Engine Controls - Theory & Operation Dodge Grand Caravan IV

INTRODUCTION

This article covers basic description and operation of engine performance related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.

Note. References to California models apply to California emission vehicles, which may be verified by underhood Vehicle Emission Control Label. California emissions may be available in other states.

Note. All models have a Vehicle Emission Control Information (VECI) Label. Chrysler permanently attaches the label in the engine compartment. It cannot be removed without defacing information and destroying the label. The label contains the vehicle's emission specifications and vacuum hose routings. All hoses must be connected and routed according to the label.

POWERTRAIN CONTROL MODULE

The Powertrain Control Module (PCM) is located on left side of engine compartment, near the front of the battery. (Scheme 1) The PCM is a digital computer containing a microprocessor. The PCM receives input signals from various switches and sensors referred to as PCM inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices referred to as PCM outputs.

Based on inputs the PCM receives, the PCM adjusts fuel injector pulse width, idle speed, ignition timing and canister purge operation. The PCM regulates the cooling fans, A/C and speed control systems. The PCM changes generator charge rate by adjusting the generator field.

The following inputs may be used by the PCM.

1. Air Conditioning Pressure Transducer
2. Ambient temperature Sensor
3. ASD Relay
4. Battery Temperature Sensor (NGC)
5. Battery Voltage
6. Brake Switch
7. Camshaft Position Sensor
8. Crankshaft Position Sensor
9. Distance Sensor (From Transmission Control Module)
10. EGR Position Feedback
11. Engine Coolant Temperature Sensor
12. Heated Oxygen Sensors
13. Ignition Sense
14. Intake Air Temperature Sensor
15. Knock Sensor
16. Leak Detection Pump Feedback
17. Manifold Absolute Pressure (MAP) Sensor
18. Park/Neutral
19. PCI Bus
20. Power Steering Pressure Switch
21. Proportional Purge Sense
22. Speed Control
23. Throttle Position Sensor
24. Torque Management Input
25. Transaxle Control Module (3.3/3.8L Only)
26. Transmission Control Relay (Switched B+) (2.4L Only)
27. Transmission Pressure Switches (2.4L Only)
28. Transmission Temperature Sensor (2.4L Only)
29. Transmission Input Shaft Speed Sensor (2.4L Only)
30. Transmission Output Shaft Speed Sensor (2.4L Only)
31. Transaxle Gear Engagement
32. Vehicle Speed

The following outputs may be used by the PCM.

1. Air Conditioning Clutch Relay
2. Automatic Shutdown (ASD) & Fuel Pump Relays
3. Data Link Connector (PCI & SCI Transmit)
4. Double Start Override
5. EGR Solenoid
6. Fuel Injectors
7. Generator Field
8. High Speed Fan Relay
9. Idle Air Control Motor
10. Ignition Coils
11. Leak Detection Pump
12. Low Speed Fan Relay
13. MTV Actuator
14. Proportional Purge Solenoid
15. SRV Valve
16. Speed Control Relay
17. Speed Control Vent Relay
18. Speed Control Vacuum Relay
19. Eight-Volt Output
20. Five-Volt Output
21. Torque Reduction Request
22. Transmission Control Relay (2.4L Only)
23. Transmission Solenoids (2.4L Only)
24. Vehicle Speed

The PCM adjusts injector pulse width (air/fuel ratio) based on the following inputs.

1. Battery Voltage
2. Intake Air Temperature Sensor
3. Engine Coolant Temperature
4. Engine Speed (Crankshaft Position Sensor)
5. Exhaust Gas Oxygen Content (Heated Oxygen Sensors)
6. Manifold Absolute Pressure
7. Throttle Position

The PCM adjusts engine idle speed through the idle air control motor based on the following inputs.

1. Brake Switch
2. Engine Coolant Temperature
3. Engine Speed (Crankshaft Position Sensor)
4. Park/Neutral (Transmission Gear Selection)
5. Transaxle Gear Engagement
6. Throttle Position
7. Vehicle Speed (From Transmission Control Module)

The PCM adjusts ignition timing based on the following inputs.

1. Intake Air Temperature
2. Engine Coolant Temperature
3. Engine Speed (Crankshaft Position Sensor)
4. Knock Sensor
5. Manifold Absolute Pressure
6. Park/Neutral (Transmission Gear Selection)
7. Transaxle Gear Engagement
8. Throttle Position

The Automatic Shutdown (ASD) and fuel pump relays are mounted externally, but are turned on and off by the PCM through the same circuit. The camshaft and crankshaft signals are sent to the PCM. If the PCM does not receive both signals within approximately one second of engine cranking, it deactivates the ASD and fuel pump relays. When these relays are deactivated, power is shutoff to the fuel injectors, ignition coils, fuel pump and the heating element in each oxygen sensor. The PCM contains a voltage converter that changes battery voltage to a regulated 8.0 volts. The 8.0 volts powers the camshaft position sensor, crankshaft position sensor and vehicle speed sensor. The PCM also provides a 5.0 volt supply for the engine coolant temperature sensor, intake air temperature sensor, manifold absolute pressure sensor and throttle position sensor.

The PCM contains a self-diagnostic system which stores a Diagnostic Trouble Code (DTC) if an electronic control system failure exists DTC may be retrieved from PCM for system diagnosis by using a scan tool. See SELF-DIAGNOSTIC SYSTEM .

Scheme 1

Clutch Volume Index

An important function of the PCM is to monitor Clutch Volume Index (CVI), CVIs represent the volume of fluid needed to compress a clutch pack.

The PCM monitors gear ratio changes by monitoring the Input and Output Speed Sensors. The Input, or Turbine Speed Sensor sends an electrical signal to the PCM that represents input shaft RPM. The Output Speed Sensor provides the PCM with output shaft speed information.

By comparing the two inputs, the PCM can determine transaxle gear position. This is important to the CVI calculation because the PCM determines CVIs by monitoring how long it takes for a gear change to occur. (Scheme 2)

Gear ratios can be determined by using the DRBIII(R) Scan Tool and reading the Input/Output Speed Sensor values in the "Monitors" display. Gear ratio can be obtained by dividing the Input Speed Sensor value by the Output Speed Sensor value.

For example, if the input shaft is rotating at 1000 RPM and the output shaft is rotating at 500 RPM, then the PCM can determine that the gear ratio is 2:1. In direct drive (3rd gear), the gear ratio changes to 1:1. The gear ratio changes as clutches are applied and released. By monitoring the length of time it takes for the gear ratio to change following a shift request, the PCM can determine the volume of fluid used to apply or release a friction element.

The volume of transmission fluid needed to apply the friction elements are continuously updated for adaptive controls. As friction material wears, the volume of fluid need to apply the element increases.

Certain mechanical problems within the input clutch assembly (broken return springs, out of position snap rings, excessive clutch pack clearance, improper assembly, etc.) can cause inadequate or out-of-range element volumes. Also, defective Input/Output Speed Sensors and wiring can cause these conditions. The following illustration identifies the appropriate clutch volumes and when they are monitored/updated. (Scheme 3)

Scheme 2

Scheme 3

Shift Schedules

The PCM has programming that allows it to select a variety of shift schedules. Shift schedule selection is dependent on the following

1. Shift Lever Position
2. Throttle Position
3. Engine Load
4. Fluid Temperature
5. Software Level

As driving conditions change, the PCM appropriately adjusts the shift schedule. Refer to the following illustration to determine the appropriate operation expected, depending on driving conditions. (Scheme 4)

Scheme 4

INPUT DEVICES

Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES , which control or produce voltage signals monitored by the PCM. The second category covers OUTPUT SIGNALS , which are components controlled by the PCM.

