Engine Controls Self-Diagnostics - 2.2L & 2.4L: Overview

MODEL IDENTIFICATION

Vehicle and engine model is identified by Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION and ENGINE IDENTIFICATION tables.

Body Code (1)	Model
J	Cavalier & Sunfire
N	Alero & Grand Am
(1) Vehicle body code is 4th character of VIN.

(1)	Vehicle body code is 4th character of VIN.

MODEL IDENTIFICATION

Engine Code (1)	Engine
4	2.2L
T	2.4L
(1) Vehicle engine code is 8th character of VIN.

(1)	Vehicle engine code is 8th character of VIN.

ENGINE IDENTIFICATION

Description

For vehicles designed to run on fuels other than gasoline, some additional procedures may be required to set I/M System Status indicators to YES. Vehicles designed to run on both gasoline and Compressed Natural Gas (CNG) will disable certain diagnostic tests when vehicle is operating on CNG. These vehicles will require operation using gasoline for remaining tests to run. The system set procedures for gasoline vehicles can be used once vehicle is operating on gasoline.

This procedure satisfies enable criteria necessary to execute all monitor diagnostics, and complete trips for those particular diagnostics. When all diagnostic tests have been completed, I/M System Status indicators are set to YES. Perform this test when more than one or all I/M System Status indicators are set to NO.

Ensure vehicle meets the following conditions before performing procedure

Barometric (BARO) pressure is more than 72 kPa.
Engine Coolant Temperature (ECT) is less than 84°F (29°C).
Intake Air Temperature (IAT) is less than 84°F (29°C).
Difference between Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) is 13°F (7°C) or less.
Battery voltage is between 9-16 volts.
Fuel level is 1/4-3/4 tank.

This test should satisfy enable criteria necessary to execute I/M readiness diagnostics for the catalyst system. Test may be used to set I/M SYSTEM STATUS indicators to YES. Ensure vehicle meets requirements listed in enable criteria before performing test.

This test should satisfy enable criteria necessary to execute I/M readiness diagnostics for the evaporative emission system. Test may be used to set I/M SYSTEM STATUS indicators to YES. Ensure vehicle meets requirements listed in enable criteria before performing test.

Purpose of this test is to satisfy enable criteria necessary to execute I/M readiness diagnostics for heated oxygen sensor/oxygen sensor system. Test may be used to set I/M system status indicators to YES. Ensure vehicle meets enable criteria before performing test.

This test is to satisfy enable criteria to execute I/M readiness diagnostics for Oxygen Sensor (O2S) and Heated Oxygen Sensor (HO2S) system. Test may be used to set I/M System Status to YES. Ensure vehicle meets requirements listed in CONDITIONS FOR RUNNING before performing this test. Failure to meet necessary requirements may produce inaccurate test results.

Purpose of this test is to satisfy enable criteria necessary to execute I/M readiness diagnostics for heated oxygen sensor heater system. Test may be used to set I/M system status indicators to YES. Ensure vehicle meets enable criteria before performing test.

PCM supplies a 5-volt reference signal and a ground circuit to both the MAP sensor and TP sensor. MAP sensor returns a signal to PCM relative to intake manifold pressure, and TP sensor returns a signal to PCM relative to throttle plate opening.

PCM can determine if sensors are out of range by comparing sensor values to expected limits predetermined by PCM during all modes of operation. DTC P0105 will set if MAP sensor or TP sensor are out of an expected range as determined by engine calibration.

Powertrain Control Module (PCM) supplies 5 volts on Throttle Position (TP) and Manifold Absolute Pressure (MAP) sensor reference voltage circuits. PCM also supplies a ground circuit to TP and MAP sensors. When throttle is depressed, TP signal voltage rises to approximately 5 volts. As throttle is released, TP signal voltage drops to around 0.6 volt. PCM and the Alternate Fuel Engine Control Unit (AF ECU) monitor TP signal circuit voltage and determine angle (or opening) of throttle plate.

When manifold vacuum is low, MAP signal voltage to approximately 4.5 volts. As manifold vacuum increases, MAP signal voltage drops to around one volt. PCM and AF ECU monitor MAP signal circuit voltage and determine vacuum within intake manifold.

Certain vehicle models will also use MAP sensor to determine barometric pressure when ignition switch is turned ON and engine is not running. This BARO reading may also be updated whenever engine is operated at wide open throttle.

PCM supplies 5 volts to MAP sensor on 5-volt reference circuit. PCM also provides a ground on low reference circuit. MAP sensor provides a signal to PCM on signal circuit which is relative to pressure changes in manifold. PCM should detect a low signal voltage at a low MAP, such as during idle or deceleration. PCM should detect a high signal voltage at a high MAP, such as ignition on, with engine off, or at Wide Open Throttle (WOT). Certain models will also use MAP sensor in order to determine Barometric (BARO) pressure. This occurs when ignition is turned on, with engine off. BARO reading may also be updated whenever engine is operated at WOT. PCM monitors MAP sensor signal for voltage outside of normal range.

Powertrain Control Module (PCM) supplies 5-volt reference and ground to Manifold Absolute Pressure (MAP) sensor. When manifold vacuum is low, MAP signal voltage rises to near 4.5 volts. As manifold vacuum increases, MAP signal voltage drops to around one volt. PCM and Alternate Fuel Engine Control Unit (AF ECU) monitor MAP signal circuit voltage and determine vacuum within intake manifold. Certain vehicle models will also use MAP sensor to determine barometric pressure when ignition is on and engine is off. This BARO reading may also be updated when engine is operated at wide open throttle.

