The Engine Coolant Temperature (ECT) sensor (3) is a thermistor, a resistor that changes value based on temperature. The ECT is mounted in the engine coolant stream. The ECT sensor's resistance varies with the coolant temperature. Low coolant temperature produces high resistance, approximately 100,000 ohms at -40°C (-40°F), while high temperature causes low resistance, approximately 70 ohms at 130°C (266°F).

The PCM supplies a 5 volt signal to the ECT sensor through a resistor in the PCM and monitors the terminal voltage. This forms a series circuit to ground through the ECT sensor, causing high sensor resistance (low temperature) to result in high PCM terminal voltage. When the resistance of the ECT sensor is low (high temperature), the terminal voltage is reduced. The terminal voltage indicates engine coolant temperature to the PCM.

A hard fault in the ECT sensor circuit should set either a DTC P0117 or P0118. These DTCs indicate a malfunction in the engine coolant temperature circuit. Most such malfunctions can be corrected by either repairing a wiring problem or replacing the sensor. Consult the appropriate DTC table to properly repair any problems with the ECT circuit.

The Intake Air Temperature (IAT) sensor is a thermistor, a resistor which changes value based on the temperature. The IAT sensor measures the temperature of the air entering the engine. Low air temperature produces a high resistance, approximately 100,000 ohms at -40°C (-40°F), while high temperature causes low resistance, approximately 70 ohms at 130°C (266°F). The PCM supplies a 5 volt signal to the IAT sensor through a resistor in the PCM and monitors the terminal voltage. The voltage is high when the intake air is cold, and low when the intake air is hot. By measuring the voltage, the PCM knows the intake air temperature. This air temperature data is used by the PCM in fuel control calculations.

A fault in the IAT sensor circuit should set either a DTC P0112 or DTC P0113.

The oxygen sensor (O2S 1) is mounted in the exhaust system where it can monitor the oxygen content of the exhaust gas stream. The oxygen content in the exhaust reacts with the sensor to produce a voltage output. This voltage ranges from approximately 0.1 volt (high oxygen -- lean mixture) to 0.9 volt (low oxygen -- rich mixture). This voltage can be measured with a scan tool.

By monitoring the voltage output of the O2S 1, the PCM will know what fuel mixture command to give to the injectors.

The O2S 1, if open, should set a DTC P0134. A constant low voltage in the sensor circuit should set a DTC P0131. A constant high voltage in the circuit should set a DTC P0132. DTCs P0131 and P0132 could also be set as a result of fuel system problems. See the DTC tables for conditions that can cause a lean or rich system.

The rear heated oxygen sensor (HO2S 2) is used to monitor the oxygen storage capability of the catalytic converter. Similar to the O2S 1, the HO2S 2 reacts with the oxygen content in the exhaust stream to produce a voltage signal. This voltage ranges from approximately 0.1 volt (high oxygen -- lean mixture) to 0.9 volt (low oxygen -- rich mixture). When the catalytic converter is functioning correctly, the HO2S 2 will be fairly inactive. The PCM compares readings from both the front O2S 1 and the HO2S 2 to determine the catalyst efficiency. The PCM will illuminate the MIL if the catalyst efficiency falls below a calibrated level.

The throttle position (TP) sensor (2) is a potentiometer connected to the throttle shaft on the throttle body. The TP sensor electrical circuit consists of a 5 volt supply line and a ground line, both provided by the powertrain control module (PCM), and a signal line to the PCM. By monitoring the voltage on this signal line, the PCM can calculate throttle position angle in a percentage. As the throttle valve angle is changed (accelerator pedal moved), the output of the TP sensor also changes. At a closed throttle position, the output of the TP sensor is low (approximately 0.6 volt). As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be near 5 volts.

The PCM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor can cause intermittent bursts of fuel from the injectors and an unstable idle, because the PCM thinks the throttle is moving. A high or low voltage problem in the TP sensor circuits should set either a DTC P0122 or DTC P0123. The PCM also has the capability of setting a DTC P0105 if the sensor is reading out of range. Once a diagnostic trouble code is set, the PCM will use a default value for the TP sensor, and some vehicle performance will return.

See Throttle Position Sensor Replacement for replacement of the TP sensor. The TP sensor is not adjustable.

The manifold absolute pressure (MAP) sensor measures the changes in the intake manifold pressure that result from engine load and speed changes and converts this measurement into a voltage output.

The PCM sends a 5 volt reference signal to the MAP sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes. By monitoring the sensor output voltage, the PCM can determine the manifold pressure. A higher pressure, indicating low vacuum and high voltage, requires more fuel, while a lower pressure indicating high vacuum and low voltage, requires less fuel.

