Sensors

Sensors

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.

Engine Coolant Temperature Sensor (X126)
The sensor contains two thermistors with negative temperature CO-efficient, i.e. the resistance of the metal strips varies with temperature. The Engine Coolant Sensor (X126) 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.

Crankshaft Position Sensor (X250)
The Engine Control Module (ECM) (Z132) uses the signal produced by the Crankshaft Position (CKP) Sensor to determine the exact position of the crankshaft to enable accurate ignition and fuel injection timing. The ECM also determines engine speed at any particular instance through the analysis of the frequency of fluctuations induced in the CKP sensor as the teeth of the reluctor ring pass by the sensor tip.

Camshaft Position Sensor (Z262)
The CMP sensor is a Hall effect sensor which produces four pulses for every two engine 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 synchronization.

Mass Air Flow Sensor (X105)
The Mass Air Flow Sensor (X105) utilizes a 'hot film' element contained in the intake air tube to monitor the mass flow of the air stream drawn into the engine. It contains two sensing elements: one element is controlled at ambient temperature, while the other is heated to 200° C/ 390° F above the ambient temperature. The air flow passes the heated element and cools it down therefore lowering the resistance of the hot film element. In order to maintain a constant temperature the circuit to the heated element has to supply more current. The measured air mass flow is used by the ECM (Z132) to determine fuel quantity to be injected in order to maintain a stoichiometric air/fuel mixture for optimum engine performance and low emissions.

Throttle Position Sensor (X171)
This sensor is a variable resistor which determines throttle angle position and angular velocity. The signal is used by the ECM (Z132) to calculate fuel injection duration under various operating conditions. The closed idle switch position is used for idle speed control in conjunction with road speed. 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 revolve 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 ceramic body of zirconium and yttrium which is coated with gas-permeable platinum. If the sensor reaches sufficiently high temperatures (above 350° C/660° F) it generates a voltage which is proportional to the oxygen content in the exhaust stream in comparison with the ambient oxygen content. From this value the ECM (Z132) can 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 cataly.These are used to determine whether the catalysts are operating efficiently.