Engine Controls Component Descriptions. Generic Unit Repair 2008

For 1990-2009 cars only

Makes 🢒 Generic 🢒 2008 🢒 Unit Repair 🢒 Engine 🢒 Engine Controls and Fuel - LS Engines 🢒 Engine Controls Component Descriptions

All of the sensors and the input switches can be diagnosed with the use of a scan tool. The following is a short description of the sensors and switches. The scan tool can also be used in order to compare the values for a normal running engine with the engine being diagnosed.

Camshaft Position Sensor (CMP)

The camshaft position (CMP) sensor is a 3-wire sensor that provides a digital output signal. The CMP harness connector 1 consists of the engine control module (ECM) supplied 5-volt reference circuit, a low reference circuit between the CMP sensor and the ECM, and an output signal circuit from the CMP sensor to the ECM. The CMP sensor detects magnetic flux changes between the teeth and slots on the 4-tooth reluctor wheel. The CMP sensor provides a digital ON/OFF DC voltage of varying frequency, with 4 varying width output pulses, per each camshaft revolution. The frequency of the CMP sensor output signal depends on the speed of the camshaft. The ECM will recognize the narrow and wide tooth patterns to identify camshaft position, or which cylinder is in compression and which is in exhaust. The information is then used to determine the correct time and sequence for fuel injection and ignition spark events. The ECM also uses the CMP sensor output signal to determine the camshaft relative position to the crankshaft position.

Crankshaft Position Sensor (CKP)

The crankshaft position (CKP) sensor is a 3-wire sensor that provides a digital output signal. The circuits consist of an engine control module (ECM) supplied 5-volt reference circuit, a low reference circuit between the CKP sensor and the ECM, and an output signal circuit from the CKP sensor to the ECM. The CKP sensor detects magnetic flux changes of the teeth and slots of the 58-tooth reluctor on the crankshaft. The CKP sensor provides an ON/OFF DC voltage of varying frequency, with 58 output pulses per each crankshaft revolution. The frequency of the CKP sensor output signal depends on the speed of the crankshaft. The CKP sensor sends a digital square wave signal, which represents an image of the teeth on the reluctor wheel, to the ECM. The 12 degree reference gap on the reluctor wheel is used to identify crankshaft position. The CKP information, along with the camshaft position (CMP) sensor information is used to determine the correct time and sequence for fuel injection, ignition spark events, detect cylinder misfire, and the camshaft to crankshaft relative position.

Engine Coolant Temperature (ECT) Sensor


(1)	ECT Electrical Connector
(2)	Connector Tab
(3)	Engine Coolant Temperature (ECT) Sensor

The engine coolant temperature sensor is a thermistor (a resistor which changes value based on temperature) mounted in the left cylinder head. Low coolant temperature produces a high resistance, 100,000 ohms at -38°C (-39°F), while high temperature causes low resistance, 70 ohms at 130°C (266°F).

The ECM supplies a 5.0 volt signal to the ECT sensor. The ECM measures the voltage drop across the sensor. The voltage will be high when the engine is cold. The voltage will be low when the engine is hot. The ECM calculates the engine coolant temperature by measuring the voltage. The engine coolant temperature is a critical input for the ECM controls.

The scan tool displays engine coolant temperature in degrees. When the engine starts the engine coolant temperature should rise steadily to approximately 90°C (194°F) then stabilize when the thermostat opens. The engine coolant temperature and intake air temperature parameter displays should be close to each other if the engine has not been run for several hours (overnight).

Heated Oxygen Sensors (HO2S)


(1)	Four Wire In-Line Connector
(2)	Heater Termination
(3)	Water Shield Assembly
(4)	Sensor Lead
(5)	Flat Seat Shell
(6)	Seat Gasket
(7)	Outer Electrode and Protective Coating
(8)	Rod Heater
(9)	Inner Electrode
(10)	Zirconia Element
(11)	Insulator
(12)	Clip Ring
(13)	Gripper

The Heated Oxygen Sensors are mounted in the exhaust system where they can monitor the oxygen content of the exhaust gas stream. The oxygen present in the exhaust gas reacts with the sensor to produce a voltage output. This voltage should constantly fluctuate from approximately 100 mV (high oxygen content=lean mixture) to 900 mV (low oxygen content=rich mixture). The heated oxygen sensor voltage can be monitored with a scan tool. By monitoring the voltage output of the oxygen sensor, the ECM calculates the pulse width command to operate the fuel injectors (lean mixture/low HO2S voltage=rich command, rich mixture/high HO2S voltage=lean command).

Intake Air Temperature (IAT) Sensor

The intake air temperature (IAT) sensor is integrated within the Mass Air Flow (MAF) sensor. The IAT sensor is a thermistor which changes value based on the temperature of air entering the engine. Low temperature produces a high resistance, 100,000 ohms at -38°C (-39°F). A high temperature causes low resistance, 70 ohms at 130°C (266°F). The ECM supplies a 5 volt signal to the sensor. The ECM measures the voltage drop across the sensor. The voltage will be high when the incoming air is cold, and low when the air is hot. The ECM calculates the incoming air temperature by measuring the IAT voltage. The IAT sensor signal is used to adjust spark timing according to incoming air density.

The scan tool displays the temperature of the air entering the engine, which should be close to ambient air temperature when the engine is cold. The temperature should rise as under-hood temperature increases. The engine coolant temperature and intake air temperature parameter displays should be close to each other if the engine has not been run for several hours (overnight).

Knock Sensors (KS)

A Knock Sensor (KS) system is used in order to control spark knock. The KS system is designed to retard spark timing up to 20 degrees in order to reduce spark knock in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.

The knock sensor system is used to detect engine detonation. The knock sensors produce an AC voltage which is sent to the ECM. The ECM retards the spark timing based on signals from the KS sensors. The amount of AC voltage produced by the sensors is determined by the amount of knock. The ECM then adjusts the Ignition Control (IC) to reduce the spark knock.

Mass Air Flow (MAF) Sensor

The Mass Air Flow (MAF) sensor measures the amount of air which passes through it. The ECM uses this information to determine the operating condition of the engine in order to control the fuel delivery. A large quantity of air indicates acceleration. A small quantity of air indicates deceleration or idle.

The scan tool reads the MAF value and displays it in grams per second (g/s). The MAF sensor displays between 6 - 9 g/s at idle on a fully warmed up engine. The MAF sensor values should change rather quickly on acceleration, but the MAF sensor values should remain fairly stable at any given engine speed.

Manifold Absolute Pressure (MAP) Sensor

The Manifold Absolute Pressure (MAP) sensor (1) responds to changes in the intake manifold pressure. The pressure changes as a result of engine load and speed. The map sensor converts this to a voltage output.

A closed throttle on engine coast down produces a relatively low MAP output voltage. A wide open throttle produces a high MAP output voltage. This high output voltage is produced because the pressure inside the manifold is the same as outside the manifold. The MAP is inversely proportional to what is measured on a vacuum gauge. The MAP sensor is used for the following:

•	Altitude determination.

•	Ignition timing control.

•	Speed density fuel management default.

Vehicle Speed Sensor (VSS)

The Vehicle Speed Sensor (VSS) is a pulse counter type input that informs the ECM how fast the vehicle is traveling. The VSS system uses an inductive sensor mounted in the tail housing of the transmission and a toothed reluctor wheel on the tail shaft. The teeth of the reluctor wheel alternately interfere with the magnetic field of the sensor creating an induced voltage pulse as the reluctor rotates.

The VSS produces an AC voltage signal that increases with vehicle speed. The ECM processes this signal and sends it to the bulkhead connector.