A closed throttle when the engine is decelerating produces a relatively low MAP output, while a wide open throttle produces a high output. Manifold absolute pressure is the OPPOSITE of what is measured by a vacuum gauge. When manifold pressure is high, vacuum is low. The MAP sensor also measures barometric pressure under certain conditions, allowing the PCM to automatically adjust for different altitudes.

A high or low voltage fault in the MAP sensor circuit should set a DTC P0107 or DTC P0108. If the MAP sensor sends an intermittent zero voltage signal to the PCM, a DTC P0105 will set.

The vehicle speed sensor (VSS) is a permanent magnet generator in the transaxle. the VSS sends an AC voltage signal to the powertrain control module (PCM), which the PCM converts to kilometers per hour (km/h) and miles per hour (MPH). There are several different types of vehicle speed sensors.

Refer to Automatic Transmission for more information.

The knock sensor (KS) detects abnormal vibration, or spark knock, in the engine. The sensor is mounted in the engine block near the cylinders. The knock sensor produces an AC output voltage that increases with the severity of the knock. This signal voltage is sent to the powertrain control module (PCM). The PCM then adjusts the ignition control (IC) timing to reduce the spark knock.

A fault in the KS circuit will set a DTC P0325.

The air conditioning (A/C) refrigerant pressure sensor provides a signal to the powertrain control module (PCM) which indicates varying high side refrigerant pressure between approximately 0 psi and 450 psi.

The PCM uses the A/C refrigerant pressure sensor input to determine the A/C compressor load on the engine. The PCM uses the information it receives from A/C refrigerant pressure sensor to help control idle speed with the IAC valve.

The A/C refrigerant pressure sensor electrical circuit consists of a 5 volt reference line and a ground line, both provided by the PCM, and a signal line to the PCM. The signal is a voltage that varies from approximately 0.1 volt at 0 psi, to 4.9 volts at 450 psi or more. A problem in the A/C refrigerant pressure circuits or sensor may set a DTC P0530 and will make the A/C compressor inoperative.

The CKP sensor provides a signal to the electronic ignition control module (ICM), which the PCM uses as a reference to calculate RPM and the crankshaft position. A fault in the CKP sensor circuits will cause a DTC P0335.

Important: A Crankshaft Position System Variation Learning Procedure must be performed any time a change is made in the relationship of the crankshaft sensor to the crankshaft. Changing the crankshaft sensor to crankshaft relationship without performing this procedure will cause the PCM to be unable to detect misfire at all speeds and loads accurately. When this occurs, a false misfire DTC may be set. Removing a part for inspection and then reinstalling the same part is considered a disturbance. A false DTC P0300 could be set if this procedure is not performed. Refer to the Crankshaft Position System Variation Learn for the Crankshaft Position System Variation Learning Procedure.

Refer to Electronic Ignition (EI) System Diagnosis for further information.

The camshaft position sensor (CMP) is used in order to correlate the crankshaft to the camshaft position so that the powertrain control module (PCM) can determine which cylinder is ready to be fueled by the injector. The CMP sensor is also used in order to determine which cylinder is misfiring when a misfire is present. If the PCM receives an intermittent signal from the CMP, then the CMP resync counter will increment. When the PCM cannot use the information from the CMP sensor, a DTC is set and the PCM will fuel the engine using the Alternating Synchronous Double Fire (ASDF) method. This sensor has no effect on the electronic ignition (EI) system.

A fault in the CMP sensor circuits will cause a DTC P0341 or P0342.

The fuel tank pressure sensor is similar to the manifold absolute pressure (MAP) sensor. It is used to measure the difference between the air pressure, or vacuum, in the fuel tank and the outside air pressure. The PCM supplies a 5 volt reference and a ground to the sensor and the sensor sends a voltage signal between 0.1 and 4.9 volts back to the PCM. When the air pressure in the fuel tank is equal to the outside air pressure, as it is when the fuel cap is removed, the output voltage of the sensor will be from 1.3 to 1.7 volts.

A fault in the fuel tank pressure sensor will cause a DTC P0452 or P0453.

The fuel level sensor is attached to the modular fuel sender assembly. The resistance of the fuel sensor changes with fuel level by means of a rheostat. The fuel level sensor's range is from 250 ohms with a full tank to 40 ohms with an empty tank. This resistance value is sent to the PCM. The PCM sends the fuel level information to the IPC over Class 2 serial data. The fuel level sensor is also used for evaporative emissions system diagnosis.