Modulating Piston Displacement Sensor and Quantity Adjuster
The Quantity Adjuster is an electro-magnetic, swivelling positioner, controlled by the ECM via duty cycle (on-off ratio). The eccentric shaft on the Quantity Adjuster moves the modulating piston (on the high pressure piston) thereby regulating the quantity of fuel injected.The Modulating Piston Displacement sensor informs the ECM of the Quantity Adjuster N146 position and then calculates the required amount of fuel to inject.
Special Tools, Testers And Auxiliary Items:
- VAG 1551/1552 Scan Tool with VAG 1551/3 adaptor cable
- VAG 1598/18 Test Box
- Fluke 83 multimeter (or equivalent)
- VW 1594 adaptor kit
- Wiring diagram
Testing Procedure:
- Connect VAG 1551/1552 Scan Tool
- 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 value block HELP
Input display group number XXX
- Press 0, 0 and 1 buttons to select "display group 1"
- Press Q button to enter input
Display will appear as shown:
Read measuring value block 1 ->
840 rpm 6.5mg/H 1.480V 87.3°C
- Observe Engine Coolant Temperature in display zone 4
Specification: at least 85°C
NOTE: Continue with check only when Engine Coolant Temperature specification is obtained.
- Observe value in display zone 3
(voltage from Modulating Piston Displacement sensor)
- Observe voltage supply value in display zone 3 for Modulating Piston Displacement sensor:
Display will appear as shown:
Read measuring value block 1 ->
840 rpm 6.5mg/H 1.480V 87.3°C
Specification: 1.250 to 1.750 Volts
If specification not obtained:
- Check Modulating Piston Displacement sensor as described below
- Check Quantity Adjuster as described below
Modulating Piston Displacement Sensor G149, Checking:
- Press -> button
- Press 0 and 6 buttons to select Function 06 End data transfer"
- Press Q button to enter input
- Switch OFF ignition
- Disconnect fuel temperature sensor harness connector (connection to fuel pump Quantity Adjuster)
- Measure resistance between connector terminals: 1 + 2 and 2 + 3
Specification: 5 to 7 Ohms
If specification not obtained:
- Replace injection pump
- Display the readiness code
If DTC memory was erased:
- Create readiness code again
If specification obtained:
- Connect VAG 1598/18 Test Box to ECM harness connector
- Check wiring for open circuit between Test Box and connector using wiring diagram:
terminal 1 + socket 29
terminal 2 + socket 7
terminal 3 + socket 52
Wire resistance: max. 1.5 Ohms.
- Additionally check wires for short to one another.
Specification: Infinite Ohms
If wiring OK:
- Replace Diesel direct injection system ECM J248
- Display the readiness code
If DTC memory was erased:
- Create readiness code again
Quantity Adjuster N146 Checking:
- Press -> button
- Press 0 and 6 buttons to select function 06 "End data transfer"
- Press Q button to enter input
- Switch OFF ignition
- Disconnect Quantity Adjuster harness connector (connector to injection pump Quantity Adjuster).
- Measure resistance between connector terminals 5 + 6
Specification: 0.5 to 2.5 Ohms
If specification not obtained:
- Replace injection pump
- Display the readiness code
If DTC memory was erased:
- Create readiness code again
If specification obtained:
- Connect VAG 1598/18 Test Box to ECM harness connector
- Check wiring for open circuit between Test Box and connector using wiring diagram:
terminal 5 + sockets 23, 45 and 68
terminal 6 + sockets 4, 5 and 49 Wire
resistance: max. 1.5 Ohms
- Also check wires for shorting to one another
Specification: Infinite Ohms
If wiring OK:
- Replace Diesel direct injection system ECM J248
- Display the readiness code
If DTC memory was erased:
- Create readiness code again