PCM Inputs
PCM INPUTS DIAGNOSISAll of the sensors and input switches can be diagnosed by the use of a scan tool. The following is a short description of how the sensors and switches can be diagnosed by the use of the scan tool. The scan tool can also be used to compare the values for a normal running engine with the engine that is being diagnosed.
CRUISE ENGAGED
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.
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
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 (overnight), the ECT and IAT temperatures should be close to each other. A hard fault in the ECT sensor circuit should set either a DTC P0117 or P0118. The DTC tables also contain a table to check for sensor resistance values relative to temperature.
INTAKE AIR TEMPERATURE (IAT) SENSOR
A scan tool displays the temperature of the air entering the engine, which should be close to ambient air temperature when engine is cold, and rise as underhood temperature increases. If the engine has not been run for several hours (overnight), the ECT and lAT temperatures should be close to each other. A fault in the AT sensor circuit should set either a DTC P0112 or DTC P0113. The DTC tables also contain a table to check for sensor resistance values relative to temperature.
OXYGEN SENSOR (O2S 1)
A scan tool has several parameters that indicate the state of the exhaust gases: O2S 1 voltage, S. t fuel trim, and L. T. fuel trim. A problem in the O2S 1 circuit should set a DTC P0134 (open circuit), DTC P0131 (lean exhaust indication), or DTC P0132 (rich exhaust indication). A faulty or lazy sensor will set a DTC P0133 (slow response) or a DTC P1133 (insufficient switching).
REAR HEATED OXYGEN SENSOR (HO2S 2)
The Rear Heated Oxygen Sensor (HO2S 2) is used to monitor the oxygen storage capability of the catalytic converter. Similar to the 02S 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 .1 volt (high oxygen - lean mixture) to .9 volt (low oxygen - rich mixture). Unlike the 02S 1, with a good catalytic converter, the HO2S 2 is normal when its 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.
THROTTLE POSITION (TP) SENSOR
A scan tool displays throttle position in volts. The scan tool should display 0.20 volt to 0.90 volt with the throttle closed (as at idle) and ignition ON. 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% when the throttle is closed, and increase smoothly to 100 % at WOT The Powertrain Control Module (PCM) has the ability to auto-zero the TP sensor voltage if it is below about 0.90 volt (90OmV). This means that any voltage less than 0.90 volt will be determined by the PCM to be 0 % throttle. A fault in the TP sensor or circuit should set a DTC P0122 or P0123. A stuck sensor will set a DTC P0121.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
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 failure in the MAP sensor circuit should set a DTC P01 07 or P01 OS and using the applicable table will lead to the cause of the problem. A DTC P0108 may be set it 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. MAP Sensor Output Check can also be used to check the MAP sensor.
VEHICLE SPEED SENSOR (VSS)
A scan tool MPH display should closely match the speedometer reading with drive wheels turning A fault in the Vehicle Speed Sensor (VSS) circuit will set a DTC P0502. If the vehicle speed is suddenly lost while cruising, the PCM will set a DTC P05O3 and the transmission will default to keep the transmission from suddenly going into first gear.
AC REFRIGERANT PRESSURE SENSOR
A scan tool displays AC refrigerant pressure in psi. The sensor's range and corresponding display should be in the range of 0 to 450 psi. A sensor or circuit problem should set DTC P0530. A poor ground at the sensor will result in a fixed high pressure value on the scan tool display.
CRANKSHAFT ACTIVITY COUNTER
This signal is called a 7X reference signal. it is because a pulse occurs every 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 two 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 System.
CAMSHAFT POSITION (CM P) SENSOR
The Camshaft Position Sensor (CMP) is used to indicate camshaft position so that the Powertrain Control Module (PCM) can 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 5 within a maximum time.
ENGINE OIL LEVEL
The scan tool displays oil level as Low or OK. The PCM checks engine oil level during engine start-up. If the oil level switch indicates low oil level at this time, the PCM will send information through serial data to the Instrument Panel Cluster (I PC) to turn ON the Low Oil Level symbol lamp. Engine oil level is checked only once per ignition cycle and also after the ignition is turned OFF to allow the oil enough time to drain back into the oil pan before making a decision whether the oil is low or not.
ENGINE COOLANT LEVEL
The scan tool displays coolant level as Low or OK. The PCM checks the engine coolant level continuously. if the coolant level switch indicates low coolant level at any time, the PCM will send information through serial data to the Instrument Panel Cluster (IPC) to turn ON the Low Coolant Level symbol lamp.
ENGINE 0IL PRESSURE
The scan tool displays oil pressure as Low or OK. The PCM checks 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 Instrument Panel Cluster (IPC) to turn ON the Low Oil Pressure symbol lamp.
GENERATOR L LAMP CIRCUIT
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 fault through the L circuit and commands the Instrument Panel Cluster (IPC) to turn on the volts telltale.
GENERATOR F FIELD CIRCUIT
The scan tool displays Gen. F Field in percentage. The PCM monitors the duty cycle of the generator through the F circuit. As the generator load increases, the PCM can adjust idle speed accordingly. If the Instrument Panel Cluster (I PC) does not see any activity from the F circuit, the IPC will turn ON the volts telltale.
FUEL TANK VAPOR PRESSURE SENSOR
The scan tool displays fuel tank vapor pressure in volts and inches of water per second.
The fuel tank vapor 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 when the fuel cap is removed, the output voltage of the sensor will be from 1.3 to 1.7 volts.
FUEL LEVEL SENSOR
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 P046O will be set if the PCM does not see a change in the fuel level after a certain time.