Part 2 of 2

CCD BUS
Various controllers and modules exchange information through a two-wire communication port called the CCD Bus. The PCM transmits various monitored input information and control requests to other modules on the CCD Bus. The PCM also receives information and requests that effects the control of its outputs from other controllers over the CCD Bus. The CCD Bus has a measurable voltage of approximately 2.5 volts.

Various modules exchange information through a communications port called the CCD Bus. 'The Powertrain Control Module (PCM) transmits the Malfunction Indicator Lamp (Check Engine) ON/OFF signal and engine RPM on the CCD Bus. The PCM receives the Air Conditioning select input, transaxle gear position input and speed control engage inputs over the CCD Bus. The PCM also receives the air conditioning evaporator temperature signal from the CCD Bus.

The following components access or send information on the CCD Bus.
- Instrument Panel
- Body Control Module
- Air Bag System Diagnostic Module
- Full ATC Display Head
- ABS Module
- Transmission Control Module
- Powertrain Control Module
- Travel Module (if equipped)

SYSTEM DIAGNOSIS
The PCM can test many of its own input and output circuits. If the PCM senses a fault in a major system, the PCM stores a Diagnostic Trouble Code (DTC) in memory.

For DTC information see On-Board Diagnostics.

TORQUE MANAGEMENT
The PCM receives the torque management input from the transmission control module. The PCM receives the input when the transmission shifts gears. In response, the PCM shuts off a number of fuel injectors when the transmission shifts gears.

FUEL INJECTOR

Fig. 4 Fuel Injector:

Fig. 5 Fuel Injector Location - Typical:

The fuel injectors are electrical solenoids. The injectors are positioned in the cylinder heads with the nozzle ends directly above the intake valve port. Fuel injectors are not interchangeable between engines.

The injector contains a pintle that closes OFF an orifice at the nozzle end. When electric current is supplied to the injector, the armature and needle move a short distance against a spring, allowing fuel to flow out the orifice. Because the fuel is under high pressure, a fine spray is developed in the shape of 2 streams. The spraying action atomizes the fuel, adding it to the air entering the combustion chamber.

IDLE AIR CONTROL MOTOR

Fig. 6 Idle Air Control Motor:

The idle air control motor attaches to the throttle body. It is an electric stepper motor.

The PCM adjusts engine idle speed through the idle air control motor to compensate for engine load, coolant temperature or barometric pressure changes.

The throttle body has an air bypass passage that provides air for the engine during closed throttle idle. The idle air control motor pintle protrudes into the air bypass passage and regulates air flow through it.

The PCM adjusts engine idle speed by moving the IAC motor pintle in and out of the bypass passage. The adjustments are based on inputs the PCM receives. The inputs are from the throttle position sensor, crankshaft position sensor, coolant temperature sensor, MAP sensor, vehicle speed sensor and various switch operations (brake, park/neutral, air conditioning).

When engine rpm is above idle speed, the IAC is used for the following functions:
- Off-idle dashpot
- Deceleration air flow control
- A/C compressor load control (also opens the passage slightly before the compressor is engaged so that the engine rpm does not dip down when the compressor engages)

Target Idle
Target idle is determined by the following inputs:
- Gear position
- ECT Sensor
- Battery voltage
- Ambient/Battery Temperature Sensor
- VSS
- TPS
- MAP Sensor

INTAKE AIR TEMPERATURE/MANIFOLD ABSOLUTE PRESSURE SENSOR - PCM INPUT

Fig. 7 Intake Air Temperature Sensor And MAP Sensor:

The MAP sensor mounts to the driver side of the intake manifold plenum. The IAT sensor and Manifold Absolute Pressure (MAP) sensor are a combined sensor.

The MAP serves as a PCM input, using a silicon based sensing unit, to provide data on the manifold vacuum that draws the air/fuel mixture into the combustion chamber. The PCM requires this information to determine injector pulse width and spark advance. When MAP equals Barometric pressure, the pulse width will be at maximum.

A 5 volt reference is supplied from the PCM and returns a voltage signal to the PCM that reflects manifold pressure. The zero pressure reading is 0.5 V and full scale is 4.5 V For a pressure swing of 0 - 15 psi the voltage changes 4.0 V. The sensor is supplied a regulated 4.8 - 5.1 volts to operate the sensor. Ground is provided through the sensor return circuit.

The MAP sensor input is the number one contributor to pulse width. The most important function of the MAP sensor is to determine barometric pressure. The PCM needs to know if the vehicle is at sea level or is it in Denver at 5000 feet above sea level, because the air density changes with altitude. It will also help to correct for varying weather conditions. If a hurricane was coming through the pressure would be very low or there could be a real fair weather, high pressure area. This is important because as air pressure changes the barometric pressure changes. Barometric pressure and altitude have a direct inverse correlation, as altitude goes up barometric goes down. The first thing that happens as the key is rolled ON, before reaching the crank position, the PCM powers up, comes around and looks at the MAP voltage, and based upon the voltage it sees, it knows the current barometric pressure relative to altitude. Once the engine starts, the PCM looks at the voltage again, continuously every 12 milliseconds, and compares the current voltage to what it was at key ON. The difference between current and what it was at key ON is manifold vacuum.

