Air Mass Sensor

TEST PROCEDURE:

Status Monitoring:
The Load Signal (tL) provides an indication of the measured air flow rate in the Air Mass Meter (MAF). When idling, the value should be 2.0 ms ± 20%. In the case of a break in the voltage supply or in the signal line, the value is a constant 2.20 ms (substitute value) at idle speed and 0 ms under part load and full load.

The load signal is formed dependent upon the voltage (<5 V) applied at the hot wire of the MAF. The load signal is displayed only when the engine is in operation.

The voltage value of the hot wire can be measured between Pin 14 (sensor ground) and Pin 41 (signal MAF) of the Digital Motor Electronic (DME) control unit. The measurement can also be conducted with the ignition "ON" (nominal value approx. 1.4 V).

The load signals of the two rows of cylinders should deviate only slightly from each other. Check the burn-clear function if the load signal is permanently too low. A load signal which is too low tends to produce a lean mixture, thus reducing the engine output.

Voltage Supply Check:
Voltage supplied between Pins 2 and 4 at the MAF.

Check Burn-Clear Function:
Increase engine speed once to above 2000 rpm (engine temperature >140°F) (>60 C). Approx. 5 seconds after switching "Off" the engine, the hot wire can be seen to briefly light up (burn-clear) at the MAF (air cleaner cover removed).

Within 5 sec after switching "Off" the engine, a voltage of approx. 3.5 V is applied at Pin 13 for 0.5 sec. to bum clear the hot wire. This signal can be measured between Pin 13 and vehicle ground.