Air Flow Meter/Sensor: Testing and Inspection
Mass Air Flow (MAF) Sensor, Checking
The Mass Air Flow (MAF) sensor signal is used by the control module to calculate the permissible injection quantity and to regulate Exhaust Gas Recirculation (EGR). The smaller the MAF sensor signal is, the smaller fuel may be injected.
NOTE: Use only gold-plated terminals when servicing terminals in harness connector of Mass Air Flow (MAF) sensor.
Recommended special tools and equipment
- V.A.G1526 multimeter or V.A.G1715 multimeter
- V.A.G1594 connector test kit
- Wiring diagram
Test requirement
- The respective fuses of Mass Air Flow (MAF) Sensor -G70- must be OK:
- Battery voltage must be at least 11.5 volts.
- All electrical consumers such as, lights and rear window defroster must be switched off.
- For vehicles with automatic transmission, selector lever must be in position -P- or -N-.
- If vehicle is equipped with an A/C system, it must be switched off.
- Ground (GND) connections between engine and chassis must be OK.
- Coolant temperature must be at least 80 degrees C, Diagnostic mode 1: Check measured values; PID 5, Coolant temperature. Diagnostic Mode 1: Check Measured Values
Function test
- Connect diagnostic tester. Diagnostic Tester, Connecting
- Start engine and let run at idle. Under address word 33, select "Diagnostic mode 1: Checking measured values."
- Select the measuring value "PID 16: Air flow quantity at Mass Air Flow (MAF) sensor".
- Check specified value of air flow quantity at Mass Air Flow (MAF) Sensor at idle:
Vehicles with engine code ALH:
Specified value: 2.80 to 5.30 g/sec
Vehicles with engine code BEW:
Specified value: 1.80 to 4.30 g/sec
- End diagnosis and switch ignition off.
If specified value is obtained, but DTC memory has a DTC concerning Mass Air Flow (MAF) sensor:
- Check voltage supply of Mass Air Flow (MAF) sensor.
If specified value is not obtained:
- Check signal and Ground (GND) wires of Mass Air Flow (MAF) sensor.
Voltage supply for Mass Air Flow (MAF) sensor, checking
- Disconnect 5-pin connector from Mass Air Flow (MAF) Sensor (arrow).
- Switch ignition on.
- Measure voltage supply for MAF sensor between the following connector terminals:
If specified values are obtained:
- Replace Mass Air Flow (MAF) Sensor -G70-
- 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 values are not obtained:
- Check signal and Ground (GND) wire of Mass Air Flow (MAF) sensor.
Checking signal and Ground wires of Mass Air Flow (MAF) Sensor
- 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 circuits in wires between test box and harness connector according to wiring diagram.
Terminal 2 + socket 2
Terminal 2 + socket 28
Terminal 3 + socket 4
Terminal 4 + socket 50
Terminal 5 + socket 52
Wire resistance: max. 1.5 Ohms
Vehicles with 121-pin control module
- Check for open circuits in wires between test box and harness connector according to wiring diagram.
Terminal 2 + socket 1 and 2
Terminal 3 + socket 49
Terminal 4 + socket 30
Terminal 5 + socket 68
Wire resistance: max. 1.5 Ohms
Vehicles with 154-pin control module
- Connect adapter cable (V.A.G 1598/39-2) to test box (V.A.G 1598/42).
- Check for open circuits in wires between test box and harness connector according to wiring diagram.
Terminal 2 + socket 18
Terminal 3 + socket 60
Terminal 4 + socket 40
Terminal 5 + socket 82
Wire resistance: max. 1.5 Ohms
Continue for all vehicles
- Check wires for short circuit to each other, to vehicle Ground (GND) and to B+.
Specified value: Infinite Ohms
If no malfunctions are found in wires:
- Replace Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248-.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes