Test Point 6 - Hot wire mass air flow sensor

TEST POINT 6 - Hot wire mass air flow sensor (V/Ohms) - Fault code 1_21

Possible Causes, Elimination, Remarks
Voltage supply (V)

Turn plug at hot wire mass air flow sensor anti-clockwise and disconnect. Connect voltmeter to terminals 1 and 3.




Bridge Digital Motor Electronics (DME) relay
Pull DME relay (R 53) off the central electrical system and bridge plug-in contacts 30 and 87 b (identifications 3 and 7 on central electrical system) with fuse-protected shop-made cable. The fuel pump should now start operating.

Ignition on:
Display: Voltage approx. 10.8 Volts.

No display: check in accordance with wiring diagram Reconnect plug.

Checking the hot wire signal with System Tester 9288

The mass air flow sensor signal may be tested directly in the Actual values menu item using System Tester 9288.

To check the signal, remove upper air cleaner section and start engine.

Display: approx. 1.0 Volt

Blow against hot wire.
This must cause the System Tester display to change.




Checking the hot wire signal (V)
- Connect plug to mass air flow sensor.
- Pull off DME plug.
- Bridge DME relay.
- Connect DME plug terminal 36 to ground (e.g. door stop). Connect voltmeter to DME plug terminal 7 and 26 (ground).

Display: 160 mV

Blow against hot wire in mass air flow sensor and observe voltmeter. A voltage change must occur.