PCM supplies 5 volts to MAP sensor on 5-volt reference circuit. PCM also provides a ground on low reference circuit. MAP sensor provides a signal to PCM on signal circuit which is relative to pressure changes in manifold. PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. PCM should detect a high signal voltage at a high MAP, such as ignition on, with engine off, or at a Wide Open Throttle (WOT). Certain models will also use MAP sensor in order to determine Barometric (BARO) pressure. This occurs when ignition is turned on, with engine off. BARO reading may also be updated whenever engine is operated at WOT. PCM monitors MAP sensor signal for voltage outside of normal range.

Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. IAT sensor measures temperature of air entering engine. PCM supplies 5 volts to IAT signal circuit. When IAT sensor is cold, sensor resistance is high. When air temperature increases, sensor resistance lowers. With high sensor resistance, PCM detects a high voltage on IAT signal circuit. With lower sensor resistance, PCM detects a lower voltage on IAT signal circuit. If PCM detects an excessively low IAT signal voltage, indicating a high temperature, this DTC will set.

Intake Air Temperature (IAT) sensor is a thermistor. IAT sensor has high resistance when cold and low resistance when hot. Powertrain Control Module (PCM) supplies 5 volts and ground IAT sensor. When IAT resistance is high (cold sensor) signal voltage remains near 5 volts. As IAT sensor warms and resistance drops, signal voltage is low. PCM and the Alternate Fuel Engine Control Module (AF ECU) monitor IAT signal circuit voltage to determine temperature of air entering engine.

Intake Air Temperature (IAT) sensor uses a thermistor in order to control signal voltage to PCM. PCM supplies 5-volt reference and ground to sensor. When air is cold, resistance is high, and IAT signal voltage will be high. If intake air is warm, resistance is low, and IAT signal voltage will be low.

Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. IAT sensor measures temperature of air entering engine. PCM supplies 5 volts to IAT signal circuit. When IAT sensor is cold, sensor resistance is high. When air temperature increases, sensor resistance lowers. With high sensor resistance, PCM detects a high voltage on IAT signal circuit. With lower sensor resistance, PCM detects a lower voltage on IAT signal circuit. If PCM detects an excessively high IAT signal voltage, indicating a low temperature, this diagnostic trouble code (DTC) will set.

Intake Air Temperature (IAT) sensor uses a thermistor to control signal voltage to PCM. PCM supplies a 5-volt reference and ground to sensor. When air is cold, resistance is high, and IAT signal voltage will be high. If intake air is warm, resistance is low, and IAT signal voltage will be low.

Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures temperature of engine coolant. PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance lowers. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC will set.

Engine Coolant Temperature (ECT) sensor is a thermistor. ECT sensor has high resistance when cold and low resistance when hot. Powertrain Control Module (PCM) supplies 5 volts and ground to ECT sensor. ECT resistance is high (cold sensor) ECT signal voltage remains near 5 volts. As ECT sensor warms and resistance drops, signal circuit voltage is low. PCM and Alternate Fuel Engine Control Unit (AF ECU) monitor ECT signal circuit voltage to determine engine temperature.

Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures temperature of engine coolant. PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance lowers. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC will set.

Throttle Position (TP) sensor is a potentiometer. Powertrain Control Module (PCM) supplies 5 volts and ground to TP sensor. When throttle is depressed, TP signal voltage rises to near 5 volts. As throttle is released, TP signal voltage drops to around 0.6 volt. PCM and Alternate Fuel Engine Control Unit (AF ECU) monitor TP signal circuit voltage and determine angle (or opening) of throttle blade.

PCM provides TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of TP sensor rotor from closed throttle position to wide open throttle (WOT) position provides PCM with a signal voltage from less than one volt to more than 4 volts through TP sensor signal circuit. If PCM detects an excessively low signal voltage, this DTC will set.

PCM provides TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of TP sensor rotor from closed throttle position to Wide Open Throttle (WOT) position provides PCM with a signal voltage from less than one volt to more than 4 volts through TP sensor signal circuit. If PCM detects an excessively high signal voltage, DTC will set.

Engine Coolant Temperature (ECT) sensor monitors temperature of coolant. This input is used by PCM for engine control and as an enabling criteria for some diagnostics.

Airflow coming into engine is accumulated and used to determine if engine has been driven within conditions that would allow engine coolant to heat up normally to thermostat regulating temperature. If coolant temperature does not increase normally or does not reach regulating temperature of thermostat, diagnostics that use engine coolant temperature as enabling criteria may not run when expected.

This DTC will only run once per ignition cycle within enabling conditions.

This DTC will set when there has been excessive time to reach closed loop fuel control.

Engine Coolant Temperature (ECT) sensor is a thermistor. ECT sensor has high resistance when cold and low resistance when hot. Powertrain Control Module (PCM) supplies 5 volts and ground to ECT sensor. When ECT resistance is high (cold sensor), ECT signal voltage remains near 5 volts. As ECT sensor warms and resistance drops, signal circuit voltage is pulled low. PCM and Alternate Fuel Control Module (AF ECU) monitor ECT signal circuit voltage to determine engines temperature.

Engine Coolant Temperature (ECT) sensor monitors temperature of coolant. This input is used by PCM for engine control, and as an enabling criteria for some diagnostics.

Airflow coming into engine is accumulated and used to determine if engine has been driven within conditions that would allow engine coolant to heat up normally to thermostat regulating temperature. If coolant temperature does not increase normally, or does not reach regulating temperature of thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.

DTC will only run once per ignition cycle within enabling conditions.

If engine coolant fails to reach a preset target temperature before a calculated airflow is accumulated, DTC will set.

