Mass Air Flow Sensor (X105)
The sensing element of a Mass Air Flow Sensor
(X105) is a “hot wire anomometer” consisting of two
wires; one heated, one not. The air flows across the
wires, cooling the hot wire and thereby altering its
resistance. The ECM (Z132) measures this change
in resistance and so calculates the amount of air
flowing into the engine.
If the Mass Air Flow Sensor (X105) fails, the engine
will start and then die as the engine reaches 550 rpm
before the ECM (Z132) looks for the Mass Air Flow
Sensor (X105) signal.
Throttle Position Sensor (X171)
This sensor is a variable resistor. The signal informs
the ECM (Z132) of the actual position of the throttle
plate. Failure of the Throttle Position Sensor (X171)
will result in poor idle and lack of throttle response. If
the Throttle Position Sensor (X171) fails in the
“closed” mode, then the engine will only rev up to
1740 rpm when the ECM (Z132) will initiate “over run
fuel cut–off”.
Heated Oxygen Sensors (X139, X160, X289, X290)
The heated oxygen sensor consists of a titanium
metal sensor surrounded by a gas–permeable
ceramic coating. Oxygen in the exhaust gas diffuses
through the ceramic coating on the sensor and
reacts with the titanium wire, altering the resistance
of that wire. From this change in resistance, the
ECM (Z132) can calculate the percentage of oxygen
in the exhaust gas and adjust the injected fuel
quantity that as to achieve the correct air/fuel ratio.
This reduces the emissions of Carbon Monoxide
(CO), Hydrocarbons (HC) and oxides of Nitrogen
(NOX) to acceptable levels.
Presently, two heated oxygen sensors are used, one
in each exhaust down pipe just before the catalyst.
In the event of sensor failure, the system will default
to ”open loop”. Operation and fuelling will be
calculated using signals from the remaining ECM
inputs. The fault is indicated by illumination of the
malfunction indicator lamp (MIL). ECM diagnostics
also uses heated oxygen sensors to detect catalyst
damage, misfire and fuel system faults.
Idle Air Control Valve (M112)
The Idle Air Control Valve (M112) controls the idle
speed of the engine by moving the plunger a set
distance, known as a step. Fully open is zero steps
and fully closed is 180 steps. The motor moves each
step by sequentially changing the polarity to each of
the two coils.
thats from rave and it says it will idle then die??? which seems to be on the lines of whats hapening????
.i understand over buckles,just concerned over the maf sensor and ****e wiring.