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device usage on a specific model, see WIRING DIAGRAMS . The available input signals include the following

A/C Pressure Transducer

A/C pressure transducer may also be referred to as A/C pressure sensor. The A/C pressure transducer is a switch that is installed on a fitting located on the refrigerant liquid line between the filter-drier and the expansion valve in the right rear corner of the engine compartment. (Scheme 5) An internally threaded hex fitting on the transducer connects it to the externally threaded Schrader-type fitting on the liquid line. A rubber "O" ring seals the connection between the transducer and the liquid line fitting. Three terminals within a molded plastic connector receptacle on the top of the transducer connects it to the vehicle electrical system through a take out and connector of the headlight and dash wiring harness. The A/C pressure transducer cannot be adjusted or repaired. If faulty or damaged, the transducer must be replaced.

The A/C pressure transducer monitors the pressures in the high side of the refrigerant system. The transducer will change its internal resistance in response to the pressures it monitors. The PCM provides a 5-volt reference signal and a sensor ground to the transducer, then monitors the output voltage of the transducer on a sensor return circuit to determine refrigerant pressure. The PCM is programmed to respond to this and other sensor inputs by controlling the operation of the A/C compressor clutch and the radiator cooling fan to help optimize A/C system performance, and to protect the system components from damage. The A/C pressure transducer input to the PCM will also prevent the A/C compressor clutch from engaging when ambient temperatures are below 50°F (10°C) due to the pressure/temperature relationship of the refrigerant. The Schrader-type valve in the liquid line fitting permits the A/C pressure transducer to be removed or installed without disturbing the refrigerant in the system.

Scheme 5

Auto Shutdown Relay

See AUTO SHUTDOWN RELAY under RELAYS under MISCELLANEOUS CONTROLS.

Battery Voltage

Powertrain Control Module (PCM) monitors battery voltage to determine fuel injector pulse width and generator field control. If battery voltage is not within specified range, PCM will increase fuel injector pulse width.

Brake Switch

Note. The brake switch may also be referred to as brakelight switch.

The brake switch is located under the instrument panel, at the brake pedal arm. (Scheme 6) The brake switch has 3 internal switches controlling various functions of the vehicle. Its main function is to control operation of the vehicle's brake lights. Other functions include speed control deactivation, brake sense for the anti-lock brake system and brake sense for the brake transmission shift interlock. The switch can only be adjusted once. That is during the initial installation of the switch. If the switch is not adjusted properly or has been removed for some service, a new switch must be installed and adjusted.

Scheme 6

Camshaft Position Sensor

On 2.4L, the camshaft position sensor is mounted on the end of the cylinder head. (Scheme 7) On the 3.3L and the 3.8L, the camshaft position sensor is mounted in the front of the timing case cover. (Scheme 8)

On all applications, the camshaft position sensor provides cylinder identification to the Powertrain Control Module (PCM). (Scheme 9) The sensor generates pulses as groups of notches on the camshaft sprocket pass underneath it. (Scheme 10) The PCM keeps track of crankshaft rotation and identifies each cylinder by the pulses generated by the, notches on the camshaft sprocket. Four crankshaft pulses follow each group of camshaft pulses.

When the PCM receives 2 cam pulses followed by the long flat spot on the camshaft sprocket, it knows that the crankshaft timing marks for cylinder No. 1 are next (on drive plate). When the PCM receives one camshaft pulse after the long flat spot on the sprocket, cylinder No. 2 crankshaft timing marks are next. After 3 camshaft pulses, the PCM knows cylinder No. 4 crankshaft timing marks follow. One camshaft pulse after the 3 pulses indicates cylinder No. 5. The 2 camshaft pulses after cylinder No. 5 signals cylinder No. 6. (Scheme 10) The PCM can synchronize on cylinders No. 1 or 4.

When metal aligns with the sensor, voltage goes low (less than 0.3 volt). When a notch aligns with the sensor, voltage switches high (5 volts). As a group of notches pass under the sensor, the voltage, switches from low (metal) to high (notch) then back to low. The number of notches determine the amount of pulses. If available, an oscilloscope can display the square wave patterns of each timing event.

Top Dead Center (TDC) does not occur when notches on the camshaft sprocket pass below the sensor. TDC occurs after the camshaft pulse (or pulses) and after the 4 crankshaft pulses associated with the particular cylinder. The arrows and cylinder call outs in the illustration represent which cylinder the flat spot and notches identify, they do not indicate TDC position. (Scheme 10)

Scheme 7

Scheme 8

Scheme 9

Scheme 10

Crankshaft Position Sensor

On 2.4L, the crankshaft position sensor is located on the rear of the engine near the accessory drive belt. (Scheme 11) On 3.3L and 3.8L, the crankshaft position sensor is located on the rear of the transmission housing, above the differential housing (Scheme 12) The bottom of the sensor is positioned next to the drive plate. On all applications the crankshaft position sensor detects slots cut into the transmission driveplate extension. (Scheme 13) There are 3 sets of slots. Each set contains 4 slots, for a total of 12 slots. (Scheme 14) Basic timing is set by the position of the last slot in each group. Once the Powertrain Control Module (PCM) senses the last slot, it determines crankshaft position (which piston will next be at TDC) from the camshaft position sensor input. The 4 pulses generated by the crankshaft position sensor represent the 69, 49, 29, and 9 degrees BTDC marks. It may take the PCM one engine revolution to determine crankshaft position. The PCM uses crankshaft position reference to determine injector sequence, ignition timing and the presence of misfire. Once the PCM determines crankshaft position, it begins energizing the injectors in sequence.

Scheme 11

Scheme 12

Scheme 13

Scheme 14

Cruise Control System Switches

Note. Cruise control system may also be referred to as speed control system.

There are 2 separate switch pods that operate the cruise control system and are located on the steering wheel. The cruise control system has 5 separate resistance switches that provide a single multiplexed (MUX) voltage input to the Powertrain Control Module (PCM). The switch names are: On, Off, Set, Coast, Resume, Accel, Tap-up, Coast and Cancel. Based on conditions when the buttons are pushed (and released), the 5 voltage ranges provided to the PCM result in the following functions: On, Off, Set, Coast, Resume, Accel, Tap-Up, Tap-Down, Coast and Cancel. The PCM also receives an input from the brake switch to sense whether the brake pedal has been depressed. When the PCM receives the brake depressed input, it turns off power to the cruise control servo and disengages cruise control. Also the power to the servo is supplied thorough the brake switch, which opens the circuit when the brake pedal is depressed. The individual switches cannot be repaired. If one switch fails, the entire switch module must be replaced.

Data Bus Communication Receive

The Powertrain Control Module (PCM) uses the Serial Communications Interface (SCI) communication bus to preform engine diagnostics and flash operations. The transmission side of the PCM uses the SCI communication bus to flash new software. However, diagnostics is performed via the vehicles J1850 bus for the transmission side of the PCM.