During key ON (engine not running) the sensor reads (updates) barometric pressure. A normal range can be obtained by monitoring known good sensor in you work area.

As the altitude increases the air becomes thinner (less oxygen). If a vehicle is started and driven to a very different altitude than where it was at key On the barometric pressure needs to be updated. Any time the PCM sees Wide Open throttle, based upon TPS angle and RPM it will update barometric pressure in the MAP memory cell. With periodic updates, the PCM can make its calculations more effectively.

The PCM uses the MAP sensor to aid in calculating the following:
- Manifold pressure
- Injector pulse-width
- Spark-advance programs
- Idle speed
- Decel fuel shutoff

The MAP sensor signal is provided from a single piezo resistive element located in the center of a diaphragm. The element and diaphragm are both made of silicone. As the pressures changes the diaphragm moves causing the element to deflect which stresses the silicone. When silicone is exposed to stress its resistance changes. As manifold vacuum increases, the MAP sensor input voltage decreases proportionally. The sensor also contains electronics that condition the signal and provide temperature compensation.

The PCM recognizes a decrease in manifold pressure by monitoring a decrease in voltage from the reading stored in the barometric pressure memory cell. The MAP sensor is a linear sensor; as pressure changes, voltage changes proportionately. The range of voltage output from the sensor is usually between 4.6 volts at sea level to as low as 0.3 volts at 26 in. Hg. Barometric pressure is the pressure exerted by the atmosphere upon an object. At sea level on a standard day, no storm, barometric pressure is 29.92 in. Hg. For every 100 feet of altitude, barometric pressure drops 0.10 in. Hg. If a storm goes through, it can either add (high pressure) or decrease (low pressure) from what should be present for that altitude. You should make a habit of knowing what the average pressure and corresponding barometric pressure is for your area. Always use the Diagnostic Test Procedures for MAP sensor testing.

The Intake Air Temperature (IAT) sensor measures the temperature of the intake air as it enters the engine. The sensor supplies one of the inputs the PCM uses to determine injector pulse width and spark advance.

MANIFOLD TUNING VALVE (MTV)

Fig. 8 Manifold Tuning Valve:

The valve opens a crossover passage in that connects both sides of the intake manifold plenum. It is an rotary solenoid.

The PCM controls the MTV solenoid. The manifold tuning valve optimizes acoustical tuning of the intake system during wide open throttle operation throughout the RPM range.

O2 SENSOR

Fig. 11 Headed Oxygen Sensor 1/1:

Fig. 12 Heated Oxygen Sensor 2/1:

The upstream oxygen sensor threads into the outlet flange of the exhaust manifold or.

Fig.13 Heated Oxygen Sensor 1/2, 2/2:

The downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic convertor.

The O2 Sensors are zirconium dioxide, four wire and heated. The heater uses two of the sensors' four wires. One is common ground, the other provides battery voltage to the heater from the ASD Relay. One of the remaining wires is a sensor signal input to the PCM. The fourth wire is signal ground. The O2 Sensors deliver a voltage signal (0 - 1 volt) to the PCM inversely proportional to the amount of oxygen in the exhaust. If the oxygen content is low, the output voltage is high; if the oxygen content is high, the output voltage low. The O2 Sensors must have a source of oxygen from outside the exhaust stream for comparison. O2 Sensors receive their fresh oxygen supply through the wire harness. This is why it is important to never solder an O2 Sensor connector or pack the connector with grease.

The Automatic Shutdown (ASD) relay supplies battery voltage to both the upstream and downstream heated oxygen sensors. The oxygen sensors are equipped with a heating element. The heating elements reduce the time required for the sensors to reach operating temperature. The O2 Sensor uses a Positive Thermal Coefficient (PTC) heater element. As temperature increases, resistance increases. At ambient temperatures around 21 °C (70 °F), the resistance of the heating element is approximately 6 ohms for the Downstream Sensor and is approximately 4.5 ohms for the Upstream Sensor. As the sensor's temperature increases, resistance in the heater element increases,

Upstream Oxygen Sensor 1/1
The input from the upstream heated oxygen sensor tells the PCM the oxygen content of the exhaust gas. Based on this input, the PCM fine tunes the air-fuel ratio by adjusting injector pulse width. Separate controlled ground circuits are run through the PCM for the upstream O2 sensors.

The sensor input switches from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean air-fuel mixture), the sensor produces voltage as low as 0.1 volt. When there is a lesser amount of oxygen present (rich air- fuel mixture) the sensor produces a voltage as high as 1.0 volt. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch.

The oxygen sensors are equipped with a heating element that keeps the sensors at proper operating temperature during all operating modes. Heating the sensor allows the system to enter into closed loop operation sooner. Also, it allows the system to remain in closed loop operation during periods of extended idle.