When vehicle is first started, engine operates in an open loop operation, ignoring oxygen sensor signal and calculating air/fuel ratio based on inputs from Engine Coolant Temperature (ECT), the Throttle Position (TP) and Manifold Absolute Pressure (MAP) sensors only. PCM will begin by using oxygen sensor signal for controlling fuel delivery (closed loop) when the following conditions are met

Engine has run a minimum amount of time based on ECT at engine start up.
Oxygen Sensor (O2S1) has a varying voltage output showing that it is hot enough to operate properly.
ECT has increased a minimum amount based on ECT at engine start up.

PCM supplies a voltage of about 450 millivolts between Oxygen Sensor (O2S1) high signal and low signal circuit. O2S1 varies voltage within a range of about 1000 millivolts if exhaust is rich, down through about 100 millivolts if exhaust is lean.

Sensor is like an open circuit and produces no voltage when less than 600°F (315°C). An open sensor circuit or a cold sensor causes open loop operation.

Oxygen Sensor (O2S) is used to determine oxygen content of exhaust. Oxygen content of exhaust indicates when engine is operating lean or rich. When engine is operating lean, exhaust will have more oxygen content. Once at operating temperature, O2S will produce a voltage in relation to oxygen content of exhaust. O2S requires an operating temperature of 600°F (360°C) to produce voltage. O2S will produce more voltage when exhaust is rich and less voltage when exhaust is lean. O2S operating voltage range is approximately 0.10 volt (100 mV) to one volt (1000 mV). Powertrain Control Module (PCM) supplies a reference voltage to O2S of approximately 450 mV.

PCM supplies a voltage of about 0.45 volt between Oxygen Sensor (O2S1) high signal and low signal circuit. O2S1 varies voltage within a range of about one volt if exhaust is rich, down through about 0.10 volt if exhaust is lean.

Sensor is like an open circuit and produces no voltage when less than 600°F (315°C). An open sensor signal circuit or a cold sensor causes open loop operation.

PCM continuously monitors Oxygen Sensor (O2S1) activity for 100 seconds. During monitoring period, PCM counts number of times O2S1 switches from rich to lean, and from lean to rich, then adds time O2S1 took to complete all switches. With this information, an average time for all switches can be determined. Whenever average time to switch is too slow, a DTC P0133 will set.

This DTC tests the Powertrain Control Module (PCM) and NOT the Alternative Fuels Engine Control Unit (AF ECU). PCM continuously monitors oxygen sensor 1 (O2S 1) activity for 100 seconds. During monitoring period, PCM counts the number of times O2S 1 switches rich to lean, and lean to rich, then adds time O2S 1 took to complete all switches. With this information, an average time for all switches can be determined.

PCM continuously monitors oxygen sensor (O2S1) activity for 100 seconds. During monitor period, PCM counts number of times that O2S1 switches from rich to lean and from lean to rich and adds amount of time that O2S1 took in order to complete all of switches. With this information, you can determine an average time for all of the switches. If average time to switch is too slow, a DTC P0133 will set.

Sensor is like an open circuit and produces no voltage when less than 600°F (315°C). An open sensor signal circuit or a cold sensor causes an open loop operation.

Oxygen Sensor (O2S) is used to determine oxygen content of exhaust. Oxygen content of exhaust indicates when engine is operating lean or rich. When engine is operating lean, exhaust will have more oxygen content. Once at operating temperature, O2S will produce a voltage in relation to the oxygen content of the exhaust. O2S requires an operating temperature of 600°F (360°C) to produce voltage. O2S will produce more voltage when exhaust is rich and less voltage when exhaust is lean. O2S operating voltage range is 0.1-1 volt (100-1000 mV).

Powertrain Control Module (PCM) supplies a reference voltage to O2S. This reference voltage is around 450 mV. Alternate Fuel Engine Control Unit (AF ECU) monitors reference voltage as well as voltage produced by O2S.

During normal closed loop fuel control operation, AF ECU will add fuel (enriches mixture) when O2S indicates a lean exhaust condition. When O2S indicates a rich exhaust content, AF ECU will subtract fuel (lean-out mixture). This oscillation above and below reference voltage (sometimes referred to as activity or switching) can be monitored using O2S signal voltage.

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

PCM has capability to monitor this process by using a rear heated oxygen sensor (HO2S2). HO2S2 , located in exhaust stream past catalytic converter, produces an output signal which indicates storage capacity of catalyst. This in turn indicates catalysts ability to convert exhaust emissions effectively. If catalyst is functioning properly, HO2S2 signal will be far less active than signal produced by front oxygen sensor (O2S1).

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

PCM has capability to monitor this process by using a rear heated oxygen sensor (HO2S2). HO2S2 , located in exhaust stream past catalytic converter, produces an output signal which indicates storage capacity of catalyst. This in turn indicates catalyst's ability to convert exhaust emissions effectively. If catalyst is functioning properly, HO2S2 signal will be far less active than signal produced by front oxygen sensor (O2S1).

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

PCM has capability to monitor this process by using a rear heated oxygen sensor (HO2S2). HO2S2, located in exhaust stream past catalytic converter, produces an output signal which indicates storage capacity of catalyst. This in turn indicates catalyst's ability to convert exhaust emissions effectively. If catalyst is functioning properly, HO2S2 signal will be far less active than signal produced by front oxygen sensor (O2S1).

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

PCM has capability to monitor this process by using a rear heated oxygen sensor (HO2S2). HO2S2, located in exhaust stream past catalytic converter, produces an output signal which indicates storage capacity of catalyst. This in turn indicates catalyst's ability to convert exhaust emissions effectively. If catalyst is functioning properly, HO2S2 signal will be far less active than signal produced by front oxygen sensor (O2S1).

