Crankshaft Position Sensor Description
This Electronic Ignition (EI) system uses a magnetic crankshaft position sensor. This sensor protrudes through its mount to within approximately 1.3 mm (0.05 in.) of the crankshaft reluctor. The reluctor is a special wheel attached to the crankshaft with the slots machined into it, which are equally spaced. The last slot is wider and serves to generate a sync pulse. As the crankshaft rotates, the slots in the reluctor change the magnetic field of the sensor, creating an induced voltage pulse. The longer pulse of the last slot identifies a specific orientation of the crankshaft and allows the Engine Control Module (ECM) to determine the crankshaft orientation at all times. The ECM uses this information to generate timed ignition and injection pulses that it sends to the ignition coils and to the fuel injectors.
Camshaft Position Sensor Description
The Camshaft Position (CMP) sensor sends a CMP signal to the Engine Control Module (ECM). The ECM uses this signal as a "sync pulse" to trigger the injectors in the proper sequence. The ECM uses the CMP signal to indicate the position of the #1 piston during its power stroke. This allows the ECM to calculate true sequential fuel injection mode of operation. If the ECM detects an incorrect CMP signal while the engine is running, DTC P0341 will set. If the CMP signal is lost while the engine is running, the fuel injection system will shift to a calculated sequential fuel injection mode based on the last fuel injection pulse, and the engine will continue to run. As long as the fault is present, the engine can be restarted.
Oxygen Sensors Description
The O2S sensor is located in the exhaust manifold. The HO2S is located in the exhaust pipe. The oxygen sensors indicate to the ECM the amount of oxygen in the exhaust gas, and the ECM changes the air/fuel ratio to the engine by controlling the fuel injectors.
The best air/fuel ratio to minimize exhaust emissions is 14.7: 1, which allows the catalytic converter to operate most efficiently. Because of the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a "Closed Loop" system.
The ECM uses voltage inputs from several sensors to determine how much fuel to provide to the engine. The fuel is delivered under one of several conditions, called "modes".
Engine Coolant Temperature Sensor Description
The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream.
The Engine Control Module (ECM) supplies 5 V to the ECT sensor through a resistor in the ECM and measures the change in voltage. The voltage will be high when the engine is cold and low when the engine is hot. By measuring the change in voltage, the ECM can determine the coolant temperature. The engine coolant temperature affects most of the systems that the ECM controls. A failure in the ECT sensor circuit should set a DTC P0117 or P0118. Remember, these DTC indicate a failure in the ECT circuit, so proper use of the chart will lead either to repairing a wiring problem or to replacing the sensor to repair a problem properly.
Throttle Position Sensor Description
The Throttle Position (TP) sensor is a potentiometer connected to the throttle shaft of the throttle body. The TP sensor electrical circuit consists of a 5 V supply line and a ground line, both provided by the Engine Control Module (ECM). The ECM calculates the throttle position by monitoring the voltage on this signal line. The TP sensor output changes as the accelerator pedal is moved, changing the throttle valve angle. At a closed throttle position, the output of the TP sensor is low, about 0.5 V. As the throttle valve opens, the output increases so that, at Wide Open Throttle (WOT), the output voltage will be about 5 V.
The ECM 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 injector and an unstable idle, because the ECM thinks the throttle is moving. A problem in any of the TP sensor circuits should set a DTC P0122 or P0123. Once the DTC is set, the ECM will substitute a default value for the TP sensor and some vehicle performance will return. A DTC P0121 will cause a high idle speed.
Catalyst Monitor Oxygen Sensors Description
3-way catalytic converters are used to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Nitrogen Oxide (NOx). The catalyst within the converters promotes a chemical reaction. This reaction oxidizes the HC and CO present in the exhaust gas and converts them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting it to nitrogen. The ECM can monitor this process using the O2 Bank 1 Sensor 1 and O2 Bank 1 Sensor 2 sensors. These sensors produce an output signal which indicates the amount of oxygen present in the exhaust gas entering and leaving the 3-way converter. This indicates the catalyst's ability to efficiently convert exhaust gasses. If the catalyst is operating efficiently, the O2 Bank 1 Sensor 1 sensor signals will be more active than the signals produced by the O2 Bank 1 Sensor 2 sensor. The catalyst monitor sensors operate the same way as the fuel control sensors. The sensor's main function is catalyst monitoring, but they also have a limited role in fuel control. If a sensor output indicates a voltage either above or below the 450 mV bias voltage for an extended period of time, the Engine Control Module (ECM) will make a slight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring.
A problem with the O2 Bank 1 Sensor 1 sensor circuit will set DTC P0131, P0132, P0133 or P0134 depending on the special condition. A problem with the O2 Bank 1 Sensor 2 sensor signal will set DTC P0137, P0138, P0140 or P0141 depending on the special condition.
A fault in the Heated Oxygen Sensor (HO2S), heater element or its ignition feed or ground will result in lower oxygen sensor response. This may cause incorrect catalyst monitor diagnostic results.