In Closed Loop operation the PCM monitors the O2S input (along with other inputs) and adjusts the injector pulse width accordingly. During Open Loop operation the PCM ignores the O2 sensor input. The PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.

Downstream Oxygen Sensor 1/2
The downstream heated oxygen sensor input is used to detect catalytic convertor deterioration. As the convertor deteriorates, the input from the downstream sensor begins to match the upstream sensor input except for a slight time delay. By comparing the downstream heated oxygen sensor input to the input from the upstream sensor, the PCM calculates catalytic convertor efficiency. If the oxygen leaving the catalyst is too lean (excess oxygen), the PCM increases the upstream O2 goal, which increases fuel in the mixture, causing less oxygen to be left over. Conversely, if the oxygen content leaving the catalyst is too rich (not enough oxygen) the PCM decreases the upstream O2 goal down which removes fuel from the mixture causing more oxygen to be left over. This function only occurs during downstream closed loop mode operation.

[1][2]SHORT RUNNER VALVE ([1][2]SRV)

Fig. 18 Short Runner Valve (SRV):

It is a manifold tuning system consisting of a solenoid, vacuum actuator, and intake runner butterfly valve integrated within intake manifold. Vacuum is supplied from the speed control vacuum reservoir.

The [1][2]SRV system operates under WOT conditions above 5000 rpm to maximize engine performance. When actuated by the PCM, the SRV solenoid energizes, allowing mechanical linkage to redirect the intake air flow to six short runners. The PCM looks for a current spike when actuating the solenoid. If the spike is not present, the PCM sets the DTC.

THROTTLE BODY

Fig. 21 Throttle Body:

The throttle body is located on the intake manifold. Fuel does not enter the intake manifold through the throttle body. Fuel is sprayed into the manifold by the fuel injectors.

Filtered air from the air cleaner enters the intake manifold through the throttle body. The throttle body contains an air control passage controlled by an Idle Air Control (IAC) motor. The air control passage is used to supply air for idle conditions. A throttle valve (plate) is used to supply air for above idle conditions.

Certain sensors are attached to the throttle body. The accelerator pedal cable, speed control cable and transmission control cable (when equipped) are connected to the throttle body linkage arm.

A (factory adjusted) set screw is used to mechanically limit the position of the throttle body throttle plate. Never attempt to adjust the engine idle speed using this screw. All idle speed functions are controlled by the PCM.

THROTTLE POSITION SENSOR (TPS)

Fig. 23 Throttle Position Sensor:

The throttle position sensor mounts to the side of the throttle body. The sensor connects to the throttle blade shaft. The TPS is a variable resistor that provides the Powertrain Control Module (PCM) with an input signal (voltage).

The signal represents throttle blade position. As the position of the throttle blade changes, the resistance of the TPS changes.

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the powertrain control module) represents throttle blade position. The TPS output voltage to the PCM varies from approximately 0.6 volt at minimum throttle opening (idle) to a maximum of 4.5 volts at wide open throttle.

Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. The PCM also adjusts fuel injector pulse width and ignition timing based on these inputs.

VACUUM RESERVOIR
The vacuum reservoir is located in the engine compartment. It is made of plastic.

The reservoir stores engine vacuum. Manifold vacuum is supplied from the brake booster check valve. The speed control vacuum supply hose has a check valve at the source (brake booster) to maintain the highest available vacuum level in the servo, reservoir and vacuum hoses. When engine vacuum drops, as in climbing a grade while driving, the reservoir supplies the vacuum needed to maintain proper speed control operation. The vacuum reservoir cannot be repaired and must be replaced if faulty.

CRANKSHAFT POSITION SENSOR

Fig. 26 Crankshaft Position Sensor Location:

The crankshaft sensor is located on the passengers side of the transmission housing, above the differential housing. The bottom of the sensor is positioned next to the drive plate.

The sensor is a hall effect device combined with an internal magnet. It is also sensitive to steel within a certain distance from it.

Engine speed and crankshaft position are provided through the crankshaft position sensor. The sensor generates pulses that are the input sent to the powertrain control module (PCM). The PCM interprets the sensor input to determine the crankshaft position. The PCM uses crankshaft position reference to determine injector sequence and ignition timing. Once the PCM determines crankshaft position, it begins energizing the injectors and coils in sequence.

Fig. 27 Timing Slots:

The crankshaft position sensor detects slots cut into the transmission driveplate extension. There are 3 sets of slots. Two sets contain 4 slots and one set contains 5 slots, for a total of 13 slots. Basic timing is set by the position of the last slot. Once the Powertrain Control Module (PCM) senses the last slot, it determines which piston will be next at TDC from the camshaft position sensor input. It may take the PCM one engine revolution to determine crankshaft position.

The PCM uses the Crankshaft Position sensor to calculate the following:
- Engine rpm
- TDC number 1 and 4
- Ignition coil synchronization
- Injector synchronization
- Camshaft-to-crankshaft misalignment (Timing belt skipped 1 tooth or more diagnostic trouble code)