Downstream Oxygen Sensor

Downstream oxygen sensor is a heated oxygen sensor mounted on exhaust pipe behind catalytic converter. (Scheme 15) Heater is used on downstream oxygen sensor so sensor reaches operating temperature quicker and maintains sensor at operating temperature during all operating modes. Heater on downstream oxygen sensor receives voltage from Auto Shutdown (ASD) relay. For operation of ASD relay, see RELAYS under MISCELLANEOUS CONTROLS.

The downstream heated oxygen sensor input is used to detect catalytic converter deterioration. As the converter 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 Powertrain Control Module (PCM) calculates catalytic converter efficiency. Also used to establish the upstream O2 goal voltage (switching point).

Downstream oxygen sensor produces a small electrical voltage input signal to PCM depending on amount of oxygen content in the exhaust gas. Downstream oxygen sensor produces a low voltage when a large amount of oxygen exists in exhaust gas (lean condition) and a higher voltage when a lesser amount of oxygen exists in exhaust gas (rich condition).

PCM uses input signal to monitor catalytic converter. As catalytic converter deteriorates, input signal from downstream oxygen sensor begins to match input signal from upstream oxygen sensor except for a slight time delay. PCM compares input signals from upstream and downstream oxygen sensors to calculate efficiency of catalytic converter. If efficiency of catalytic converter becomes less than specified value, a diagnostic trouble code will be stored in PCM.

Scheme 15

Engine Coolant Temperature Sensor

Engine Coolant Temperature (ECT) sensor delivers input signal to Powertrain Control Module (PCM) to indicate engine coolant temperature. PCM uses input signal for controlling air/fuel ratio, ignition system, idle speed and cooling fan operation. ECT sensor is located on or near the thermostat housing. (Scheme 16)and (Scheme 17).

Scheme 16

Scheme 17

Ignition Sense

The ignition sense input informs the powertrain control module that the ignition switch is in the crank or run position.

Inlet Air Temperature Sensor

The IAT Sensor is a Negative Temperature Coefficient (NTC) Sensor that provides information to the Powertrain Control Module (PCM) regarding the temperature of the air entering the intake manifold. The Intake Air Temperature (IAT) sensor value is used by the PCM to determine air density. The PCM uses this information to calculate, Injector pulse width, Adjustment of ignition timing, to prevent spark knock at high intake air temperatures.

Inlet Air Temperature (IAT) sensor delivers input signal to PCM to indicate temperature of incoming intake air. PCM uses input signal for controlling fuel injector pulse width and spark advance. Inlet air temperature sensor is mounted to inlet air ducting. (Scheme 18)and (Scheme 19).

Scheme 18

Scheme 19

Knock Sensor

The knock sensor threads into the cylinder block. The knock sensor is designed to detect engine vibration that is caused by detonation. When the knock sensor detects a knock in one of the cylinders, it sends an input signal to the Powertrain Control Module (PCM). In response, the PCM retards ignition timing for all cylinders by a scheduled amount. Knock sensors contain a piezoelectric material which constantly vibrates and sends an input voltage signal to the PCM while the engine operates. As the intensity of the crystal's vibration increases, the knock sensor output voltage also increases. The voltage signal produced by the knock sensor increases with the amplitude of vibration. The PCM receives the knock sensor voltage signal as an input. If the signal increases above a predetermined level, the PCM will store that value in memory and retard ignition timing to reduce engine knock. If the knock sensor voltage exceeds a preset value, the PCM retards ignition timing for all cylinders. It is not a selective cylinder retard.

The PCM ignores knock sensor input during engine idle conditions. Once the engine speed exceeds a specified value, knock retard is allowed. Knock retard uses its own short term and long term memory program. Long term memory stores previous detonation information in its battery backed RAM. The maximum authority that long term memory has over timing retard can be calibrated. Short term memory is allowed to retard timing up to a preset amount under all operation conditions (as long as RPM is above the minimum RPM) except at wide open throttle. The PCM, using short term memory, can respond quickly to retard timing when engine knock is detected. Short term memory is lost anytime the ignition key is turned off.

Manifold Absolute Pressure Sensor

The Manifold Absolute Pressure (MAP) sensor is mounted on the intake manifold. (Scheme 20)and (Scheme 21). The MAP serves as a Powertrain Control Module (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 to the MAP sensor from the PCM and returns a voltage signal to the PCM that reflects manifold pressure. The zero pressure reading is 0.5 volt and full scale is 4.5 volts. For a pressure swing of 0-15 psi, the voltage changes 4.0 volts. 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 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, 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 pressure goes down. The first thing that happens as the ignition key is turned on, before reaching the crank position, the PCM powers up, and looks at the MAP voltage. 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 a known-good sensor in your 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. Anytime the PCM sees Wide Open throttle, based upon TP sensor 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

1. Barometric Pressure
2. Engine Load
3. Manifold Pressure
4. Injector Pulse Width
5. Spark Advance Programs.
6. Shift Point Strategies (Via The PCI Bus)
7. Idle Speed
8. Decel Fuel Shutoff

The powertrain control module 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 4.5 volts at sea level to as low as 0.3 volt 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.

Scheme 20

Scheme 21

O2 Sensor

The upstream oxygen sensor threads into the outlet flange of the exhaust manifold. (Scheme 31)and (Scheme 32). The downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic converter. (Scheme 15) A single sensor ground is used for all 4 O2 sensors (6 Cyl.). A separate upstream and downstream grounds are used on the NGC vehicles (4 Cyl.). As vehicles accumulate mileage, the catalytic converter deteriorates. The deterioration results in a less efficient catalyst. To monitor catalytic converter deterioration, the fuel injection system uses two heated oxygen sensors. One sensor upstream of the catalytic converter, one downstream of the converter. The Powertrain Control Module (PCM) compares the reading from the sensors to calculate the catalytic converter oxygen storage capacity and converter efficiency. Also, the PCM uses the upstream heated oxygen sensor input when adjusting injector pulse width. When the catalytic converter efficiency drops below emission standards, the PCM stores a diagnostic trouble code and illuminates the malfunction indicator lamp (MIL). The O2 sensors produce voltages from 0 to 1 volt (this voltage is offset by a constant 2.5 volts on NGC vehicles), depending upon the oxygen content of the exhaust gas. When a large amount of oxygen is present (caused by a lean air/fuel mixture, can be caused by misfire and exhaust leaks), the sensors produces a low voltage. When there is a lesser amount of oxygen present, caused by a rich air/fuel mixture and can be caused by internal engine problems, it produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensors act 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. Maintaining correct sensor temperature at all times 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 O2 sensors 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 pre-programmed (fixed) values and inputs from other sensors.

NGC Controller - Has a common ground for the heater in the O2S, 12 volts are supplied to the heater in the O2S by the NGC controller. Both the upstream and downstream O2 sensors for NGC are Pulse Width Modulation (PWM).