PCM controls air/fuel metering system in order to provide best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during open and closed loop. During open loop, PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed loop, PCM adds oxygen sensor inputs to calculate short and long term fuel trim (fuel delivery adjustments). Short term fuel trim values change rapidly in response to HO2S voltage signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel (A/F) ratio of 14.7:1. Fuel Trim (FT) index is average of short and long term fuel trim and purge learn memory based on engine speed and load. If PCM detects an excessively lean condition, this DTC will set.

Exhaust Oxygen Sensor (O2S) is used to determine oxygen content of exhaust. Oxygen content indicates when engine is operating lean or rich. When engine is operating lean, exhaust will have more oxygen content. Once at operating temperature, O2S will produce a voltage in relation to oxygen content of exhaust. O2S requires an operating temperature of 600°F (360°C) to produce voltage. O2S will produce more voltage when exhaust is rich and less voltage when exhaust is lean. O2S operating voltage range is 0.10-1 volt (100-1000 mV).

Alternate Fuel Engine Control Module (AF ECU) uses closed loop air/fuel metering system when O2S is at operating temperature. During normal closed loop fuel control operation, AF ECU will add fuel (enriches mixture) when O2S indicates lean exhaust content. When O2S indicates rich exhaust content, AF ECU will subtract fuel (lean out mixture). This addition and subtraction to air/fuel mixture may be indicated on scan tool as long and short term fuel trim values. Short term values are adjustments to fuel mixture that occur quickly. Long term values are adjustments to fuel mixture that accumulate over longer periods of time. Long and short term fuel trim values are displayed on scan tool as percent. Positive percentage values indicate fuel is being added and negative percentage values indicate fuel is being subtracted from the mixture.

PCM controls air/fuel metering system in order to provide best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled during open and closed loop. During open loop, PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed loop, oxygen sensor inputs are added and used by PCM to calculate short and long term fuel trim (fuel delivery adjustments). Short term fuel trim values change rapidly in response to heated oxygen sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustments in order to maintain air/fuel ratio of 14.7:1. Fuel trim index is average of short and long term fuel trim and purge learn memory based on engine speed and load. Fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from Evaporative Emission (EVAP) canister is causing a rich condition. If PCM detects an excessively rich condition, this diagnostic trouble code (DTC) will set. If PCM detects excessive vapor then a pass is logged.

PCM enables appropriate fuel injector on intake stroke for each cylinder. An ignition voltage is supplied to fuel injectors. PCM controls each fuel injector by grounding control circuit via a solid state device called a driver. PCM monitors status of each driver. If PCM detects an incorrect voltage for commanded state of driver, a fuel injector control DTC sets.

Transmission fluid pump is constantly circulating fluid through torque converter. Hot fluid leaving converter flows through transmission cooler lines to oil cooler, located in vehicle radiator. From cooler, fluid returns to transmission.

Lube 1 fluid flows through input shaft to lubricate transmission components in front of transmission. Lube 2 fluid circuit is fed by line pressure at pressure regulator valve. Lube 2 fluid flows through oil feed pipes, and into forward clutch support. Lube 2 fluid provides lubrication to rear components of transmission.

When PCM detects a high transmission fluid temperature for a long period of time, then DTC P0218 sets.

PCM uses information from Ignition Control Module (ICM) and Camshaft Position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in crankshaft rotation speed for each cylinder, PCM is able to detect individual misfire events. A misfire rate that is high enough can cause 3-way catalytic (TWC) converter to overheat under certain conditions. Malfunction Indicator Lamp (MIL) will flash on and off when conditions for TWC converter overheating are present.

PCM uses information from Ignition Control Module (ICM) and Camshaft Position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in crankshaft rotation speed for each cylinder, PCM is able to detect individual misfire events. A misfire rate that is high enough can cause 3-way catalytic converter to overheat under certain conditions. Malfunction Indicator Lamp (MIL) will flash on and off when conditions for 3-way catalytic converter overheating are present.

PCM uses information from Ignition Control Module (ICM) and Camshaft Position (CMP) sensor in order to determine when an engine misfire occurs. By monitoring variations in crankshaft rotation speed for each cylinder, PCM is able to detect individual misfire events. A high misfire rate can cause the 3-way catalytic (TWC) converter to overheat under certain conditions. Malfunction Indicator Lamp (MIL) will flash on and off when conditions for TWC converter overheating are present.

PCM uses information from Ignition Control (ICM) module and Camshaft Position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in crankshaft rotation speed for each cylinder, PCM is able to detect individual misfire events. A misfire rate that is high enough can cause 3-way catalytic converter to overheat under certain conditions. Malfunction Indicator Lamp (MIL) will flash on and off when conditions for 3-way catalytic converter overheating are present.

Knock Sensor (KS) produces an AC voltage at all engine speeds and loads. PCM then adjusts spark timing based on amplitude and frequency of KS signal. PCM uses KS signal to calculate average voltage. Then PCM assigns a voltage value. PCM checks knock sensor and related wiring by comparing actual knock signal to assigned voltage range. A normal KS signal should stay outside assigned voltage range. This DTC will set if KS signal is within assigned voltage range or not present, or if PCM malfunctions in a manner that will not allow proper diagnosis of KS system.

Knock Sensor (KS) produces an AC voltage at all engine speeds and loads. PCM then adjusts spark timing based on amplitude and frequency of KS signal. PCM uses KS signal in order to calculate average voltage. Then PCM assigns a voltage value. PCM checks KS and related wiring by comparing actual knock signal to assigned voltage range. A normal KS signal should stay within assigned voltage range.

Crankshaft Position (CKP) sensor signal indicates crankshaft speed and position. CKP sensor is connected directly to PCM.

