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 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 Manual 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.
Testing and Inspection
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.
A/C System, on Board Diagnostic (OBD)
Heating and A/C system changes 1997
On Board Diagnostic changes
- New A/C control head -E87- with specific coding for m.y. 1997, 4-cyl. and 6-cyl. engines.
NOTE:
- Before performing On Board Diagnostic of A/C system, ensure A/C control head -E87 is coded correctly (according to engine application).
- A/C control heads beginning with Part No. 8L0 820 043 should only be installed in m.y. 1997 vehicles.
- A/C control heads beginning with Pad No. 8D0 820 043 must only be installed in vehicles through m.y. 1996.
CAUTION!
- Part numbers are for reference only.
- Always check for the latest information.
NOTE:
- For m.y. 1997, changes that affect monitoring of the A/C system by A/C control head -E87- were made.
- Monitored components, locations.
- Additional technical data and notes. (See Function)
- If a replacement A/C control head is not coded after installation or if an unrecognized code was entered, code "04142" (Audi A4 - 4-cyl. - USA) is stored.
- The A/C control head is no longer connected to terminal 30 (vehicle electronics). The last input setting (into the A/C control head) is stored when the ignition is switched off and retained when the ignition is switched on.
- The duration of time when ignition is off is calculated by the A/C control head. When ignition is switched on, the previous "standing time" is calculated by monitoring a time signal from the instrument cluster. If more than 4 hours pass since ignition was switched oft; the actual measured values of the outside temperature sensor are used as instantaneous outside and engine temperature inputs for A/C system control. If "standing time" is shorter than 4 hours, the actual measured values of the outside temperature sensor are suppressed and system output temperature control is calculated by the A/C control head. The "standing time" period is monitored and used for this calculation. (Heat radiating from the engine and radiator leads affects the measured value of the temperature sensor).
The following components previously monitored by OBD and triggered by A/C control head -E87- are deleted:
- Refrigerant low pressure switch -F73-.
- Refrigerant high pressure switch -F118- (low and high pressure switch functions integrated into A/C pressure switch, -F29-).
- Fresh air/recirculating flap two-way valve -N63-.
The following new components are monitored by OBD and provide input signals to -E87-:
- A/C pressure switch -F129-.
- Sender for outlet temperature, center -G191-
- Sender for outlet temperature, floor outlet -G192-.
The following components monitored by OBD or triggered by -E87- are revised:
- The heater/air conditioner assembly with all servo motors.
- The fresh air blower and control module.
Following components that provide input signals to the A/C control head -E87- are revised:
- Instrument cluster
A/C system changes
- Revised heating/air conditioner assembly with flap motors.
- The air flow flap motor now activates the fresh air/recirculating air flap as well.
- The two way valve for the circulating/fresh air door, the vacuum unit and the vacuum reservoir are deleted.
A/C refrigerant circuit changes
- New service valve connection on low pressure side.
- Service valve connection for high pressure side installed in high pressure line in plenum panel (deleted at condenser).
- A/C pressure switch -F129- replaces pressure switches -F73- and -F118-.
- New version "Zexel" compressor and high pressure line (4-cyl. engines only).
A/C System, Changes 1998 On
On Board Diagnostic (OBD)
There is a new A/C control head -E87- beginning with index "D" (Part No. 8L0 820 043).
CAUTION!
Part numbers are listed here for reference only. Always check with your Parts department for the latest information.
NOTE: For m.y. 1998 the A/C control head -E87- harness connector has changed (connections for illumination, terminal 58, terminal 58s).
For m.y. 1997 vehicles, install only A/C control head -E87- with Part No. 8L0 820 043 up to and including Part No. index letter "C."
8L0 820 043B A4-A/C fully automatic DXX
Coding XXXXX WSC ZZZZZ
For vehicles beginning m.y. 1998, install only A/C control head -E87- with Part No. 8L0 820 043 from Part No. index letter "D."
8L0 820 043D A4-A/C fully automatic DXX
Coding XXXXX WSC ZZZZZ