Park/Neutral Switch (Transmission Range Sensor)

The Transmission Range Sensor (TRS) is mounted to the top of the valve body inside the transaxle and can only be serviced by removing the valve body. The electrical connector extends through the transaxle case. (Scheme 22) The TRS has 4 switch contacts that monitor shift lever position and send the information to the Powertrain/Transmission Control Module (PCM/TCM). The TRS communicates shift lever position (SLP) to the PCM/TCM as a combination of open and closed switches. (Scheme 22) Each shift lever position has an assigned combination of switch states (open/closed) that the PCM/TCM receives from 4 sense circuits. The PCM/TCM interprets this information and determines the appropriate transaxle gear position and shift schedule. Since there are 4 switches, there are 16 possible combinations of open and closed switches (codes). Seven of these codes are related to gear position and three are recognized as "between gear" codes. This results in 6 codes which should never occur. These are called "invalid" codes. An invalid code will result in a DTC, and the PCM/TCM will then determine the shift lever position based on pressure switch data. This allows reasonably normal transmission operation with a TRS failure.

Scheme 22

Sensor Return

The sensor return circuit provides a low electrical noise ground reference for all sensors. The sensor return circuit connects to the internal ground circuits within the powertrain control module.

Throttle Position Sensor

Throttle Position (TP) sensor is mounted to the side of the throttle body. (Scheme 23)or (Scheme 24). The sensor connects to the throttle blade shaft. The TP sensor is a variable resistor that provides the Powertrain Control Module (PCM) with an input voltage signal. The signal represents throttle blade position. As the position of the throttle blade changes, the resistance of the TP sensor changes. The PCM supplies approximately 5 volts to the TP sensor. The TP sensor output voltage (input signal to the PCM) represents throttle blade position. The TP sensor 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 TP sensor input to determine current engine operating conditions. The PCM also adjusts fuel injector pulse width and ignition timing based on these inputs.

Scheme 23

Scheme 24

Transmission Control Module

See TRANSMISSION CONTROL MODULE under TRANSMISSION under MISCELLANEOUS CONTROLS.

Transmission Input Speed Sensor

The input speed sensor is a two-wire magnetic pick-up device that generates an AC voltage signal as rotation occurs. (Scheme 25) It is threaded into the transaxle case and sealed with an "O" ring. (Scheme 26) The sensor is considered a primary input to the Powertrain/Transmission Control Module (PCM/TCM). The input speed sensor provides information on how fast the input shaft is rotating. As the teeth of the input clutch hub pass by the sensor coil, an AC voltage signal is generated and sent to the PCM/TCM. (Scheme 27) The PCM/TCM interprets this information as input shaft RPM. The PCM/TCM compares the input speed signal with the output speed signal to determine transmission gear ratio, speed ratio error detection and clutch volume index. The PCM/TCM also compares the input speed signal and the engine speed signal to determine torque converter clutch slippage and torque converter element speed ration.

Scheme 25

Scheme 26

Scheme 27

Transmission Output Speed Sensor

The output speed sensor is a two-wire magnetic pickup device that generates an AC voltage signal as rotation occurs. It is threaded into the transaxle case and sealed with an "O" ring. (Scheme 28)and (Scheme 29). The sensor is considered a primary input to the Powertrain/Transmission Control Module (PCM/TCM). The Output Speed Sensor provides information on how fast the output shaft is rotating. As the rear planetary carrier park pawl lugs pass the sensor coil, an AC voltage is generated and sent to the PCM/TCM. (Scheme 30) The PCM/TCM interprets this information as output shaft RPM. The PCM/TCM compares the input and output speed signals to determine the transmission gear ratio, speed ratio error detection CVI calculation. The vehicle speed signal is taken from the Output Speed Sensor. The PCM converts this signal into a pulse per mile signal and sends the vehicle speed message across the communication bus to the Body Control Module (BCM). The BCM sends this signal to the instrument cluster to display vehicle speed to the driver. The vehicle speed signal pulse is roughly 8000 pulses per mile.

Scheme 28

Scheme 29

Scheme 30

Transmission Range Sensor

Transmission Range (TR) sensor may also be referred to as park/neutral switch. See PARK/NEUTRAL SWITCH (TRANSMISSION RANGE SENSOR) .

Upstream Oxygen Sensor

Upstream oxygen sensor is a heated oxygen sensor mounted on the exhaust manifold. (Scheme 31)and (Scheme 32). Heater is used on upstream oxygen sensor so sensor reaches operating temperature quicker and maintains sensor at operating temperature during all operating modes. Heater on upstream oxygen sensor receives voltage from Auto Shutdown (ASD) relay. For operation of ASD relay, see RELAYS under MISCELLANEOUS CONTROLS.

The input from the upstream heated oxygen sensor tells the Powertrain Control Module (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. The sensor input switches from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold (this is offset by 2.5 voltage on NGC vehicles). 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 heating element in the sensor provides heat to the sensor ceramic element. 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, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with other inputs. In Open Loop, the PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.

Upstream oxygen sensor produces a small electrical voltage input signal to PCM depending on amount of oxygen content in the exhaust gas. Upstream oxygen sensor produces a low voltage when a large amount of oxygen exists in exhaust gas (lean condition) and a higher voltage when a lesser amount of oxygen exists in exhaust gas (rich condition). The heating element in the sensor provides heat to the sensor ceramic element. Heating the sensor allows the system to enter closed-loop operation sooner. It also allows the system to remain in closed-loop operation during periods of extended idle. In closed-loop, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with other inputs. In open-loop, the PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.

Scheme 31

Scheme 32

Vehicle Speed Sensor (VSS)

VSS delivers an input signal to Powertrain Control Module (PCM) to indicate transaxle output shaft speed. PCM uses input signal from VSS, along with TP sensor closed throttle input signal to determine if a closed throttle deceleration or normal idle condition exists. During deceleration, PCM controls Idle Air Control (IAC) motor to maintain a desired MAP value. During idle conditions, PCM controls IAC motor to maintain a desired idle speed.

OUTPUT SIGNALS

Note. Vehicles are equipped with different combinations of computer controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to the system indicated after component.

A/C Clutch Relay

See A/C CLUTCH RELAY under RELAYS under MISCELLANEOUS CONTROLS.

See AUTO SHUTDOWN RELAY under RELAYS under MISCELLANEOUS CONTROLS.

Data Link Connector

See DATA LINK CONNECTOR under SELF-DIAGNOSTIC SYSTEM.

Distributorless Ignition System

See DISTRIBUTORLESS IGNITION SYSTEM under IGNITION SYSTEMS.

EGR Transducer Solenoid

See EXHAUST GAS RECIRCULATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS.

EVAP Purge Solenoid

See EVAPORATIVE EMISSIONS SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS.

Fuel Injectors

See FUEL INJECTORS under FUEL CONTROL under FUEL SYSTEMS.

Fuel Pump

See FUEL PUMP under FUEL DELIVERY under FUEL SYSTEMS.

Fuel Pump Relay

See FUEL PUMP RELAY under FUEL DELIVERY under FUEL SYSTEMS.

Generator Field

See GENERATOR under MISCELLANEOUS CONTROLS.

Idle Air Control Motor

See IDLE SPEED under FUEL SYSTEMS.

Leak Detection Pump

See LEAK DETECTION PUMP SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS.

Malfunction Indicator Light

See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.

Radiator Fan Control Relay

See RADIATOR FAN CONTROL RELAY under RELAYS under MISCELLANEOUS CONTROLS.