Crankshaft Position (CKP) sensor is connected to Ignition Control (IC) module. CKP sensor is mounted near crankshaft and monitors a toothed crankshaft reluctor wheel mounted to crankshaft. When crankshaft rotates, a signal is induced into CKP sensor. Based upon signal received from CKP sensor, IC module supplies a CKP signal on CKP 7X reference circuit. For each one engine revolution, IC module pulses CKP 7X reference circuit 7 times. Powertrain Control Module (PCM) and Alternate Fuel Engine Control Unit (AF ECU) use CKP 7X signal to determine engine speed, crankshaft position and cylinder misfire condition.

Crankshaft Position (CKP) sensor signal indicates crankshaft speed and position. CKP sensor is connected directly to Ignition Control Module (ICM).

Camshaft Position (CMP) sensor indicates camshaft position so PCM can determine which cylinder is misfiring when a misfire is present. With engine running, CMP activity counter will increment. Whenever PCM receives an intermittent signal from CMP, then CMP resync counter will increment.

Camshaft Position (CMP) sensor indicates camshaft position so PCM can determine which cylinder is misfiring when a misfire is present. Whenever PCM receives an intermittent signal from CMP, CMP resync counter will increment.

A 3-way catalytic (TWC) converter is used in order to control exhaust emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and oxides of nitrogen (NOx). The catalyst within converter promotes a chemical reaction which oxidizes HC and CO that is present in exhaust gas. This process will convert HC and CO into a harmless water vapor and CO2 and will reduce NOx, converting NOx into nitrogen. The catalytic converter also has ability to store oxygen. PCM has capability to monitor this process by using a Heated Oxygen Sensor (HO2S) which is in exhaust stream past 3-way catalytic converter. HO2S produces an output signal which indicates oxygen storage capacity of catalyst. This in turn indicates the catalyst's ability to convert the exhaust emissions effectively. PCM monitors catalyst efficiency by first allowing catalyst to heat, waiting for a stabilization period while engine is idling. Then, PCM adds and removes fuel while monitoring reaction of HO2S. When catalyst is functioning properly, HO2S2 response to extra fuel is slow compared to the O2S1. When HO2S2 response is close to that of O2S1, oxygen storage capability or efficiency of catalyst is considered to be bad and MIL will illuminate.

A 3-way catalytic converter is used in order to control exhaust emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and oxides of nitrogen (NOx). Catalyst within converter promotes a chemical reaction which oxidizes HC and CO present in exhaust gas. This converts HC and CO into harmless water vapor and carbon dioxide, and reduces NOx, converting NOx into nitrogen. Catalytic converter also has ability to store oxygen. PCM has capability to monitor this process by using a Heated Oxygen Sensor (HO2S) which is in the exhaust stream past 3-way catalytic converter. HO2S produces an output signal which indicates oxygen storage capacity of catalyst. This in turn indicates catalyst's ability to convert exhaust emissions effectively. PCM monitors catalyst efficiency by first allowing catalyst to heat up, waiting for a stabilization period while engine is idling. Then, PCM adds and removes fuel while monitoring reaction of HO2S. When catalyst is functioning properly, HO2S2 response to extra fuel is slow compared to O2S1. When HO2S2 response is close to that of O2S1, oxygen storage capability or efficiency of catalyst is considered to be deficient and MIL will illuminate.

EVAP large leak test applies vacuum to Evaporative Emission (EVAP) system and monitors vacuum decay. PCM monitors the Fuel Tank Pressure (FTP) sensor signal to determine vacuum decay rate. At an appropriate time, PCM turns EVAP canister purge valve on (open) and EVAP vent valve on (closed). This allows engine to draw a vacuum on EVAP system. At a calibrated time, or vacuum level, PCM turns purge valve off (closed), sealing system, and monitors FTP sensor input in order to determine EVAP system vacuum. If system is unable to achieve calibrated vacuum level, or vacuum level decreases too rapidly, DTC P0440 will set.

EVAP small leak test applies vacuum to Evaporative Emission (EVAP) system and monitors vacuum decay. PCM monitors Fuel Tank Pressure (FTP) sensor signal to determine vacuum decay rate. At an appropriate time, PCM turns EVAP canister purge valve on (open) and EVAP vent valve on (closed). This allows engine to draw a vacuum on EVAP system. At a calibrated time, or vacuum level, PCM turns purge valve off (closed), sealing system, and monitors FTP sensor input in order to determine EVAP system vacuum decay. If system detects a leak larger than a calibrated amount DTC P0442 will set.

A restricted or blocked Evaporative Emission (EVAP) vent path is detected by PCM commanding purge valve on (open) and vent valve on (closed) allowing a vacuum to be applied to EVAP system. Once a calibrated vacuum level has been reached, PCM commands purge valve off (closed) and vent valve off (open) while monitoring Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If vacuum does not decrease to near zero in. H2O in a calibrated time, DTC P0446 will set.

PCM monitors Fuel Tank Pressure (FTP) sensor signal to detect vacuum decay and excess vacuum during enhanced Evaporative Emission (EVAP) diagnostic. PCM supplies a 5-volt reference and ground to sensor. FTP sensor signal voltage increases as fuel tank pressure decreases (negative pressure or vacuum, high voltage). FTP sensor signal voltage decreases as fuel tank pressure increases (positive pressure, low voltage). When FTP sensor signal is less than a predetermined value, DTC P0452 will set.

Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced evaporative emission (EVAP) diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as the fuel tank pressure decreases (negative pressure or vacuum, high voltage). The FTP sensor signal voltage decreases as the fuel tank pressure increases (positive pressure, low voltage). When FTP sensor signal voltage is more than a predetermined value, DTC P0453 will set.

