With Generic Scan Tool

Modulating Piston Displacement Sensor And Quantity Adjuster, Checking

The quantity adjuster is an electro-magnetic swivelling positioner which is controlled by the ECM via a directed duty cycle. 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 position of Quantity Adjuster -N146- therefore determining the amount injected.


NOTE: Use only gold-plated terminals when servicing terminals in harness connector to injection pump quantity adjuster.


Recommended special tools and equipment
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirement







- The respective fuses of Diesel-Direct fuel injection system must be OK.
- Battery voltage must be at least 11.5 Volts.

Test sequence

Modulating Piston Displacement Sensor -G149-, checking







- Disconnect 10-pin harness connector for quantity adjuster (harness connector to injection pump quantity adjuster) -arrow-.







- Measure resistance between connector terminals 1 + 2 and 2 + 3.
Specified value: 4.9...7.5 Ohm

If specified value is not obtained:
- Replace injection pump, item 3. Procedures
- Erase DTC memory of control module for Diesel-Direct fuel injection system, Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If specified value is obtained:
- Connect test box to control module wiring harness, connect test box for wiring test. Test Box, Connecting For Wiring Test

Vehicles with 80-pin control module







- Check for open circuit in wires between test box and connector according to wiring diagram.
Terminal 1 + socket 56
Terminal 2 + socket 57
Terminal 3 + socket 64
Wire resistance: max. 1.5 Ohm

Vehicles with 121-pin control module







- Check for open circuit in wires between test box and connector according to wiring diagram.
Terminal 1 + socket 108
Terminal 2 + socket 106
Terminal 3 + socket 99
Wire resistance: max. 1.5 Ohm

Continuation for all vehicles
- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+.
Specified value: Infinite Ohm

If no malfunctions are detected in wires:
- Replace Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248-
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

Checking Quantity Adjuster -N146-







- Disconnect 10-pin harness connector for quantity adjuster (harness connector to injection pump quantity adjuster) -arrow-.







- Measure resistance between connector terminals 5 + 6.
Specified value: 0.5...2.5 Ohm

If specified value is not obtained:
- Replace injection pump, item 3 .
- Erase DTC memory of control module for Diesel-Direct fuel injection system, Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If specified value is obtained:
- Connect test box to control module wiring harness, connect test box for wiring test. Test Box, Connecting For Wiring Test

Vehicles with 80-pin control module







- Check for open circuit in wires between test box and connector according to wiring diagram.
Terminal 5 + socket 2
Terminal 5 + socket 28
Terminal 6 + socket 59
Terminal 6 + socket 66
Terminal 6 + socket 80
Wire resistance: max. 1.5 Ohm

Vehicles with 121-pin control module







- Check for open circuit in wires between test box and connector according to wiring diagram.
Terminal 5 + socket 1 and 2
Terminal 6 + socket 121 and 116
Wire resistance: max. 1.5 Ohm

Continuation for all vehicles
- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+.
Specified value: Infinite Ohm

If no malfunctions are detected in wires:
- Replace Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248-
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes