With Manufacturer's Scan Tool

Charge Air Pressure System, Checking

Special tools and equipment



^ VAG 1390 Hand vacuum pump or equivalent
^ Fluke 33 Multimeter or equivalent
^ VAG 1594 A Test kit
^ VAG 1598/22 Test box
^ VAG 1551/1552 Scan Tool with adapter cable VAG 1551/3
^ Wiring diagram

Requirements



^ Fuse No. 34 OK
^ Battery voltage must be at least 11.5 V
^ No leaks in intake and exhaust system.
^ No malfunctions in the engine or fuel injection system such as start of injection, injectors, compression pressures.
^ The engine coolant temperature must be at least 85°C (185°F)

Test sequence
Observe caution notes
- Connect VAG 1551/1552 Scan Tool and select engine control module, address word 01. The engine must run at idle.

Note: Instead of VAG 1551 Scan Tool also VAG 1552 Scan Tool can be used, however, no print-out can be made.





Display will appear as shown
- Press -0- and -8- buttons to select "Read measuring value block" function 08.
- Press -Q- button to enter input





Display will appear as shown
- Press -0-, -1- and -1- buttons to select Display Group 11
- Press -Q- button to enter input.
Read measuring value block 11





Display will appear as shown
- Accelerate vehicle in 3rd gear from about 1500 rpm to wide open throttle.
- Press VAG 1551 PRINT button at approx. 3000 rpm.
Read measuring value block 11





Specification: 1700 to 2200 mbar (in display field 3)
If specification was obtained:
- Press button.
- Press buttons -0- and -6- to select "End output" function 06.
- Press -Q- button to enter input
If specification was not obtained:
- Perform Output Diagnostic Test Mode (function 03) to activate the Wastegate Bypass Regulator Valve -N75-.





Display will appear as shown
The valve must function and the boost pressure control rod must move back and forth (at least 3 to 4 times), as long as there is a vacuum in the vacuum reservoir.
- Press button.
- Press buttons -0- and -6- to select "End output" function 06.
- Switch ignition off.
If the boost pressure control rod does not move and the specifications are not obtained, replace the turbocharger.
If the rod does not move because Wastegate Bypass Regulator valve -N75- is not working:
- Check Wastegate Bypass Regulator valve -N75-.
- Check vacuum hoses.
If rod does not move but bypass regulator valve works:





- Connect VAG 1390 or equivalent vacuum pump to wastegate bypass regulator valve and check rod for ease of movement.
If rod does not move easily:
- Replace turbocharger assembly.

Wastegate Bypass Regulator valve -N75-, checking





Disconnect 2-pin electrical connector from wastegate bypass regulator valve (arrow).

Resistance, checking





- Measure resistance between terminals of bypass regulator valve.

Engine code ALH
^ Specification: 14.0 to 20.0 Ohms

Note: At room temperature the resistance value is at the lower tolerance range, at operating temperature the resistance is in the upper tolerance range.

If specification not obtained:
- Replace Wastegate Bypass Regulator valve -N75-.
- Check Diagnostic Trouble Code (DTC) memory.
- Read readiness code.
If DTC memory was erased or engine control module is subject to low voltage with ignition ON, reset readiness code.
If the specification was obtained:
- Check voltage supply of Wastegate Bypass Regulator valve-N75-.

Voltage supply, checking





- Connect multimeter and check voltage supply.
- Connect jumper wire from test kit VAG 1594 to terminal 1 and engine ground
- Switch ignition on.
^ Specification: 11.5V
If specification was not obtained:
- Switch ignition off.
- Remove windshield wiper arms and plenum cover.





Connect test box VAG 1598/22 to harness connector of engine control module.





- Check wiring between test box and contact terminals for open circuits according to wiring diagram:
^ Wiring resistance: max. 1.5 Q
- Check wires for short circuit one against another, to vehicle ground and to battery B+.
^ Wiring resistance: cc
If no malfunctions and if voltage between terminal 1 + ground:
- Replace Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM).
- Check DTC memory.
- Read readiness code.
If the DTC memory was erased or the engine control module is subject to low voltage with ignition ON, reset the readiness code.