With Manufacturer's Scan Tool

A/C Compressor Signal, Checking

Special tools, workshop equipment, testers, measuring instruments and auxiliary items required







- VAG 1551 Scan tool (or VAG 1552) with VAG 1551/3 adapter cable

NOTE: All functions which could previously be performed with VAG 1551/1552 can also be performed with the VAS 5051.

- VAG 1526 Hand multimeter or VAG 1715 multimeter
- VAG 1594 Adapter set
- VAG 1598/31 test box
- Electrical Wiring Diagrams

Test prerequisites







- The fuses must be OK.
- The battery voltage must be at least 11.5 V.
- All electrical accessories, e.g. lights and rear window heating must be switched off.
- Selector lever must be in position "P" or "N" on vehicles with an automatic transmission.
- Air conditioner functioning OK.
- Air conditioner must be turned off.
- Vehicle at room temperature (warmer than + 15 degrees C).
- No Diagnostic Trouble Code (DTC)s must be stored in DTC memory.
Reading Diagnostic Trouble Codes

Test sequence
- Connect VAG 1551 Scan tool (or VAG 1552) and select engine electronics control module with the "Address word" 01. When doing this the engine must be running at idle speed: ((VAG 1551 and Motronic Engine Control Module (ECM) -J220-, connecting and selecting).
[1][2][3]Connecting VAG 1551 Scan Tool

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- for function "Read measured value (data) block" and confirm entry with -Q- button.

Indicated on display:


Read measured value block
Input display group number XXX


- Press buttons -0-, -5- and -0- for "Display group number 50" and confirm entry with -Q- button.

Indicated on display: (1 to 4 = display zones)


Read measured value block 50
1 2 3 4


- Check displays in display zones 3 and 4:
Indicated in display zone 3:
A/C-Low
Indicated in display zone 4:
Compr. OFF
- Switch on air conditioning system.
- Select lowest temperature and highest blower speed.

The display in display zone 3 must change to:
A/C-High.

The display in display zone 4 must change to:
Compr. ON.

- Press the -> button.
- Press buttons -0- and -6- for function "End output" and confirm entry with the -Q- button.
- Switch off ignition.

If the displays do not change as described:
- Remove wiper arms and cowl panel:







- Connect VAG 1598/31 test box to control module wiring harness. The Motronic Engine Control Module (ECM) -J220- remains disconnected.
- Check wiring for open circuit between test box sockets 40 and 41 and air conditioning system referring to Electrical Wiring Diagrams. Wire resistance: max. 1.5 ohms

If no malfunctions can be found in the wiring:
- Check function of air conditioning system.
- Check DTC memory, repair malfunctions if necessary and then erase DTC memory.
Reading Diagnostic Trouble Codes

- Read readiness code. If the DTC memory has been erased or the Motronic Engine Control Module (ECM) -J220- was disconnected from battery positive (B+), the readiness code must be generated again.
Monitors, Trips, Drive Cycles and Readiness Codes
Monitors, Trips, Drive Cycles and Readiness Codes