Starter Relay

See STARTER RELAY under RELAYS under MISCELLANEOUS CONTROLS.

Tachometer

See TACHOMETER under MISCELLANEOUS CONTROLS.

5-Volt Supply

The PCM supplies 5 volts to the following sensors

1. A/C Pressure Transducer
2. Ambient Temperature Sensor
3. Battery Temperature
4. Camshaft Position Sensor
5. Crankshaft Position Sensor
6. Engine Coolant Temperature Sensor
7. Inlet Air Temperature Sensor
8. Knock Sensor
9. Linear EGR Solenoid (If Equipped)
10. Manifold Absolute Pressure Sensor
11. Oil Pressure Switch
12. Throttle Position Sensor
13. Vehicle Speed Sensor

8-Volt Supply

The Powertrain Control Module supplies 8 volts to the crankshaft position sensor, camshaft position sensor.

FUEL SYSTEMS

Note. The 3.3L is available in 2 models, low-emission model and flex-fuel model. Low-emission model may also be referred to as Low Emission Vehicle (LEV) model and is used for California emission vehicles. Flex-fuel model may also be referred to as Flex-Fuel Vehicle (FFV) model and is used in all vehicles except California emission vehicles. California emission vehicles may be verified by underhood Emission Control label and may be available in other states. Flex-fuel model may be also referred to as an E85 application and may be identified by label attached to inside of gasoline filler door. On flex-fuel models, if test procedure or specification differs from low-emission models, test procedure or specification will be listed separately. If test procedure or specification does not vary, flex-fuel model will be included with low emission model.

FUEL DELIVERY

Note. Fuel system is a returnless design. Fuel pressure regulator is mounted on fuel pump module.

Fuel pump is an in-tank pump mounted at the bottom of fuel pump module, located in top of fuel tank. Fuel pump module also contains fuel pressure regulator and fuel level sensor for fuel gauge. (Scheme 33) Fuel pump is a positive displacement, immersible pump with a permanent magnet electric motor. Fuel is drawn through inlet strainer on bottom of fuel pump module, through fuel pressure regulator, fuel filter, and delivered to fuel rail and fuel injectors. Fuel pump contains an internal check valve in the pump outlet. Check valve is used to maintain fuel pressure when engine and fuel pump are not operating.

The fuel pump has a maximum deadheaded pressure output of about 130 psi (880 kPa). The fuel pressure regulator adjusts fuel system pressure to about 53-63 psi (366-434 kPa). Fuel pump is operated by voltage supplied from fuel pump relay. If the fuel pump or electrical wiring harness requires service, fuel pump module must be replaced.

Scheme 33

The fuel pump relay is located in the PDC. The inside top of the PDC cover has a label showing relay and fuse location.

The fuel pump relay supplies battery voltage to the fuel pump. A buss bar in the PDC supplies voltage to the solenoid side and contact side of the relay. The fuel pump relay power circuit contains a fuse between the buss bar in the PDC and the relay. The fuse is located in the PDC. The Powertrain Control Module (PCM) controls the fuel pump relay by switching the ground path for the solenoid side of the relay on and off. The PCM turns the ground path off when the ignition switch is in the Off position. When the ignition switch is in the On position, the PCM energizes the fuel pump. If the crankshaft position sensor does not detect engine rotation, the PCM de-energizes the relay after approximately one second.

Fuel Pressure Regulator

Fuel pressure regulator is a nonadjustable in-tank pressure regulator mounted on the fuel pump module on top of fuel tank. (Scheme 33) Fuel pressure regulator maintains fuel system pressure at about 53-63 psi (365-434 kPa). The fuel pressure regulator consists of a diaphragm, calibrated spring and a fuel return valve. Calibrated spring pushes downward on the diaphragm and closes off the fuel return port. System fuel pressure reflects the amount of fuel pressure required to open the fuel return port. When fuel return valve opens, excess fuel is returned to the fuel tank. The fuel pressure regulator is a mechanical device that is not controlled by the Powertrain Control Module or engine vacuum.

Auto Shutdown (ASD) relay provides voltage to fuel injectors. See AUTO SHUTDOWN RELAY under RELAYS under MISCELLANEOUS CONTROLS.

The fuel injectors are positioned in the intake manifold or cylinder head with the nozzle ends directly above the intake valve port. (Scheme 34) The fuel injectors are 12-volt electrical solenoids. (Scheme 35) 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 a hollow cone or two streams. The spraying action atomizes the fuel, adding it to the air entering the combustion chamber. Fuel injectors are not interchangeable between engines. The Powertrain Control Module (PCM) provides battery voltage to each injector through the Auto Shutdown (ASD) relay. Injector operation is controlled by a ground path provided for each injector by the PCM. Injector on-time (pulse width) is variable, and is determined by the PCM processing all the data previously discussed to obtain the optimum injector pulse width for each operating condition. The pulse width is controlled by the duration of the ground path provided.

Scheme 34

Scheme 35

Idle Air Control (IAC) motor is mounted on throttle body. (Scheme 18)and (Scheme 36). The Powertrain Control Module (PCM) controls idle speed by use of IAC motor to compensate for engine load, coolant temperature or barometric pressure changes. The throttle body has an air by-pass passage that provides air for the engine during closed throttle idle. The IAC motor pintle protrudes into the air by-pass passage and regulates air flow through it. The PCM adjusts engine idle speed by moving the IAC motor pintle in and out of the by-pass 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, A/C). When engine RPM is above idle speed, the IAC motor is used for off-idle dashpot, deceleration air flow control and 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).

Scheme 36

Throttle Body

The throttle body is located on the intake manifold. (Scheme 18)or (Scheme 36). 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.

MODES OF OPERATION

As input signals to the Powertrain Control Module (PCM) change, the PCM adjusts its response to output devices. For example, the PCM must calculate a different injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT). There are several different modes of operation that determine how the PCM responds to the various input signals.

There are two different areas of operation, OPEN LOOP and CLOSED LOOP.

During OPEN LOOP modes the PCM receives input signals and responds according to preset PCM programming. Inputs from the upstream and downstream heated oxygen sensors are not monitored during OPEN LOOP modes, except for heated oxygen sensor diagnostics (they are checked for shorted conditions at all times).

During CLOSED LOOP modes the PCM monitors the inputs from the upstream and downstream heated oxygen sensors. The upstream heated oxygen sensor input tells the PCM if the calculated injector pulse width resulted in the ideal air/fuel ratio of 14.7 to one. By monitoring the exhaust oxygen content through the upstream heated oxygen sensor, the PCM can fine tune injector pulse width. Fine tuning injector pulse width allows the PCM to achieve optimum fuel economy combined with low emissions.

For the PCM to enter CLOSED LOOP operation, the following must occur

1. Engine coolant temperature must be over 35°F. If the coolant is over 35°F the PCM will wait 38 seconds. If the coolant is over 50°F the PCM will wait 15 seconds. If the coolant is over 167°F the PCM will wait 3 seconds.
2. For other temperatures the PCM will interpolate the correct waiting time.
3. O2 sensor must read either greater than 0.745 volt or less than 0.29 volt.
4. The multi-port fuel injection systems has the following modes of operation: Ignition Switch ON (Zero RPM) Engine Start-Up Engine Warm-Up Cruise Idle Acceleration Deceleration Wide Open Throttle Ignition Switch OFF
5. The engine start-up (crank), engine warm-up, deceleration with fuel shutoff and wide open throttle modes are OPEN LOOP modes. Under most operating conditions, the acceleration, deceleration (with A/C on), idle and cruise modes, with the engine at operating temperature are CLOSED LOOP modes.