Fuel level sender changes resistance based on fuel level. PCM monitors signal circuit of fuel level sender in order to determine fuel level. When fuel tank is full, sender resistance is high and PCM senses a high signal voltage. When fuel tank is empty, sender resistance is low and PCM senses a low signal voltage. PCM uses signal circuit of fuel level sender in order to calculate total remaining fuel in tank. PCM sends fuel level percent via class 2 serial data circuit to instrument cluster in order to control fuel gauge. Fuel level information is also used for misfire and EVAP diagnostics.

Fuel level sensor changes resistance based on fuel level. PCM monitors signal circuit of fuel level sensor in order to determine fuel level. When fuel tank is full, sensor resistance is high and PCM senses a high signal voltage. When fuel tank is empty, sensor resistance is low and PCM senses a low signal voltage. PCM uses signal circuit of fuel level sensor in order to calculate total remaining fuel in tank. PCM sends fuel level volume via class 2 serial data circuit to instrument cluster in order to control fuel gauge. Fuel level information is also used for misfire and EVAP diagnostics.

Battery voltage is supplied to cooling fan relay from cooling fan fuse. PCM controls cooling fan relay by grounding cooling fan relay control circuit via an internal solid state device called a driver. Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage potential of control circuit should be low (near zero volts). When PCM is commanding control circuit to a component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, the DTC will set.

PCM will monitor control circuit for the following

Short to ground.
Short to voltage.
Open circuit.
Open relay coil.
Internally shorted or excessively low resistance relay coil.

When PCM detects any of specified conditions, DTC will set and affected driver will be disabled.

Battery voltage is supplied to cooling fan 1 relay from cool fan 1 fuse. PCM controls cooling fan 1 relay by grounding low speed cooling fan relay control circuit via an internal solid state device called a driver. Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage potential of control circuit should be low (near zero volts). When PCM is commanding control circuit to a component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC will set.

PCM will monitor control circuit for the following

Short to ground.
Short to voltage.
Open circuit.
Open relay coil.
An internally shorted or excessively low resistance relay coil.

When PCM detects any of specified conditions, DTC will set and affected driver will be disabled.

Battery voltage is supplied to cooling fan Series/Parallel (S/P) relay and cooling fan 3 relay from cool fan 2 fuse. PCM controls relays by grounding high speed cooling fan relay control circuit via an internal solid state device called a driver. Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage potential of control circuit should be low (near zero volts). When PCM is commanding control circuit to a component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC will set.

PCM will monitor control circuit for short to ground, short to voltage and open circuit.

When PCM detects any of above conditions, DTC will set and affected driver will be disabled.

Automatic Transmission Output (shaft) Speed Sensor (AT OSS) provides vehicle speed information to PCM. AT OSS is a permanent magnet generator mounted to the transmission case. AT OSS produces an AC voltage as transmission speed sensor rotor teeth pass through sensor's magnetic field. AC voltage level increases as speed of vehicle increases. PCM converts AC voltage into a digital signal. PCM uses the vehicle speed signal to determine shift timing, Torque Converter Clutch (TCC) apply, TCC release, and gear ratio calculations.

When PCM detects a low output speed and vehicle has a large engine speed in a drive gear, then DTC P0502 sets.

Vehicle speed information is provided to PCM by Vehicle Speed Sensor (VSS). VSS is a permanent magnet generator that is mounted in transaxle and produces a pulsing voltage whenever vehicle speed is over about 5 KM/H. AC voltage level and the number of pulses increases with vehicle speed. PCM converts pulsing voltage into MPH and then supplies necessary signal to instrument panel for speedometer, odometer operation and to cruise control module and multi-function alarm module operation.

Automatic Transmission Output (shaft) Speed Sensor (AT OSS) provides vehicle speed information to PCM. AT OSS is a permanent magnet generator mounted to transmission case. AT OSS produces an AC voltage as transmission speed sensor rotor teeth pass through sensor's magnetic field. AC voltage level increases as speed of vehicle increases. PCM converts AC voltage into a digital signal. PCM uses vehicle speed signal to determine shift timing, Torque Converter Clutch (TCC) apply, TCC release, and gear ratio calculations.

When PCM detects a loss of vehicle speed while vehicle is in motion, then DTC P0503 sets.

Idle Air Control (IAC) valve is located in throttle body. valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. IAC valve motor is a 2-phase bi-polar permanent magnet stepper motor that is capable of highly accurate rotation, or movement, every time polarity of a winding is changed. This change in polarity can be seen when observing a test light connected between ground or battery voltage and an IAC valve circuit while PCM is attempting to change engine RPM. Test light will flash on or off each time polarity is changed. PCM does not use a physical sensor to determine IAC pintle position, but uses a predicted number of counts, one count represents one change in polarity which equals one step of stepper motor. PCM counts steps it has commanded to determine IAC pintle position. PCM uses IAC valve to control engine idle speed. It does this by changing pintle position in idle air passage of throttle body. This varies airflow around throttle plate when throttle is closed. To determine desired position of IAC pintle at idle or during deceleration, PCM refers to following inputs

Engine RPM.
Battery voltage.
Air temperature.
Engine coolant temperature.
Throttle position sensor angle.
Engine load.
Vehicle speed.

When ignition key is turned off after an ignition cycle, PCM will first seat IAC pintle in air by-pass bore, and then retract it a predetermined amount of counts to allow proper amount of air to by-pass throttle plate for engine start-up. This procedure is known as an IAC Reset.