Intake Air Temperature Sensor Description
The Intake Air Temperature (IAT) sensor is a thermistor, a resistor which changes value based on the temperature of the air entering the engine.
The Engine Control Module (ECM) provides 5 V to the IAT sensor through a resistor in the ECM and measures the change in voltage to determine the IAT. The voltage will be high when the manifold air is cold and low when the air is hot. The ECM knows the intake IAT by measuring the voltage.
The IAT sensor is also used to control spark timing when the manifold air is cold.
A failure in the IAT sensor circuit sets a diagnostic trouble code P0112 or P0113.
Throttle Actuator Control (TAC) System Description
The Throttle Actuator Control (TAC) system is used to improve emissions, fuel economy, and driveability. The TAC system eliminates the mechanical link between the accelerator pedal and the throttle plate. The TAC system eliminates the need for a cruise control module and idle air control motor. The following is a list of TAC system components
- The accelerator pedal assembly includes the following components: The accelerator pedal. The Accelerator Pedal Position (APP) sensor. The APP sensor 2.
- The throttle body assembly includes the following components: The Throttle Position (TP) sensor 1. The TP sensor 2. The throttle actuator motor. The throttle plate.
- The Engine Control Module (ECM).
The ECM monitors the driver demand for acceleration with 2 APP sensors. The APP sensor 1 signal voltage range is from about 0.7 - 4.5 V as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The APP sensor 2 range is from about 0.3 - 2.2 V as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The ECM processes this information along with other sensor inputs to command the throttle plate to a certain position.
The throttle plate is controlled with a direct current motor called a throttle actuator control motor. The ECM can move this motor in the forward or reverse direction by controlling battery voltage and/or ground to 2 internal drivers. The throttle plate is held at a 5.7° TPS rest position using a constant force return spring. This spring holds the throttle plate to the rest position when there is no current flowing the actuator motor.
The ECM monitors the throttle plate angle with 2 TP sensors. The TP sensor 1 signal voltage range is from about 0.7 - 4.3 V as the throttle plate is moved from 0% to Wide Open Throttle (WOT). The TP sensor 2 voltage range is from about 4.3 - 0.7 V as the throttle plate is moved from 0% to WOT.
The ECM performs diagnostics that monitor the voltage levels of both APP sensors, both TP sensors, and the throttle actuator control motor circuit. It also monitors the spring return rate of both return springs that are housed internal to the throttle body assembly. These diagnostics are performed at different times based on whether the engine is running, or not running.
Every ignition cycle, The ECM performs a quick throttle return spring test to make sure the throttle plate can return to the 7% rest position from the 0% position. This is to ensure that the throttle plate can be brought to the rest position in case of an actuator motor circuit failure.
Manifold Absolute Pressure Sensor Description
The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from engine load and speed changes and converts these to a voltage output.
A closed throttle on engine coast down produces a relatively low MAP output. MAP is the opposite of vacuum. When manifold pressure is high, vacuum is low. The MAP sensor is also used to measure barometric pressure. This is performed as part of MAP sensor calculations. With the ignition ON and the engine not running, the Engine Control Module (ECM) will read the manifold pressure as barometric pressure and adjust the air/fuel ratio accordingly. This compensation for altitude allows the system to maintain driving performance while holding emissions low. The barometric function will update periodically during steady driving or under a wide open throttle condition. In the case of a fault in the barometric portion of the MAP sensor, the ECM will set to the default value.
A failure in the MAP sensor circuit sets a diagnostic trouble codes P0107, P0108 or P0106.
The following tables show the difference between absolute pressure and vacuum related to MAP sensor output, which appears as the top row of both tables.
Engine Control Module Description
The Engine Control Module (ECM), located inside the engine compartment, is the control center of the fuel injection system. It constantly looks at the information from various sensors and controls the systems that affect the vehicle's performance. The ECM also performs the diagnostic functions of the system. It can recognize operational problems, alert the driver through the Malfunction Indicator Lamp (MIL), and store diagnostic trouble code(s) which identify the problem areas to aid the technician in making repairs.
There are no serviceable parts in the ECM. The calibrations are stored in the ECM in the Programmable Read Only Memory (PROM).
The ECM supplies either 5 or 12 V to power the sensors or switches. This is done through resistances in the ECM which are so high in value that a test light will not come on when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because its resistance is too low. You must use a digital voltmeter with a 10 mohms input impedance to get accurate voltage readings. The ECM controls output circuits such as the fuel injectors, the Idle Air Control (IAC) valve, the A/C clutch relay, etc., by controlling the ground circuit through transistors or a device called a "quad-driver".
Knock Sensor Description
The knock sensor detects abnormal knocking in the engine. The sensor is mounted in the engine block near the cylinders. The sensor produces an AC output voltage which increases with the severity of the knock. This signal is sent to the Engine Control Module (ECM). The ECM then adjusts the ignition timing to reduce the spark knock.
Scheme 1
Scheme 2
- Remove the battery.
- Remove the ECM bracket nuts.
- Disconnect the ECM connector.
- Remove the ECM retaining nuts and the ECM.