With Manufacturer's Scan Tool
A/C System Signals, Checking
Special tools and equipment
- Scan Tool (ST) VAG 1551/1552 with cable VAG 1551/3
- VAG 1598/22 test box
- Digital multimeter US 1119 (Fluke 83 or equivalent)
- VAG 1594 adapter kit
- Wiring diagram
Test conditions
- A/C function OK.
- No DTCs stored in DTC memory.
- All electrical consumers, e.g. lights and rear window heating switched off.
- Battery 11.5 volts minimum.
- Vehicle at room temperature.
- A/C switched on.
Compressor shut-off, checking
The A/C control head signals the Engine Control Module (ECM) -J248- that the A/C compressor will be switch on, via the A/C compressor signal.
Using the same wiring, the A/C compressor is switched off by the ECM under the following circumstances:
NOTE:
- Hard acceleration from low speed
- In emergency program (limp mode)
- Engine Coolant Temperatures exceeds + 120 °C (248 °F)
- After every engine start for approx. 6 seconds.
Checking
- Connect VAG 1551/1552 Scan Tool.
- Start engine and let idle.
- Press -0- and -1- buttons to select address word 01: Engine electronics".
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -3- for "Output Diagnostic Test Mode" and confirm with -Q- button.
Indicated on display:
Rapid data transfer Q
03 Output Diagnostic Test Mode
- Confirm input with -Q- button.
Indicated on display:
Output Diagnostic Test Mode ->
Commencement of injection valve -N108
- Press -> button.
Indicated on display:
Output Diagnostic Test Mode ->
Exhaust gas recirculation valve -N18
- Press -> button.
Indicated on display:
Output Diagnostic Test Mode ->
A/C compressor interrupt
- A/C compressor shut-off is checked.
- A/C compressor must stop within 5 secs., (visual check) then start approx. every 5 secs. and then stop.
If A/C compressor does not switch off:
- Proceed with function 3: Output DTM, until complete.
- Press buttons -0- and -6- to select function 06: "End output:.
- Press -Q- button to enter input.
- Switch off ignition.
- Remove wiper arms and cowl panel
See Wiper and Washer Systems.
- Connect test box VAG 1598/22 to Engine Control Module (ECM) -J248- wiring harness.
- Check wiring between test box sockets 16 and the A/C system for open circuit according to wiring diagram.
Wire resistance: Max. 1.5 ohms
See Electrical Wiring Diagrams.
- Check DTC memory, if necessary, repair malfunctions.
- Erase DTC memory. Clearing Diagnostic Trouble Codes
- Display readiness code. If DTC memory has been erased or Engine Control Module (ECM) -J248- was disconnected, readiness code must be reset. Scan Tool Testing and Procedures
A/C signal and engine speed adaptation, checking
This signal provides information to the ECM to maintain a smooth idle even while difficult demands are place upon the engine by the A/C system.
Test sequence
- Connect VAG 1551/1552 Scan Tool.
- Start engine and let idle.
- Press -0- and -1 - buttons to select address word 01: "Engine electronics".
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- for "Read measured value block" and confirm with -Q- button.
Indicated on display:
Read measured value block HELP
Input display group number XXX
- Press buttons -0-, -0- and -2- for "Display group number 2" and confirm with -Q- button.
Indicated on display: (1. .4 = Display fields)
Read measured value block 2 ->
1 2 3 4
- Switch on air conditioner by pressing A/C button.
- Set lowest temperature and highest blower speed. A/C compressor must run.
Read measured value block 2 ->
960 rpm 0.0% 111 30.0 °C
- Observe display in display field 3, (3rd position from left)
- Specified Value: x x 1 (A/C system signal)
- Press -> button.
- Press buttons -0 and -5- for "End output" and confirm with -Q- button.
- Switch off ignition.
If specification not obtained:
- Remove wiper arms and cowl panel.
- Connect test box VAG 1598/22 to ECM wiring harness.
- Check wiring between test box socket 48 and A/C system for open circuit using wiring diagram.
- Wire resistance: Max. 1.5 ohms
See Electrical Wiring Diagrams.
If no malfunction can be found in wiring:
- Check function of A/C Engine Control Module (ECM) -J248- signal.
- Check DTC memory, if necessary, repair any malfunctions and erase DTC memory.
- Display readiness code. If DTC memory has been erased or Engine Control Module (ECM) -J248- was disconnected, readiness code must be reset. Testing and Inspection