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

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.