Engine Control System - 4.8L, 5.3L, & 6.0L (Introduction): Overview Chevrolet SSR I

Engine Controls Schematic Icons

Engine Controls Schematic Icons Icon Icon Definition NOTE: The OBD II symbol is used on the circuit diagrams in order to alert the technician that the circuit is essential for proper OBD II emission control circuit operation. Any circuit which fails and causes the malfunction indicator lamp (MIL) to turn ON, or causes emissions-related component damage, is identified as an OBD II circuit. IMPORTANT: Twisted-pair wires provide an effective shield that helps protect sensitive electronic components from electrical interference. If the wires were covered with shielding, install new shielding. In order to prevent electrical interference from degrading the performance of the connected components, you must maintain the proper specification when making any repairs to the twisted-pair wires shown : The wires must be twisted a minimum of 9 turns per 31 cm (12 in) as measured anywhere along the length of the wires The outside diameter of the twisted wires must not exceed 6.0 mm (0.25 in)

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Malfunction Indicator Lamp (MIL) Operation

The malfunction indicator lamp (MIL) is located in the instrument panel cluster. The MIL will display as either SERVICE ENGINE SOON or one of the following symbols when commanded ON

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The MIL indicates that an emissions related fault has occurred and vehicle service is required.

The following is a list of the modes of operation for the MIL

1. The MIL illuminates when the ignition is turned ON, with the engine OFF. This is a bulb test to ensure the MIL is able to illuminate.
2. The MIL turns OFF after the engine is started if a diagnostic fault is not present.
3. The MIL remains illuminated after the engine is started if the control module detects a fault. A diagnostic trouble code (DTC) is stored any time the control module illuminates the MIL due to an emissions related fault. The MIL turns OFF after three consecutive ignition cycles in which a Test Passed has been reported for the diagnostic test that originally caused the MIL to illuminate.
4. The MIL flashes if the control module detects a misfire condition which could damage the catalytic converter.
5. When the MIL is illuminated and the engine stalls, the MIL will remain illuminated as long as the ignition is ON.
6. When the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition is cycled OFF and then ON.

Throttle Actuator Control (TAC) System Description

The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions

1. Accelerator pedal position (APP) sensing
2. Throttle positioning to meet driver and engine demands
3. Throttle position sensing
4. Internal diagnostics
5. Cruise control functions
6. Manage TAC electrical power consumption

The TAC system components include the following

1. The APP sensors
2. The throttle body assembly
3. The TAC module
4. The powertrain control module (PCM)

Fuel System Overview

The fuel tank stores the fuel supply. The electric fuel pump supplies fuel through an in-line fuel filter to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pressure regulator maintains the correct fuel pressure to the fuel injection system. A separate pipe returns unused fuel to the fuel tank.

Fuel Metering Modes of Operation

The powertrain control module (PCM) uses inputs from several sensors in order to determine how much fuel to supply to the engine. The fuel is delivered during one of several engine operating conditions called modes. The PCM controls all modes.

