A/C System Signals, Checking
Special tools, workshop equipment, testers, measuring instruments and auxiliary items required
- VAG 1551/1552 Scan Tool using VAG 1551/3 adaptor cable
- VAG 1598/22 Test Box
- VW 1594 Adaptor kit
- VAG 15278 Voltage tester
- Wiring diagram
Checking requirements
- A/C function OK.
- No DTCs stored in DTC memory. Checking DTC Memory (Function 02)
- Vehicle at room temperature (warmer than + 15 °C).
- A/C system switched ON
A/C compressor shut-off, checking
NOTE: Using other system connections, the ECM has the ability to switch off the A/C compressor under the following operating conditions:
- Under hard acceleration at low speeds
- When in emergency program (limp home operation)
- When Engine Coolant Temperatures exceed + 120 °C
- For approx. 6 seconds after each start sequence
Test sequence
- Connect VAG 1551/1552 Scan Tool. [1][2]Reading and Clearing Diagnostic Trouble Codes
- Start engine and let idle
- Press 0 and 1 buttons to select Address word 01: "Engine electronics"
Display will appear as shown
Rapid data transfer HELP
Select function XX
- Press 0 and 3 buttons to select Function 03: "Output Diagnostic Test Mode"
- Press Q button to enter input
Display will appear as shown
Rapid data transfer Q
03 Output Diagnostic Test Mode
- Press Q button to enter input
Display will appear as shown
Output Diagnostic Test Mode ->
Cold start injector N108
- Press -> button.
Display will appear as shown
Output Diagnostic Test Mode ->
EGR Vacuum Regulator solenoid valve N18
- Press -> button.
Display will appear as shown
- A/C compressor shut-off is checked.
- The A/C compressor must stop within 5 seconds (visual check) then start approx. every 5 seconds and then stop.
Output Diagnostic Test Mode ->
A/C Compressor interruption
If A/C compressor not switched OFF
- Proceed with Output Diagnostic Test Mode until completed.
- Press 0 and 6 buttons to select Function 06: "End output"
- Press Q button to enter input
- Connect VAG 1598/22 Test Box to ECM harness connector.
- Check wiring for open circuit between Test Box sockets 16 and A/C using Wiring diagram.
- Wire resistance: Max. 1.5 Ohms
See Wiring diagrams, Electrical Troubleshooting and Component locations.
- Display Readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased
- Create Readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
A/C signal and smooth idle control system, checking
NOTE: This signal provides information to the Engine Control Module so it can maintain a smooth idle speed even while difficult demands are placed upon the engine by the A/C system.
Test sequence
- Connect VAG 1551/1552 Scan Tool. [1][2]Reading and Clearing Diagnostic Trouble Codes
- Start engine and let idle
- Press 0 and 1 buttons to select Address word 01: "Engine electronics"
Display will appear as shown
Rapid data transfer HELP
Select function XX
- Press 0 and 8 buttons to select Function 08: "Read measuring value block"
- Press Q button to enter input
Display will appear as shown
Read measuring valve block HELP
Input display group number XXX
- Press 0, 0 and 2 buttons to select "Display group 2"
- Press Q button to enter input
Display will appear as shown (1 to 4 = Display zones)
Read measuring value block 2 ->
1 2 3 4
- Observe display in display zone 2.
Specified value X X 0 (A/C signal)
Read measuring value block 2 ->
1 2 010 4
- Switch ON A/C by pressing "Auto" button and selecting lowest temperature
- A/C compressor must run
- Observe display in display zone 2.
Specified value X X 1 (A/C signal)
Read measuring value block 2 ->
1 2 111 4
If specification not obtained
- Connect VAG 1598/22 Test Box to ECM harness connector.
- Check wiring for open circuit between Test Box sockets 8 and A/C using Wiring diagram.
- Wire resistance: Max. 1.5 Ohms
- Display Readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased
- Create Readiness code. Monitors, Trips, Drive Cycles and Readiness Codes