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h32 temperature sensor.pdf

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H32 TEMPERATURE SENSOR
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Temperature Sensors The ECM needs to adjust a variety of systems based on temperatures. It is critical for proper operation of these systems that the engine reach operating temperature and the temperature is accurately signaled to the ECM. For example, for the proper amount of fuel to be injected the ECM must know the correct engine temperature. Temperature sensors measure Engine Coolant Temperature (ECT), Intake Air Temperature (IAT) and Exhaust Recirculation Gases (EGR), etc. TEMPERATURE SENSORSPage 1 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Engine Coolant Temperature (ECT) Sensor The ECT responds to change in Engine Coolant Temperature. By measuring engine coolant temperature, the ECM knows the average temperature of the engine. The ECT is usually located in a coolant passage just before the thermostat. The ECT is connected to the THW terminal on the ECM. The ECT sensor is critical to many ECM functions such as fuel injection, ignition timing, variable valve timing, transmission shifting, etc. Always check to see if the engine is at operating temperature and that the ECT is accurately reporting the temperature to the ECM. Intake Air Temperature (IAT) Sensor The IAT detects the temperature of the incoming air stream. On vehicles equipped with a MAP sensor, the IAT is located in an intake air passage. On Mass Air Flow sensor equipped vehicles, the IAT is part of the MAF sensor. The IAT is connected to the THA terminal on the ECM. The IAT is used for detecting ambient temperature on a cold start and intake air temperature as the engine heats up the incoming air. NOTE: One strategy the ECM uses to determine a cold engine start is by comparing the ECT and IAT signals. If both are within 8'C (15'F) of each other, the ECM assumes it is a cold start. This strategy is important because some diagnostic monitors, such as the EVAP monitor, are based on a cold start. TEMPERATURE SENSORSPage 2 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Exhaust Gas Recirculation (EGR) Temperature Sensor The EGR Temperature Sensor is located in the EGR passage and measures the temperature of the exhaust gases. The EGR Temp sensor is connected to the THG terminal on the ECM. When the EGR valve opens, temperature increases. From the increase in temperature, the ECM knows the EGR valve is open and that exhaust gases are flowing. TEMPERATURE SENSORSPage 3 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.ECT, IAT, & EGR Temperature Sensor Operation Though these sensors are measuring different things, they all operate in the same way. From the voltage signal of the temperature sensor, the ECM knows the temperature. As the temperature of the sensor heats up, the voltage signal decreases. The decrease in the voltage signal is caused by the decrease in resistance. The change in resistance causes the voltage signal to drop. The temperature sensor is connected in series to a fixed value resistor. The ECM supplies 5 volts to the circuit and measures the change in voltage between the fixed value resistor and the temperature sensor. When the sensor is cold, the resistance of the sensor is high, and the voltage signal is high. As the sensor warms up, the resistance drops and voltage signal decreases. From the voltage signal, the ECM can determine the temperature of the coolant, intake air, or exhaust gas temperature. The ground wire of the temperature sensors is always at the ECU usually terminal E2. These sensors are classified as thermistors. Temperature Sensor Diagnostics Temperature sensor circuits are tested for: ? opens. ? shorts. ? available voltage. ? sensor resistance. The Diagnostic Tester data list can reveal the type of problem. An open circuit (high resistance) will read the coldest temperature possible. A shorted circuit (low resistance) will read the highest temperature possible. The diagnostic procedure purpose is to isolate and identify the temperature sensor from the circuit and ECM. High resistance in the temperature circuit will cause the ECM to think that the temperature is colder than it really is. For example, as the engine warms up, ECT resistance decreases, but unwanted extra resistance in the circuit will produce a higher voltage drop signal. This will most likely be noticed when the engine has reached operating temperatures. Note that at the upper end of the temperature/resistance scale, ECT resistance changes very little. Extra resistance in the higher temperature can cause the ECM to think the engine is approximately 20'F = 30'F colder than actual temperature. This will cause poor engine performance, fuel economy, and possibly engine overheating. TEMPERATURE SENSORSPage 4 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Solving Open Circuit Problems A jumper wire and Diagnostic Tester are used to locate the problem in an open circuit. TEMPERATURE SENSORSPage 5 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Solving Shorted Circuit Problems Creating an open circuit at different points in the temperature circuit will isolate the short. The temperature reading should go extremely low (cold) when an open is created. TEMPERATURE SENSORSPage 6 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.ASSIGNMENT NAME: ___________________________ 1. List the three types of temperature sensors used and explain the function of each? 2. Temperature sensors are actually ______________? 3. Draw a sample temperature sensor circuit. (Label all parts) 4. The ECT us used by the computer to control what functions? 5. What PCM strategy is used when both the IAT and ECT are within 15’F of each other? 6. Temperature sensors are tested for: 7. Describe the procedure of testing a temperature sensor. TEMPERATURE SENSORSPage 7 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
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