Idle Air Control (IAC) valve is located in throttle body. Valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. IAC valve motor is a 2-phase bi-polar permanent magnet stepper motor that is capable of highly accurate rotation, or movement, every time polarity of a winding is changed. This change in polarity can be seen when observing a test light connected between ground or battery voltage and an IAC valve circuit while PCM is attempting to change engine RPM. Test light will flash on or off each time polarity is changed. PCM does not use a physical sensor to determine IAC pintle position, but uses a predicted number of counts, one count represents one change in polarity which equals one step of stepper motor. PCM counts steps it has commanded to determine IAC pintle position. PCM uses IAC valve to control engine idle speed. It does this by changing pintle position in idle air passage of throttle body. This varies airflow around throttle plate when throttle is closed. To determine desired position of IAC pintle at idle or during deceleration, PCM refers to following inputs

Engine RPM.
Battery voltage.
Air temperature.
Engine coolant temperature.
Throttle position sensor angle.
Engine load.
Vehicle speed.

PCM checks system voltage to make sure voltage stays within proper range. Damage to components, and incorrect input can occur when voltage is out of range. PCM monitors system voltage over an extended length of time. If PCM detects an excessively low system voltage, DTC P0562 will set.

This diagnostic test applies to internal microprocessor integrity conditions within control module. This diagnostic test also addresses if control module is not programmed.

Alternate Fuel Engine Control Unit (AF ECU) contains data storage areas. AF ECU runs a test on stored data called check-sum. This DTC is used to indicate a failure has occurred within AF ECU.

PCM uses generator turn on signal circuit to control load of generator on engine. A high side driver in PCM applies a voltage to voltage regulator. This signals voltage regulator to turn field circuit on and off. When PCM turns on high side driver, voltage regulator turns on field circuit. When PCM turns off high side driver, voltage regulator turns off field circuit.

PCM monitors state of generator turn on signal circuit. PCM should detect a low generator turn on signal circuit voltage when key is on and engine is off, or when charging system malfunctions. With engine running, PCM should detect a high generator turn on signal circuit. PCM performs KEY ON and RUN tests to determine status of generator turn on signal circuit. During KEY ON test, if PCM detects a high generator turn on signal circuit voltage, DTC P0621 will set. DTC P0621 will also set if, during RUN test, PCM detects a low generator turn on signal circuit. When DTC sets, PCM will send a class 2 serial data message to IPC to illuminate charge indicator.

PCM uses generator field duty cycle signal circuit to monitor duty cycle of generator. Generator field duty cycle signal circuit connects to high side of field winding in generator. A pulse width modulated (PWM) high side driver in voltage regulator turns field winding on and off. PCM uses PWM signal input to determine generator load on engine. This allows PCM to adjust idle speed to compensate for high electrical loads.

PCM monitors state of generator field duty cycle signal circuit. When key is in RUN position and engine is off, PCM should detect a duty cycle near zero percent. However, when engine is running, duty cycle should be between 5 percent and 100 percent. PCM monitors PWM signal using a KEY ON test and a RUN test. During tests, if PCM detects an out of range PWM signal, DTC P0622 will set. When DTC sets, PCM will send a class 2 serial data message to IPC to illuminate charge indicator.

Transmission Range (TR) switch is part of park/neutral position and back-up light switch assembly and is mounted on transmission manual shaft. TR switch is a multi-signal switch. PCM supplies ignition voltage to TR switch on 4 signal circuits (A, B, C, and P). Each gear selector lever position grounds one or more of the signal circuits in a unique pattern. In order to determine gear range selected by driver, PCM compares voltage combination on signal circuits to a TR switch combination table stored in memory. (Схема №16)

When PCM detects an invalid combination of TR switch signals, then DTC P0705 sets.

Brake switch indicates brake pedal status to PCM. Normally-closed brake switch supplies ignition voltage to PCM. Applying brake pedal opens switch, interrupting voltage to PCM. Releasing brake pedal resumes voltage to PCM. When PCM senses zero volts at brake switch input, PCM de-energizes Torque Converter Clutch (TCC) solenoid valve.

When PCM detects an open brake switch (stuck ON) during accelerations, then DTC P0719 sets.

When PCM detects a closed brake switch (stuck OFF) during decelerations, then DTC P0724 sets.

PCM continuously monitors Oxygen Sensor (O2S1) activity for 100 seconds. During monitor period, PCM counts number of times O2S1 switches from rich to lean and from lean to rich. You can determine a total for all switches with this information. If number of switches is too low, DTC P1133 will set.

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

PCM has capability to monitor this process by using a rear-heated oxygen sensor (HO2S2). HO2S2, located in exhaust stream past catalytic converter, produces an output signal which indicates storage capacity of catalyst. This in turn indicates catalysts ability to convert exhaust emissions effectively. If catalyst is functioning properly, HO2S2 signal will be far less active than signal produced by front Oxygen Sensor (O2S1).

In order to control emissions, a 3-way catalytic (TWC) converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

The powertrain control module (PCM) has the capability to monitor this process by using a rear Heated Oxygen Sensor (HO2S2). The HO2S2, located in the exhaust stream past the TWC converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S2 signal will be far less active than the signal produced by the front Oxygen Sensor (O2S1).

PCM can identify if vehicle fuel system is capable of supplying adequate amounts of fuel during heavy acceleration. This condition is called a power enrichment mode of operation. If power enrichment is requested during a closed loop operation, PCM will provide more fuel to engine. Under these conditions, PCM should detect a rich condition. If PCM does not detect a rich exhaust at this time, DTC will set. A plugged fuel filter, or a restricted fuel line can prevent adequate amounts of fuel from being supplied during power enrichment mode.

Gas Mass Sensor (GMS) and Mixture Control Valve (MCV) are contained in one non-serviceable assembly. GMS monitors mass and flow of gaseous fuel entering engine and converts this information into a GMS ACTUAL GAS FLOW signal circuit frequency. Alternate Fuel Engine Control Module (AF ECU) commands fuel flow by supplying MCV with a frequency signal. DESIRED GAS FLOW signal circuit frequency varies from 1050 Hz (0.40 gm/s) at idle, to 5000 Hz (18 gm/s) at wide open throttle.