Ignition Switch On (Zero RPM) Mode

When the ignition switch activates the fuel injection system, the following actions occur

1. The Powertrain Control Module (PCM) monitors the engine coolant temperature sensor and throttle position sensor input. The PCM determines basic fuel injector pulse width from this input.
2. The PCM determines atmospheric air pressure from the MAP sensor input to modify injector pulse width. When the key is in the ON position and the engine is not running (zero RPM), the Auto Shutdown (ASD) and fuel pump relays de-energize after approximately one second. Therefore, battery voltage is not supplied to the fuel pump, ignition coil, fuel injectors and heated oxygen sensors.

Engine Start-Up Mode

This is an OPEN LOOP mode. If the vehicle is in park or neutral (automatic transaxles) or the clutch pedal is depressed (manual, transaxles) the ignition switch energizes the starter relay when the engine is not running. The following actions occur when the starter motor is engaged.

1. If the Powertrain Control Module (PCM) receives the camshaft position sensor and crankshaft position sensor signals, it energizes the Auto Shutdown (ASD) relay and fuel pump relay. If the PCM does not receive both signals within approximately one second, it will not energize the ASD relay and fuel pump relay. The ASD and fuel pump relays supply battery voltage to the fuel pump, fuel injectors, ignition coil, (EGR solenoid and PCV heater if equipped) and heated oxygen sensors.
2. The PCM energizes the injectors (on the 69 degree falling edge) for a calculated pulse width until it determines crankshaft position from the camshaft position sensor and crankshaft position sensor signals. The PCM determines crankshaft position within 1 engine revolution.
3. After determining crankshaft position, the PCM begins energizing the injectors in sequence. It adjusts injector pulse width and controls injector synchronization by turning the individual ground paths to the injectors ON and OFF.
4. When the engine idles within +/- 64 RPM of its target RPM, the PCM compares current MAP sensor value with the atmospheric pressure value received during the Ignition Switch On (zero RPM) mode.

Once the ASD relay and fuel pump relays have been energized, the PCM determines injector pulse width based on the following

1. MAP
2. Engine RPM
3. Battery Voltage
4. Engine Coolant Temperature
5. Inlet/Intake Air Temperature (IAT)
6. Throttle Position
7. The number of engine revolutions since cranking was initiated.

During Start-up the PCM maintains ignition timing at 9 degrees BTDC.

Engine Warm-Up Mode

This is an OPEN LOOP mode. The following inputs are received by the Powertrain Control Module (PCM)

1. Manifold Absolute Pressure
2. Crankshaft Position (Engine Speed)
3. Engine Coolant Temperature
4. Inlet/Intake Air Temperature
5. Camshaft Position
6. Knock Sensor
7. Throttle Position
8. A/C Switch Status
9. Battery Voltage
10. Vehicle Speed
11. Speed Control
12. O2 Sensors

The PCM adjusts injector pulse width and controls injector synchronization by turning the individual ground paths to the injectors ON and OFF.

The PCM adjusts ignition timing and engine idle speed. Engine idle speed is adjusted through the idle air control motor.

Cruise Or Idle Mode

When the engine is at operating temperature this is a CLOSED LOOP mode. During cruising or idle the following inputs are received by the Powertrain Control Module (PCM)

1. Manifold Absolute Pressure
2. Crankshaft Position (Engine Speed)
3. Inlet/Intake Air Temperature
4. Engine Coolant Temperature
5. Camshaft Position
6. Knock Sensor
7. Throttle Position
8. Exhaust Gas Oxygen Content (O2 Sensors)
9. A/C Switch Status Battery Voltage
10. Vehicle Speed

The PCM adjusts injector pulse width and controls injector synchronization by turning the individual ground paths to the injectors ON and OFF.

The PCM adjusts engine idle speed and ignition timing. The PCM adjusts the air/fuel ratio according to the oxygen content in the exhaust gas (measured by the, upstream and downstream heated oxygen sensor).

The PCM monitors for engine misfire. During active misfire and depending on the severity, the PCM either continuously illuminates or flashes the malfunction indicator lamp (Check Engine light on instrument panel). Also, the PCM stores an engine misfire DTC in memory, if 2nd trip with fault.

The PCM performs the following diagnostic routines.

1. Oxygen sensor monitor.
2. Downstream heated oxygen sensor diagnostics during open loop operation (except for shorted).
3. Fuel system monitor.
4. EGR monitor (if equipped) purge system monitor.
5. Catalyst efficiency monitor.
6. All inputs monitored for proper voltage range, rationality.
7. All monitored components (refer to the Emission section for On-Board Diagnostics).

The PCM compares the upstream and downstream heated oxygen sensor inputs to measure catalytic converter efficiency. If the catalyst efficiency drops below the minimum acceptable percentage, the PCM stores a diagnostic trouble code in memory, after 2 trips.

During certain idle conditions, the PCM may enter a variable idle speed strategy. During variable idle speed strategy the PCM adjusts engine speed based on the following inputs

1. A/C Status
2. Battery Voltage
3. Battery Temperature Or Calculated Battery Temperature
4. Engine Coolant Temperature
5. Engine Run Time
6. Inlet/Intake Air Temperature
7. Vehicle Mileage

Acceleration Mode

This is a CLOSED LOOP mode. The Powertrain Control Module (PCM) recognizes an abrupt increase in Throttle Position sensor output voltage or MAP sensor, output voltage as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased fuel demand.

Deceleration Mode

This is a CLOSED LOOP mode. During deceleration the following inputs are received by the Powertrain Control Module (PCM)

1. A/C Status
2. Battery Voltage
3. Inlet/Intake Air Temperature
4. Engine Coolant Temperature
5. Crankshaft Position (Engine Speed)
6. Exhaust Gas Oxygen Content (Upstream Heated Oxygen Sensor)
7. Knock Sensor
8. Manifold Absolute Pressure
9. Throttle Position Sensor
10. IAC motor (solenoid) control changes in response to MAP sensor feedback.

The PCM may receive a closed throttle input from the Throttle Position sensor (TP) when it senses an abrupt decrease in manifold pressure. This indicates a hard deceleration (Open Loop). In response, the PCM may momentarily turn off the injectors. This helps improve fuel economy, emissions and engine braking.

Wide Open Throttle Mode

This is an OPEN LOOP mode. During Wide Open Throttle operation, the following inputs are used by the Powertrain Control Module (PCM)

1. Inlet/Intake Air Temperature
2. Engine Coolant Temperature
3. Engine Speed
4. Knock Sensor
5. Manifold Absolute Pressure
6. Throttle Position

When the PCM senses a Wide Open Throttle condition through the Throttle Position sensor (TP) it de-energizes the A/C compressor clutch relay. This disables the air conditioning system and disables EGR (if equipped).

The PCM adjusts injector pulse width to supply a predetermined amount of additional fuel, based on MAP and RPM.

