The Engine Sensor Ensures Normal Operations

Most sensors will generate digital voltage signals corresponding to their monitoring functions.

The new engine equipped with electronic fuel injection, computerized fuel management and ignition has a large number of sensors that can monitor everything that happens under the hood. Most sensors will generate digital voltage signals corresponding to their monitoring functions.

All these sensor data will be fed back to the powertrain control module (PCM) so that it can make the necessary key decisions to keep the engine running at the best efficiency. Among all sensors, the following five are usually the most critical:

● Crankshaft position (CKP) sensor-Engines equipped with distributor-less ignition systems have Hall effect or magnetic crankshaft position sensors, which can generate trigger signals for the ignition system. This signal will also tell PCM the engine speed (RPM signal) and let PCM know the relative position of the crankshaft. Crankshaft position is very important for calculating fuel injection and ignition timing. On vehicles equipped with variable valve timing (VVT), crankshaft sensor and cam position sensor signals are also used to adjust cam timing. If the crankshaft sensor fails, the engine will not start or run. The sensor is usually located near the crankshaft pulley/balancer at the front of the engine or in the middle of the engine block.

● Engine coolant temperature (ECT) sensor-This sensor monitors the temperature of engine coolant so that PCM can adjust the fuel mixture and ignition timing when the engine is warm-up. Engine temperature is also used as a reminder for various emission control functions. If the coolant sensor reading is inaccurate, it may prevent the engine from entering "closed loop" operation, in which PCM uses the signal from the oxygen sensor to adjust the fuel mixture. This may lead to excessive fuel, increased fuel consumption and increased emissions. The coolant sensor is usually located near the thermostat housing on the engine.

● Mass Air Flow (MAF) sensor-This sensor tells PCM how much air is flowing into the engine. Air flow is a key boundary because it is used to calculate the air/fuel mixture. Most MAF sensors use heated wires or filaments to sense airflow. Dirt or fuel varnish contamination of sensor elements can lead to incorrect readings, which may set codes and/or disrupt engine operation. Cleaning MAF sensor with aerosol electronic cleaner can usually restore normal operation. The MAF sensor is located between the air cleaner housing and the throttle body. Some engines do not use MAF sensors, but use inputs from crankshaft, ambient temperature, coolant temperature, throttle and manifold absolute pressure (MAP) sensors to estimate airflow.

Oxygen (O2) sensor or air/fuel (A/F) sensor-O2 sensor monitors unburned oxygen in exhaust gas and generates a "rich" or "lean" voltage signal, which PCM uses to control the air/fuel mixture. A/F sensor is a smarter version of standard O2 sensor, which can tell PCM the accurate air/fuel ratio. O2 sensors or A/F sensors are located in the exhaust manifold (one for each cylinder bank and sometimes even two). On vehicles equipped with OBD II in 1996 and later, the "downstream" O2 sensor is located in or behind the catalytic converter to monitor the converter efficiency. O2 sensor or A/F sensor problems will not stop the engine from running, but they will lead to fuel mixing problems, thus increasing fuel consumption and emissions.

● Throttle Position (TPS) sensor-This sensor is installed on the shaft of the throttle body to monitor the relative opening of the throttle. PCM uses this information and inputs from MAP and/or MAF sensors to estimate engine load for fuel concentration and timing adjustment. Worn TPS sensors may cause flat spots or hesitation when accelerating. On vehicles equipped with electronic throttle control, there are usually two TPS sensors and a pair of position sensors on the accelerator pedal. The position sensor on the accelerator pedal tells PCM how much throttle should be given to the engine when the driver steps on the accelerator. The TPS sensor on the throttle tells PCM how far the throttle is opened or closed according to PCM's command. The problem here may cause the throttle to fail to open, or even cause unexpected acceleration.