start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 55, the reader should be able to: • • • • Prepare for ASE Engine Performance (A8) certification test content area “E” (Computerized Engine Controls Diagnosis and Repair) Explain the purpose and function of the ECT and IAT temperature sensors Describe how to test temperature sensors Discuss how MAP sensors work Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 55, the reader should be able to: • List the methods that can be used to test MAP • • • • sensors List how the operation of the MAP sensor affects vehicle operation Discuss MAP sensor rationality tests Discuss how MAF sensors work List the methods that can be used to test MAF sensors Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 55, the reader should be able to: • List how the operation of the MAF sensor affects vehicle operation Discuss MAF sensor rationality tests Discuss how oxygen sensors (O2S) work • • • Describe the symptoms of a failed oxygen sensor Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: barometric manifold absolute pressure (BMAP) • barometric pressure (BARO) sensor • bias voltage cylinder head temperature (CHT) • closed-loop operation • cross counts engine coolant temperature (ECT) false air • false lean indication • false rich indication • fuel trim hot film sensor • hot wire sensor • intake air temperature (IAT) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: Karman vortex sensor lean air–fuel ratio sensor (LAF) • linear air–fuel ratio sensor manifold absolute pressure (MAP) • mass airflow sensor (MAF) negative temperature coefficient (NTC) open-loop operation • oxygen sensor (O2S) piezoresistivity • pressure differential Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: skewed • speed density tap test • throttle-body temperature (TBT) • throttle position (TP) • transmission fluid temperature (TFT) • transmission oil temperature (TOT) vacuum • vane airflow sensor (VAF) wide-band O2S Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ENGINE COOLANT TEMPERATURE SENSORS Computer­equipped vehicles use an engine coolant temperature  (ECT) sensor. The computer controls spark timing and fuel  mixture, and needs to know the engine temperature.  An engine coolant  temperature sensor  (ECT) screwed into  the coolant passage  will provide this  information.  Figure 55–1 A typical engine coolant temperature (ECT) sensor ECT sensors are located near the thermostat housing on most engines Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Ignition timing can be tailored to coolant  temperature. A hot engine  cannot have the spark timing as far advanced as can a cold engine.  The ECT sensor is also used as an input for: Idle air control (IAC) position Oxygen sensor closed­loop  status Canister purge on/off times Idle speed Coolant temperature sensors are constructed of a semi­conductor  material that decreases in resistance as sensor temperature increases If the sensor has a poor connection (high resistance) the computer  will supply a richer­than­normal mixture based on resistance of  the coolant sensor. Poor fuel economy and a possible­rich code  can be caused by a defective sensor or high resistance in wiring.    If too low a resistance, a leaner­than­normal fuel mixture would be  supplied to the engine Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 55–2 A typical ECT sensor temperature versus voltage curve Coolant sensors have  very high resistance  when the coolant is cold  and low resistance when  the coolant is hot.  This is referred to as a  negative temperature  coefficient (NTC), which is opposite to the  situation with most other  electrical components.  10 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 CAUTION: Do not spray any silicone spray near the engine where the  engine vacuum could draw the fumes into the engine. This can also cause  silica damage to the oxygen sensor. Also be sure that the silicone sealer  used for gaskets is rated oxygen sensor safe Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 16 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 What is Lambda? An oxygen sensor is also called a lambda sensor because the voltage changes at the air–fuel ratio of 14.7:1, which is the stoichiometric rate for gasoline If this mixture of gasoline and air is burned, all of the gasoline is burned and uses all of the oxygen in the mixture This exact ratio represents a lambda of 1.0 the mixture is richer (more fuel or less air), the number is less than 1.0, such 0.850 If the mixture is leaner than 14.7:1 (less fuel or more air), the lambda number is higher than 1.0, such as 1.130 Often, the target lambda is displayed on a scan tool Figure 55–46 The target lambda on this vehicle is slightly lower than 1.0 indicating that the PCM is attempting to supply the engine with an air–fuel mixture that is slightly richer than stoichiometric Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 16 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OXYGEN-SENSOR RELATED DIAGNOSTIC TROUBLE CODES Diagnostic trouble codes (DTCs) associated with the oxygen sensor: See the chart on Page 654 of your textbook.  Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 16 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Throttle Position Sensor Diagnosis Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 16 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE TPS Diagnosis Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) 16 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE TPS Diagnosis Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) 16 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Oxygen Sensor Testing Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 17 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Oxygen Sensor Testing Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) 17 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Oxygen Sensor Testing Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) 17 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY All temperature sensors decrease in resistance as the  temperature increases. This is called negative temperature  coefficient (NTC) The ECT and IAT sensors can be tested visually, as well as by  using a digital multimeter or a scan tool A throttle position (TP) sensor is a three­wire variable resistor  called a potentiometer The three wires on the TP sensor include a 5­volt reference  voltage from the PCM, plus the signal wire to the PCM, and a  ground, which also goes to the PCM 17 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) The TP sensor signal voltage should be about 0.5 volt at idle  and increase to about 4.5 volts at wide­open throttle (WOT) A TP sensor can be tested using a digital multimeter, a digital  storage oscilloscope (DSO), or a scan tool Pressure below atmospheric pressure is called vacuum and is  measured in inches of Mercury A manifold absolute pressure sensor uses a perfect vacuum  (zero absolute pressure) in the sensor to determine the  pressure 17 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Three types of MAP sensors include: • Silicon­diaphragm strain gauge • Capacitor­capsule design • Ceramic disc design 10 A MAP sensor is used to detect changes in altitude, as well as  check other sensors and engine systems 11 A MAP sensor can be tested by visual inspection, testing the  output using a digital meter or scan tool 17 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) 12 A mass airflow sensor actually measures the density and  amount of air flowing into the engine, which results in  accurate engine control 13 An air vane sensor measures the volume of the air, and the  intake air temperature sensor is used by the PCM to calculate  the mass of the air entering the engine 14 A hot wire MAF sensor uses the electronics in the sensor itself  to heat a wire 70°C above the temperature of the air entering  the engine 17 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) 15 An oxygen sensor produces a voltage output signal based on  the oxygen content of the exhaust stream 16 If the exhaust has little oxygen, the voltage of the oxygen  sensor will be close to 1 volt (1,000 mV) and close to zero if  there is high­oxygen content in the exhaust 17 Oxygen sensors can have one, two, three, four, or more wires,  depending on the style and design 18 A wide­band oxygen sensor, also called a lean air–fuel (LAF)  or linear air–fuel ratio sensor, can detect air–fuel ratios from as  rich as 12:1 to as lean as 18:1 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 17 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 17 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458