Ignition Switch Off Mode

When the operator turns the ignition switch to the OFF position, the following occurs

1. All outputs are turned off, unless O2 Heater Monitor test is being run.
2. No inputs are monitored except for the heated oxygen sensors. The powertrain control module monitors the heating elements in the oxygen sensors and then shuts down.

IGNITION SYSTEMS

Note. All engines use a fixed ignition timing system. Basic ignition timing is not adjustable. All spark advance is determined by the powertrain control module.

The distributorless ignition system used on these engines is referred to as the Direct Ignition System (DIS). The system's three main components are the coil pack, crankshaft position sensor, and the camshaft position sensor. If equipped with the coil on plug ignition system it utilizes an ignition coil for every cylinder, it is mounted directly over the each spark plug. The crankshaft position sensor and camshaft position sensor are Hall Effect devices. The camshaft position sensor and crankshaft position sensor generate pulses that are inputs to the Powertrain Control Module (PCM). The PCM determines engine position from these sensors. The PCM calculates injector sequence and ignition timing from crankshaft and camshaft position. For a description of both crankshaft and camshaft position sensors, see INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.

EVAPORATIVE EMISSIONS SYSTEM

The evaporation control system prevents the emission of fuel tank vapors into the atmosphere. When fuel evaporates in the fuel tank, the vapors pass through vent hoses or tubes to a charcoal filled evaporative canister. The canister temporarily holds the vapors. See EVAP CANISTER . The Powertrain Control Module (PCM) allows intake manifold vacuum to draw vapors into the combustion chambers during certain operating conditions. All engines use a proportional purge solenoid system. The PCM controls vapor flow by operating the purge solenoid. See EVAP CANISTER PURGE SOLENOID . On 2.4L, natural vacuum leak detection system is used as part of the evaporative system for OBD-II requirements. See NATURAL VACUUM LEAK DETECTION (2.4L) . On 3.3L and 3.8L, a Leak Detection Pump (LDP) is used as part of the evaporative system for OBD-II requirements. See LEAK DETECTION PUMP SYSTEM . Vehicle is also equipped with On-Board Refueling Vapor Recovery (ORVR). See ON-BOARD REFUELING VAPOR RECOVERY . The evaporative system uses specially manufactured lines/hoses. If replacement becomes necessary, only use fuel resistant, low permeation hose.

EVAP Canister

Two maintenance free EVAP charcoal canisters are used. (Scheme 37) The vacuum and vapor tubes connect to the top of the canister. Fuel tank vapors vent into the canister. The canister temporarily holds the fuel vapors until the intake manifold vacuum draws them into the combustion chamber. The Powertrain Control Module (PCM) purges the canister through the proportional purge solenoid. The PCM purges the canister at predetermined intervals and engine conditions. Purge-free memory cells are used to identify the fuel vapor content of the EVAP canister. Since the EVAP canister is not purged 100 percent of the time, the PCM stores information about the EVAP canister's vapor content in a memory cell.

The purge-free cells are constructed similar to certain purge-normal cells. The purge-free cells can be monitored by using the DRBIII(R) scan tool. The only difference between the purge-free cells and normal adaptive cells is that in purge-free, the purge is completely turned off. This gives the PCM the ability to compare purge and purge-free operation.

Scheme 37

EVAP Canister Purge Solenoid

All vehicles use a proportional purge solenoid. (Scheme 38) The solenoid regulates the rate of vapor flow from the EVAP canister to the throttle body. The Powertrain Control Module (PCM) operates the solenoid. During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged. The purge solenoid operates at a frequency of 200 Hz and is controlled by an engine controller circuit that senses the current being applied to the purge solenoid and then adjusts that current to achieve the desired purge flow. The purge solenoid controls the purge rate of fuel vapors from the vapor canister and fuel tank to the engine intake manifold.

Scheme 38

Fuel Filler Cap

The plastic fuel tank filler cap is threaded/quarter turn onto the end of the fuel filler tube. Its purpose is to retain vapors and fuel in the fuel tank. The fuel filler cap incorporates a two-way relief valve that is closed to atmosphere during normal operating conditions. The relief valve is calibrated to open when a pressure of 2.5 psi (17 kPa) or vacuum of 2 kPa (0.6 in. Hg) occurs in the fuel tank. When the pressure or vacuum is relieved, the valve returns to the normally closed condition. Remove filler cap before servicing any fuel system component to relieve tank pressure. If equipped with a California emissions package and a Leak Detection Pump (LDP), the cap must be tightened securely. If cap is left loose, a Diagnostic Trouble Code (DTC) may be set.

EXHAUST GAS RECIRCULATION SYSTEM

The Exhaust Gas Recirculation (EGR) system consists of EGR tube (connects a passage in the intake manifold to the exhaust port in the cylinder head), EGR valve, electric EGR transducer and connecting hoses. (Scheme 39), (Scheme 40) and (Scheme 41). The EGR system reduces Oxides of Nitrogen (NOx) in engine exhaust and helps prevent detonation (engine knock). Under normal operating conditions, engine cylinder temperature can reach more than 3000°F. Formation of NOx increases proportionally with combustion temperature. To reduce the emission of these oxides, the cylinder temperature must be lowered. The system allows a predetermined amount of hot exhaust gas to recirculate and dilute the incoming air/fuel mixture. The diluted air/fuel mixture reduces peak flame temperature during combustion. The electric EGR transducer contains an electrically operated solenoid and a back-pressure transducer. (Scheme 41) The Powertrain Control Module (PCM) operates the solenoid and determines when to energize the solenoid. Exhaust system back-pressure controls the transducer.

When the PCM energizes the solenoid, vacuum does not reach the transducer. Vacuum flows to the transducer when the PCM de-energizes the solenoid. When exhaust system back-pressure becomes high enough, it fully closes a bleed valve in the transducer. When the PCM de-energizes the solenoid and back-pressure closes the transducer bleed valve, vacuum flows through the transducer to operate the EGR valve. De-energizing the solenoid, but not fully closing the transducer bleed hole (because of low back-pressure), varies the strength of vacuum applied to the EGR valve. Varying the strength of the vacuum changes the amount of EGR supplied to the engine. This provides the correct amount of exhaust gas recirculation for different operating conditions. This system does not allow EGR at idle. A failed or malfunctioning EGR system can cause engine spark knock, sags or hesitation, rough idle, engine stalling and increased emissions.

Scheme 39

Scheme 40

Scheme 41

LEAK DETECTION PUMP SYSTEM (3.3L & 3.8L)

The Evaporative (EVAP) emission system is designed to prevent the escape of fuel vapors from the fuel system. (Scheme 42) Leaks in the system, even small ones, can allow fuel vapors to escape into the atmosphere. Government regulations require on-board testing to make sure that the EVAP system is functioning properly. The leak detection system tests for EVAP system leaks and blockage. It also performs self-diagnostics. During self-diagnostics, the Powertrain Control Module (PCM) first checks the Leak Detection Pump (LDP) for electrical and mechanical faults. The LDP is located below driver's side of steering gear, above engine cradle. (Scheme 43) If the first checks pass, the PCM then uses the LDP to seal the vent valve and pump air into the system to pressurize it. If a leak is present, the PCM will continue pumping the LDP to replace the air that leaks out. The PCM determines the size of the leak based on how fast/long it must pump the LDP as it tries to maintain pressure in the system. EVAP leak detection system components are described as follows.

