The purpose of the Mass Air Flow sensor is to measure the air flow into the engine.
|Part Number||034 133 471 K||Bosch 0208 213 007|
The picture below displays the MAF and its position in the engine bay next to the airbox.
1. To test the MAF, unplug the connector in the picture above
2. Connect a diode test LED between contact 1 of the wiring connector and +12v (battery). The LED must light up.
If test LED fails to light up, an open circuit exists in the wiring to the connector.
3. Connect a diode test LED between contact 5 of the wiring connector and engine earth.Switch on ignition. The LED must light up.
If test LED fails to light up, an open circuit exists in the wiring to the connector or the ECU is faulty.
Check wiring from pin 37 of ECU harness to contact 5 of MAF connector. If open circuit is not found, replace the ECU.
4. Connect a diode test LED between contact 5 of the connector and engine earth. Switch on ignition and operate the starter for a few seconds.
The LED must light up when ignition is on and during starting.
If the LED goes out during starting, check fuse #28.
Check wiring from contact 5 of MAF connector to fuse #28 for open circuit.
Check wiring from fuse #28 to fuel pump relay (position 10) contact 59 for open circuit.
5. Check the following for open circuit wiring:
wiring connector contact 2 -> ECU harness contact 26
wiring connector contact 3 -> ECU harness contact 7
wiring connector contact 4 -> ECU harness contact 25
6. Measure resistance across contact 1 and contact 2 of the MAF connector.
Remove test cables and short together
Repeat resistance measurement. Second reading must be the same as the first reading.
If readings are >0.1ohm apart, the MAF should be replaced
7. Reconnect the connector to the MAF.
Pull back shroud and place test probes between contact 1 and contact 3 to measure DC voltage
Switch on igntion. Voltage should be between 1.5V and 2.5V.
Start engine and leave at idle. Voltage should be ~2.5V.
Blip throttle. Voltage should rise to ~3->5V
If voltages do not meet these values, the MAF should be replaced
Testing cleaning operation
The MAF has a self cleaning operation which is performed about 4 seconds after switching off the engine and takes about 1 second.
It only operates if the following conditions have been met
Coolant temperature > 60 degrees celsius
Engine speed > 2000rpm
All signal wires in order
Fuse #28 in order
It can be tested as follows:
Unscrew air mass meter from air cleaner housing and pull forwards sufficiently to allow observation of the operation.
Leave the connector in place.
Run engine and increase engine speed to over 2000rpm
Switch off engine and observe cleaning operation. The hot wire should glow brightly for ~1 second
If no cleaning operation is observed
Pull back shroud of connector and attach diode test LED between contact 1 and contact 4.
Repeat test sequence. The diode test LED should light up during cleaning operation.
If the diode test LED lights up, the MAF should be replaced.
If the diode test LED fails to light up, recheck all wiring above from MAF connector to ECU harness.If all in order, replace the ECU.
The MAF can also be cleaned chemically.
Remove intake hose
Unscrew bolts securing MAF to airbox
Place the MAF in a bath of IPA (IsoPropyl Alcohol)solution and leave to soak overnight.
Dry thoroughly before refitting.