All of the sensors and input switches can be diagnosed with a scan tool. The following is a short description of how the sensors and the switches can be diagnosed with the scan tool. The scan tool can also be used to compare the values of a normal running engine with the engine that is being diagnosed.

The scan tool displays if cruise control is being used. When cruise control is activated, the cruise control module sends a ground signal to the PCM indicating that cruise module is in control of throttle controls. The PCM uses this input to vary transmission controls as needed.

A scan tool displays the engine temperature in degrees Celsius. After the engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens. If the engine has not been run for several hours, or overnight, the ECT and the intake air temperature should be close to each other. A hard fault in the ECT sensor circuit should set either a DTC P0117 or DTC P0118. The DTC tables also contain a table to compare the sensor resistance values relative to temperature.

A scan tool displays the temperature of the air entering the engine, which should be close to the ambient air temperature when the engine is cold and rise as underhood temperature increases. If the engine has not been run for several hours, or overnight, the ECT and the IAT should be close to each other. A fault in the IAT sensor circuit should set either a DTC P0112 or DTC P0113. The DTC tables also contain a table to compare the sensor resistance values relative to temperature.

A scan tool has several parameters that indicate the state of the exhaust gases: O2S 1 voltage, short term fuel trim, and long term fuel trim. A problem in the O2S 1 circuit should set a DTC P0134, open circuit, or DTC P0131, lean exhaust indication, or DTC P0132, rich exhaust indication. A malfunctioning or lazy sensor will set a DTC P0133, slow response, or a DTC P1133, insufficient switching.

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, only after the catalytic converter. This voltage ranges from approximately 0.1 volt (high oxygen - lean mixture) to 0.9 volt (low oxygen - rich mixture). Unlike the O2S 1, with a good catalytic converter, the HO2S 2 is normal when the activity appears lazy or inactive. The PCM compares readings from both the front O2S 1 and the HO2S 2 to determine the catalyst efficiency and will illuminate the MIL if this efficiency falls below a calibrated level.

A scan tool displays throttle position in volts. The scan tool should display 0.20 volt to 0.90 volt with the throttle closed and the ignition on. The voltage should increase at a steady rate as the throttle opens. Voltage should be near 5.0 volts at wide open throttle.

A scan tool also has the ability to display the throttle angle and should display 0 percent when the throttle is closed, and increase smoothly to 100 percent at wide open throttle (WOT). The powertrain control module (PCM) has the ability to auto-zero the TP sensor voltage if the voltage is less than about 0.90 volt (900 mV). This means that any voltage less than 0.90 volt will be determined by the PCM to be 0 percent throttle. A malfunction in the TP sensor or the circuit should set a DTC P0122 or P0123. A stuck TP sensor will set a DTC P0105.

A scan tool displays manifold pressure in kPa and MAP sensor signal voltage. Low pressure (high vacuum) displays a low voltage while a high pressure (low vacuum) displays a high voltage. A malfunction in the MAP sensor circuit should set a DTC P0107 or P0108 and using the applicable table will lead to the cause of the problem. A DTC P0108 may be set if misfire or a rough or unstable idle exists. A DTC P0105 will set for a MAP sensor that intermittently sends a zero voltage signal to the PCM. The Manifold Absolute Pressure Sensor Output Diagnosis can also be used to diagnose the MAP sensor.

A scan tool km/h MPH display should closely match the speedometer reading with drive wheels turning. A malfunction in the vehicle speed sensor (VSS) circuit will set a DTC P0502. Refer to DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input in Automatic Transmission.

A scan tool displays A/C refrigerant pressure in psi. The sensors range and corresponding display should be in the range of 0 to 450 psi. A sensor or circuit problem should set DTC P0530. A faulty ground at the sensor will result in a fixed high pressure value on the scan tool display.

This signal is called a 7X reference signal because a pulse occurs 7 times per crankshaft revolution.

The PCM uses this signal from the electronic ignition control module (ICM) to calculate engine RPM. A scan tool has 2 displays based on this input. One indicates crank RPM or simply that the PCM is receiving the 7X reference pulses while cranking. The other indicates engine RPM while the engine is running. If the PCM receives an intermittent signal from the CKP, then the CKP Resync Counter will increment. More information about this signal may be found in Electronic Ignition (EI) System Description .

The camshaft position sensor (CMP) is used to indicate camshaft position so that the powertrain control module (PCM) can fuel the engine sequentically and determine which cylinder is misfiring when misfire is present. If the PCM receives an intermittent signal from the CMP, then the CMP Resync Counter will increment. In order to set a DTC, the PCM must see a minimum number of resync's within a maximum time.

The scan tool displays oil pressure as Low or OK.

The PCM monitors the engine oil pressure continuously. If the oil pressure switch indicates low oil pressure at any time, the PCM will send information through serial data to the body control module (BCM) to turn on the Low Oil Pressure telltale located on the instrument panel cluster (IPC). If the engine oil pressure drops below approximately 13.8 kPa. (2 psi.) when the engine is running, the Low Oil Pressure telltale will illuminate.

The scan tool displays Gen. L Lamp as Active or Inactive.

The PCM can use the L circuit to control generator operation during starting. If the PCM is disabling the generator, the scan tool will display Active, or the disable operation of the generator is active. The PCM also supplies about 5 volts through the L circuit to the generator. If the generator becomes inoperative, the PCM senses the malfunction through the L circuit and commands the body function controller (BFC) will tell the IPC to turn on the volts telltale lamp.

The scan tool displays Gen. PWM in percentage.

The PCM monitors the duty cycle of the generator through the PWM. As the generator load increases, the PCM can adjust idle speed accordingly. If the body control module (BCM) does not see any activity from the F circuit, the BCM will tell the IPC to turn on the volts telltale lamp.

The scan tool displays fuel tank pressure in volts and inches of water per second.

The fuel tank pressure sensor is similar to the manifold absolute pressure (MAP) sensor. The sensor 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 when the fuel cap is removed, the output voltage of the sensor will be from 1.3 to 1.7 volts.

The PCM uses the fuel level input to determine the expected amount of vapor pressure or vacuum to expect within the fuel tank. The scan tool can displays fuel level in percent for diagnostic purposes. A DTC P0461 will be set if the PCM does not sense a change in the fuel level after a certain time.