AF ECU converts ACTUAL GAS FLOW signal circuit frequency into a grams per second value. During low fuel flow rates (such as at engine idle) GMS sensor actual gas circuit will produce a low frequency signal of approximately 700 Hz (0.21 gm/s). During high fuel flow rates (such as at wide open throttle-road load) GMS sensor will produce a high frequency signal of approximately 2700 Hz (16.65 gm/s). AF ECU monitors and compares actual gas flow rate to a calculated gas flow rate. Calculated gas flow rate is based upon a calculated Mass Air Flow (MAF) rate.

Alternate Fuel Engine Control Unit (AF ECU) contains electronic devices called output driver modules. Output driver modules provide switchable outputs (control circuits) for operating solenoids, relays, telltales and other devices. Each output has an internal fault line that AF ECU can monitor for faulted circuit conditions.

Two types of outputs can be used. High side drivers supply voltage on control circuit and low side drivers supply ground on control circuit. Currently all monitored outputs are low side drivers. For fault line to detect a failure, state of control circuit must be opposite of expected state. If AF ECU is commanding an output ON, then zero volts should be monitored by fault line. If AF ECU is commanding an output OFF, then voltage should be monitored by fault line.

Monitored control circuits include Malfunction Indicator Lamp (MIL) control, NGO enable output control, high pressure and low pressure lock-off solenoid control.

In order to detect an engine misfire at higher engine speeds, PCM must know of any variation between crankshaft sensor pulses. Most variations are due to machining of crankshaft reluctor wheel, however, other sources of variation are also possible. A crankshaft position system variation learn procedure must be performed any time that you perform the following service procedures, regardless of whether DTC P1336 is set

PCM replacement.
Engine replacement.
Crankshaft replacement.
Crankshaft balancer replacement.
Crankshaft Position (CKP) sensor replacement.
Any engine repairs which disturbs crankshaft/harmonic balancer to crankshaft position sensor relationship.

PCM measures variations and then calculates compensation factors needed in order to enable PCM to accurately detect an engine misfire at all speeds and loads. A scan tool must be used to command PCM to learn these variations. If for any reason PCM is unable to learn these variations or if variations are out of an acceptable range, PCM will set a DTC P1336. A DTC P1336 will also set if PCM has not had crankshaft position system variation learn procedure performed due to replacement or a reprogramming.

Fuel Pressure Sensor (FPS) is a potentiometer. Alternate Fuel Engine Control Unit (AF ECU) supplies 5-volt reference voltage and ground circuit to FPS sensor. When fuel level/tank pressure is full, FPS signal voltage increases to 4.1 volts. As fuel level/tank pressure decreases to empty, FPS signal voltage drops to approximately 0.5 volt. AF ECU monitors FPS signal circuit voltage and Fuel Temperature Sensor (FTS) to determine amount of fuel in fuel tank.

Fuel Pressure Sensor (FPS) is a potentiometer. Alternate Fuel Engine Control Unit (AF ECU) supplies 5-volt reference voltage and ground circuit to FPS sensor. When fuel level/tank pressure is full, FPS signal voltage increases to 4.1 volts. As fuel level/tank pressure decreases to empty, FPS signal voltage decreases to approximately 0.5 volt. AF ECU monitors FPS signal circuit voltage and Fuel Temperature Sensor (FTS) to determine amount of fuel in fuel tank.

This DTC tests for undesired intake manifold vacuum flow to Evaporative Emission (EVAP) system. PCM seals EVAP system by commanding EVAP purge valve OFF (closed) and EVAP vent valve ON (closed). PCM monitors Fuel Tank Pressure (FTP) sensor to determine if a vacuum is being drawn on EVAP system. If vacuum in EVAP system is more than a calibrated value within a calibrated time, DTC P1441 will set.

Body Control Module (BCM) produces the theft deterrent fuel enable signal when ignition is on and the proper ignition code voltage value is detected. The Powertrain Control Module (PCM) monitors the fuel enable signal during crank. If the proper signal is present on the Class 2 Serial Data Circuit, the PCM enables fuel delivery in order to allow the engine to start. If the PCM determines that the fuel enable signal is not present or incorrect while the engine is running, DTC P1626 is set. The engine continues to start and run as long as DTC P1626 is stored.

Vehicle Theft Deterrent (VTD) system is incorporated within Body Control Module (BCM). If BCM has been replaced, password must be relearned. If PCM is replaced, replacement PCM should learn password within a few seconds after ignition is turned on. This is an information code indicating that PCM is ready to learn VTD password.

PCM controls fuel injector operation based on a Vehicle Theft Deterrent (VTD) password from vehicle Body Control Module (BCM). When ignition is first turned on, BCM sends a programmed theft deterrent password to PCM. PCM acknowledges password and responds to BCM that normal fuel injector operation will continue. When starting engine, PCM looks for a password from BCM through Class 2 serial data circuit. If password is not recognized or not present, PCM will disable engine. If an incorrect or no password is received, this indicates that engine will start and stall immediately. Security indicator will flash on Instrument Panel Cluster (IPC) for approximately 4 seconds. If an incorrect or disable password is received more than 3 times, this indicates that engine is disabled for at least 10 minutes and that Security indicator will illuminate continuously on IPC for approximately 3 seconds then flash on IPC for 10 minutes. If PCM loses communication with BCM within same ignition cycle, vehicle will enter fail-enable mode and continue to run on following ignition cycles.

Engine Controls Self-Diagnostics - 2.2L & 2.4L: Overview Oldsmobile Alero I

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