Sensors

ENGINE FUEL TEMPERATURE SENSOR (X128)
This is a resistive sensor, located on the fuel rail and measuring the temperature of the rail rather than the fuel. The signal is used to increase the injection pulse times when undergoing hot restarts. When the fuel is hot, vaporisation occurs in the rail and a "bubble" could form within the injectors. Increasing the pulse times flushes the "bubbles" away and cools the fuel rail with fuel from the tank.

KNOCK SENSORS (X309, X310)
The knock sensor is a "Piezo-electric accelerometer," i.e. it produces an output voltage proportional to mechanical vibration produced by the engine. The Engine Control Module (ECM) (Z132) receives the signal, filters out any noise and calculates if the engine is knocking. Due to the cam and crank signals supplying information regarding the position of the engine in it's cycle, the ECM (Z132) can work out exactly which cylinder is knocking and retards the ignition on that particular cylinder until the knock disappears. It then advances the ignition again to find the optimum ignition point for that cylinder for those conditions (i.e. fuel type, air temperature etc.). The ECM (Z132) will be able to adjust cylinder timing for knock simultaneously, so that all eight cylinders could have different advance angles at the same time.

COOLANT TEMPERATURE SENSOR (X126)
A temperature dependant resistive metal component is the major constituent of this sensor, i.e. the resistance of the metal strip varies quite considerably with temperature. The coolant sensor signal is vital to correct engine operation, as the injected fuel quantity is dependant upon the engine temperature, i.e. richer mixture at low temperatures.

INTAKE AIR TEMPERATURE SENSOR (X311)
This is a resistive sensor, i.e. the change in resistance is related to change in air temperature. The signal from the Intake Air Temperature Sensor (X311) is used to retard the ignition timing if the air temperature rises above 55°C.

CRANKSHAFT POSITION SENSOR (X250)
The Crankshaft Position Sensor (X250) is a very important sensor, as the signal it produces tells the ECM (Z132) that the engine is turning, how fast it is turning and at which stage the engine is at in the cycle. The crank signal is the basis of the fuel injection and coil firing times.

CAMSHAFT POSITION SENSOR (Z262)
This is a Hall Effect sensor producing one pulse for every two revolutions. The Signal is used in two areas: Injector timing corrections for fully sequential fuelling and active knock control.

Camshaft operation is essential to continue normal ignition, i.e. actuate the fuel injectors in the normal sequential order, timing the injection correctly with respect to top dead centre. In this way the sequential fuelling will either be correct, or one engine revolution out of synchronisation.

MASS AIR FLOW SENSOR (X105)
The sensing element of a Mass Air Flow Sensor (X105) is a "hot wire anomometer" consisting of one heated wire. 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.

North American vehicles have two extra heated oxygen sensors mounted one after each catalyst. These are used to determine whether the catalysts are operating efficiently.