EMS Sensors (page 7 of 13)

ENGINE MANAGEMENT SYSTEM - SIEMENS

18-4-20 DESCRIPTION AND OPERATION

MAF Sensor

The MAF sensor provides a signal which the ECM uses for engine load calculations.

The MAF sensor is a hot film type, and is located in the intake system between the air filter housing and the throttle 
body.

A closed-loop control circuit in the MAF sensor maintains a thick film resistor at a constant 200

°

C (392

°

F) above 

ambient temperature. The current required to maintain the temperature of the thick film resistor, against the cooling 
effect of the air flowing through the sensor, provides a precise, non-linear, measure of the air mass entering the 
engine.

The MAF sensor receives a battery voltage power supply and generates an output signal to the ECM, between 0 and 
5 volts, which is proportional to the air mass drawn into the engine.

In the event of a MAF sensor signal failure, the following symptoms may be apparent:

l

During driving engine speed may dip before recovering.

l

Difficult starting.

l

Engine stalls after starting.

l

Delayed throttle response.

l

Reduced engine performance.