1. The Starting Mode - With the ignition switch in the ON position, before engaging the starter, the PCM energizes the fuel pump relay for 2 seconds allowing the fuel pump to build pressure. Speed density is determined by inputs from the engine RPM, the intake air temperature (IAT) and the manifold absolute pressure (MAP). The PCM first tests speed density, then switches to the mass air flow (MAF) sensor. The PCM also uses the engine coolant temperature (ECT), the throttle position (TP), and the manifold absolute pressure (MAP) sensors to determine the proper air/fuel ratio for starting. The PCM controls the amount of fuel delivered in the starting mode by changing the width of the fuel injector pulse.
2. The Clear Flood Mode - If the engine floods, clear the engine by pushing the accelerator pedal down to the floor and then crank the engine. When the throttle position (TP) sensor is at wide open throttle (WOT), the PCM reduces the injector pulse width in order to increase the air-to-fuel ratio. The PCM maintains this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the PCM returns to the starting mode.
3. The Run Mode - The run mode has 2 conditions. These conditions are called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The PCM ignores the signal from the heated oxygen sensor (HO2S) and calculates the air/fuel ratio based on inputs from the ECT, the MAF, the MAP, and the TP sensors. The system stays in Open Loop until the following conditions are met: Both HO2Ss have varying voltage output, showing that they are hot enough to operate properly. This depends upon the engine temperature. The ECT sensor is above a specified temperature. A specific amount of time has elapsed after starting the engine. Specific values for the above conditions exist for each different engine. These values are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the PCM calculates the air/fuel ratio, fuel injector ON time, based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.
4. Acceleration Mode - When the driver pushes on the accelerator pedal, the air flow into the cylinders increases rapidly, while fuel flow tends to lag behind. In order to prevent possible hesitation, the PCM increases the pulse width to the fuel injectors in order to provide extra fuel during acceleration. The PCM determines the amount of fuel required based upon the throttle position, the coolant temperature, the MAP, the MAF, and the engine speed.
5. Deceleration Mode - When the driver releases the accelerator pedal, the air flow into the engine is reduced. The PCM reads the corresponding changes in the TP, the MAP, and the MAF. The PCM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as during a long, closed-throttle coast-down. The fuel shuts OFF in order to protect the three-way catalyst (TWC).
6. Battery Voltage Correction Mode - When the battery voltage is low, the PCM compensates for the weak spark delivered by the ignition system in the following ways: Increasing the amount of fuel delivered Increasing the idle RPM Increasing the ignition dwell time
7. Fuel Cut-off Mode - The PCM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability: The ignition is OFF. This prevents engine run-on. The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring. The engine speed is too high, above red line. The vehicle speed is too high, above the rated tire speed. During an extended, high speed, closed-throttle coast-down - This reduces the emissions and increases the engine braking. During extended deceleration, in order to protect the catalytic converters

EVAP System Operation

The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid valve to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid valve ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid valve OFF, fresh air is drawn through the vent solenoid valve and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid valve into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.

Electronic Ignition (EI) System Description

The electronic ignition (EI) system is responsible for producing and controlling a high energy secondary spark. This spark is used to ignite the compressed air/fuel mixture at precisely the correct time. This provides optimal performance, fuel economy, and control of exhaust emissions. This ignition system consists of a separate ignition coil connected to each spark plug by a short secondary wire. The driver modules within each coil assembly are commanded ON/OFF by the powertrain control module (PCM). The PCM primarily uses engine speed and position information from the crankshaft and camshaft position (CMP) sensors to control the sequence, dwell, and timing of the spark. The EI system consists of the following components

Modes of Operation

There is one normal mode of operation, with the spark under PCM control. If the CKP pulses are lost the engine will not run. The loss of a CMP signal may result in a longer crank time since the PCM cannot determine which stroke the pistons are on. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.

Sensor Description

This knock sensor (KS) system uses one or 2 broadband one-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration, or noise, level. The amplitude and frequency are dependant upon the level of knock that the KS detects. The control module receives the KS signal through a signal circuit. The KS ground is supplied by the engine block through the sensor housing.

One way the control module monitors the system is by output of a bias voltage on the KS signal wire. The bias voltage creates a voltage drop that the control module monitors and uses to help diagnose KS faults. The KS noise signal rides along this bias voltage, and due to the constantly fluctuating frequency and amplitude of the signal, will always be outside of the bias voltage parameters.

Another way the control module monitors the system is by learning the average normal noise output from the KS. The control module learns a minimum noise level, or background noise, at idle from the KS and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. The control module uses this noise channel, and the KS signal that rides along the noise channel, in much the same way as the bias voltage type does. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal KS signal.

In order to determine which cylinders are knocking, the control module only uses KS signal information when each cylinder is near top dead center (TDC) of the firing stroke. If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal KS signal will fall within the noise channel or will not be present. KS diagnostics are calibrated to detect faults with the KS circuitry inside the control module, the KS wiring, or the KS voltage output.

Air Intake System Description

The primary function of the air intake system is to provide filtered air to the engine. The system uses a cleaner element mounted in a housing. The cleaner housing is remotely mounted and uses intake ducts to route the incoming air into the throttle body. The secondary function of the air intake system is to muffle air induction noise. This is achieved through the use of resonators attached to the air intake ducts. The resonators are tuned to the specific powertrain. The mass air flow (MAF) sensor is attached to the outlet of the air cleaner housing. The air cleaner life indicator is located on an intake duct between the air cleaner housing and the throttle plate.