A/C System, On Board Diagnostic (OBD)

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 in accordance with specified values and then provides corresponding output signals that control electrical components (actuators).

The control head is controlled by an internal microprocessor with On Board Diagnostic (OBD) capability. If faults or open circuits occur on applicable components, Diagnostic Trouble Codes (DTC) are stored in DTC memory. Stored faults are identified using either VAG1551 Scan Tool (ST) or VAG1552 Scan Tool (ST). Tables containing all DTCs and corresponding repair information guide technicians through the OBD process.

NOTE:
- This Repair Information describes On Board Diagnostic (OBD) with VAG1551 Scan Tool (ST). OBD procedures can also be performed with VAG1552 Scan Tool (ST) (VAG1552 Scan Tool is not equipped with a printer).
- Scan Tool VAG1551 or 1552 must be used in in operating mode -1- (Rapid data transfer).
- Operating mode -2- (Flash code output) is not provided for A/C and Heating OBD.
- Always check DTC memory and perform necessary repairs before erasing DTC memory.
- DTC output is possible only if ignition is on or engine is running and engine speed is less than 3000 rpm (if engine speed is higher, output is possible only for a limited time or is terminated).
- If a fault exists for a certain time it is stored as a static fault.
- If a static fault is no longer present after a certain time, it is stored as a sporadic fault and the reference "SP" appears on the upper right of the VAG1551 display/print-out.
- Before replacing a suspected malfunctioning component, check all related wiring, connections, harness connectors and Ground (GND) connections according to the appropriate wiring diagram.
- Output Diagnostic Test Mode (DTM), Basic Setting, A/C control head identification and coding functions are also possible.
- A/C system component locations: engine compartment
- A/C system component locations: passenger compartment
- If a the display of a newly installed A/C control head -E87- flashes after switching the ignition on (for approximately 2 minutes), code the control head and execute basic setting. [1][2]Basic Setting (Function 04)
- If a replacement control head is not coded after installation or if an unrecognized code was entered, code "00042" (4-cyl. gasoline engine USA) is stored.
- Control of A/C compressor, flap motors and fan motors etc. is not possible when executing Output Diagnostic Test Mode (DTM), function 03 and basic setting, function 04. A/C control is possible in all other functions.