructions.

Available On Board Diagnostic (OBD) functions.

NOTE:
- This Repair instructions describes On Board Diagnostic (OBD) using the VAG 1551 Scan Tool (ST).
- OBD can be performed in the same way using the VAG 1552 mobile Scan Tool (ST). Before DTC memory is checked and erased, it is advisable to connect the VAG 1551 or VAS 5051 and print out the existing DTCs so that a record of any malfunction is available at a later stage. (The VAG1552 does not have a printer.)