Part of Lesson Plan: **Typical Computerized Engine Control Operation (updated) by Sergio Marquez

Activity Overview / Details

Have students follow along using the textbook ( Thomson Delmar Learning, "Automotive Technology: A Systems Approach," 4th edition ), pages 830-837.

Start by explaining that there are 10 primery input sensors, and they are:

Engine coolant Temperature (ECT) Sensor: This sensor inputs to the pcm at what temperature the engine is at, by reading the temperature of the coolant, and you can find this sensor around the thermostat housing. See fig.  33-4.                                                                     

Barometric  Pressure (BARO) and Manifold Absolute Pressure (MAP) Sensors: This sensor monitors engine vacuum for the ECM/PCM to adjust air/fuel mixture and timing at different altitudes and engine load conditions, and you can find this sensor on the intake manifold or around the engine with a vacuum hose going to it from the intake manifold. See fig. 33-8.

Engine Position Sensors: This sensor inputs to the computer the speed of the engine and when the piston in each cylinder is at Top Dead center (TDC).   The input is critical for adjusting the timing and the fuel injection delivery. and you can find this sensor in front of the engine near the crankshaft pully. See fig. 33-5.

Engine Speed Sensor: Similar to the engine position sensor, the information from this sensor may be used by the ecm/pcm computer for determining Ignition timing (Advance), fuel delivery, emission control, torque converter clutch operation, and engine idle speed. You can find this sensor anywhere close to the crankshaft. See fig. 33-5.

Intake Air Temperature (IAT) Sensor: This sensor is a thermistor. Its resistance decreases as intake air temperature increases and increases when the intake air temperature decreases. The ecm/pcm uses this input to help calculate fuel delivery. Cold air is denser; therefore, a richer air/fuel mixture is required, and warmer air leaner air/fuel mixture. You can find this sensor on the intake air duct before the Mass Air Flow Sensor (MAF). See fig. 33-6.

Knock Sensor (KS): The knock sensor sends a signal to the ecm/pcm if a detonation is occurring in the cylinders. In turn, the computer retards the timing to avoid the knock. You can find this sensor on the engine block near the middle cylinders. See fig. 33-7.

Mass Air Flow (MAF) Sensor: This sensor measures the flow of air entering the engine. This measurement of airflow is a reflection of engine load (throttle opening and air volume), This measurement of  air entering the engine determines the 14.7 parts of air to 1 part of fuel ratio. There are three types of (MAF) sensors:  the vane-type, heated resister-type, and the hot wire -type. You can find this sensor on the intake air duct after the intake Air Temperature (IAT) Sensor  and before the throttle plate. See fig. 33-6.

Oxygen Sensor (O2S):   The oxygen sensor, or lambda sensor, as it is referred to on many import vehicles, is the key sensor in calculating and maintaining a balanced air/fuel mixture under all load conditions. There is one (O2S) or as much as six (O2S) found on the latest vehicles, there are two types and they are, single wire (O2S) and four wire (HOS). You can find this sensor on the exhaust manifold, exhaust pipe, and before and after the catalytic converter. See fig. 33-9.

Throttle Position Sensor (TPS): All engines with electronic fuel injection and engines with carburator feed back systems use a (TPS) to inform the ecm/pcm of how fast the throttle is opening and at what position it's at.  For example, closed or idle, cruise speed, or wide open throttle.  It cross references this information with other sensors to verify the drivers intentions. You can find this sensor on the throttle body opposite of the throttle cam. See fig. 33-10.

Vehicle Speed Sensor (VSS) : This sensor informs the ECM/PCM the vehicle's speed in miles per hour. This input controls when the torque converter clutch in the transmission locks up and also is used to control the cruise control, EGR flow, and canister purge (EVAP). You can find this sensor on the transmission close to the output shaft. See fig. 33-11.