1. Service Port Used with special tools like the Miller Evaporative Emissions Leak Detector (EELD) to test for leaks in the system.
2. EVAP Purge Solenoid The PCM uses the EVAP purge solenoid to control purging of excess fuel vapors stored in the EVAP canister. It remains closed during leak testing to prevent loss of pressure.
3. EVAP Canister The EVAP canister stores fuel vapors from the fuel tank for purging.
4. EVAP Purge Orifice Limits purge volume.
5. EVAP System Air Filter Provides air to the LDP for pressurizing the system. It filters out dirt while allowing a vent to atmosphere for the EVAP system.

The main purpose of the LDP is to pressurize the fuel system for leak checking. It closes the EVAP system vent to atmospheric pressure so the system can be pressurized for leak testing. The diaphragm is powered by engine vacuum. It pumps air into the EVAP system to develop a pressure of about 7.5 in. H2O (1/4 psi). A reed switch in the LDP allows the PCM to monitor the position of the LDP diaphragm. The PCM uses the reed switch input to monitor how fast the LDP is pumping air into the EVAP system. This allows detection of leaks and blockage. The LDP assembly consists of several parts. (Scheme 44) The solenoid is controlled by the PCM and it connects the upper pump cavity to either engine vacuum or atmospheric pressure. A vent valve closes the EVAP system to atmosphere, sealing the system during leak testing. The pump section of the LDP consists of a diaphragm that moves up and down to bring air in through the air filter and inlet check valve, and pump it out through an outlet check valve into the EVAP system. The diaphragm is pulled up by engine vacuum, and pushed down by spring pressure as the LDP solenoid turns on and off. The LDP also has a magnetic reed switch to signal diaphragm position to the PCM. When the diaphragm is down, the switch is closed, which sends a 12 volt (system voltage) signal to the PCM. When the diaphragm is up, the switch is open, and there is no voltage sent to the PCM. This allows the PCM to monitor LDP pumping action as it turns the LDP solenoid on and off.

Scheme 42

Scheme 43

Scheme 44

LDP At Rest (Not Powered)

When the Leak Detection Pump (LDP) is at rest (no electrical/vacuum) the diaphragm is allowed to drop down if the internal (EVAP system) pressure is not greater than the return spring. The LDP solenoid blocks the engine vacuum port and opens the atmospheric pressure port connected through the EVAP system air filter. The vent valve is held open by the diaphragm. This allows the canister to see atmospheric pressure. (Scheme 45)

Scheme 45

Diaphragm Upward Movement

When the Powertrain Control Module (PCM) energizes the Leak Detection Pump (LDP) solenoid, the solenoid blocks the atmospheric port leading through the EVAP air filter and at the same time opens the engine vacuum port to the pump cavity above the diaphragm. The diaphragm moves upward when vacuum above the diaphragm exceeds spring force. This upward movement closes the vent valve. It also causes low pressure below the diaphragm, unseating the inlet check valve and allowing air in from the EVAP air filter. When the diaphragm completes its upward movement, the LDP reed switch turns from closed to open. (Scheme 46)

Scheme 46

Diaphragm Downward Movement

Based on reed switch input, the Powertrain Control Module (PCM) de-energizes the Leak Detection Pump (LDP) solenoid, causing it to block the vacuum port, and open the atmospheric port. This connects the upper pump cavity to atmosphere through the EVAP air filter. The spring is now able to push the diaphragm down. The downward movement of the diaphragm closes the inlet check valve and opens the outlet check valve pumping air into the evaporative system. The LDP reed switch turns from open to closed, allowing the PCM to monitor LDP pumping (diaphragm up/down) activity. (Scheme 47) During the pumping mode, the diaphragm will not move down far enough to open the vent valve. The pumping cycle is repeated as the solenoid is turned on and off. When the evaporative system begins to pressurize, the pressure on the bottom of the diaphragm will begin to oppose the spring pressure, slowing the pumping action. The PCM watches the time from when the solenoid is de-energized, until the diaphragm drops down far enough for the reed switch to change from opened to closed. If the reed switch changes too quickly, a leak may be indicated. The longer it takes the reed switch to change state, the tighter the evaporative system is sealed. If the system pressurizes too quickly, a restriction somewhere in the EVAP system may be indicated.

Scheme 47

Pumping Action

During portions of this test, the Powertrain Control Module (PCM) uses the reed switch to monitor diaphragm movement. The solenoid is only turned on by the PCM after the reed switch changes from open to closed, indicating that the diaphragm has moved down. At other times during the test, the PCM will rapidly cycle the Leak Detection Pump (LDP) solenoid on and off to quickly pressurize the system. During rapid cycling, the diaphragm will not move enough to change the reed switch state. In the state of rapid cycling, the PCM will use a fixed time interval to cycle the solenoid. If the system does not pass the EVAP Leak Detection Test, the following DTCs may be set

1. P0442: EVAP Leak Monitor 0.040" Leak Detected
2. P0455: EVAP Leak Monitor Large Leak Detected
3. P0456: EVAP Leak Monitor 0.020" Leak Detected
4. P1486: EVAP Leak Monitor Pinched Hose Found
5. P1494: Leak Detection Pump SW Or Mechanical Fault
6. P1495: Leak Detection Pump Solenoid Circuit

EVAP Leak Detection Test Enabling Conditions

1. Cold start with ambient temperature (obtained from modeling the inlet air temperature sensor) between 40°F (4°C) and 90°F (32°C) for 0.040" leak. Between 40°F (4°C) and 85°F (29°) for 0.020" leak.
2. Engine coolant temperature is within 10-18° F (-8 to -12°C) of ambient.
3. Battery voltage is 10-15 volts.
4. Low fuel warning light off (fuel level must be 15-85 percent).
5. MAP sensor reading is 22 in. Hg or above. This is the manifold absolute pressure, not vacuum.
6. No engine stall during test.

Note. If battery voltage drops below 10 volts for more than 5 seconds during engine cranking, the EVAP leak detection test will not run.

A DTC will not be set is a one trip fault is set or is the MIL is illuminated for any of the following

1. Purge Solenoid
2. All TP Sensor Faults
3. All Engine Controller Self-Test Faults
4. LDP Pressure Switch Fault
5. All Camshaft And/Or Crankshaft Sensor Faults
6. EGR Solenoid Electrical Fault
7. MAP Sensor Faults
8. All Injector Faults
9. Ambient Temperature Sensor Electrical Faults
10. BARO Out of Range
11. Vehicle Speed Faults
12. All Coolant Sensor Faults
13. LDP Solenoid Circuit

Note. If battery temperature is not within range, or if the engine coolant temperature is not within a specified range of the battery temperature, the powertrain control module will not run tests for DTC P0441, P0442, P0455, P1486 or P1494. These temperature calibrations may be different between models.

Section 1 - P1495 Leak Detection Pump Solenoid Circuit

Section 1 refers to section 1 in the EVAP Leak Detection Pump (LDP) Test Sequence. (Scheme 48) When the ignition key is turned on, the LDP diaphragm should be in the down position and the LDP reed switch should be closed. If the EVAP system has residual pressure, the LDP diaphragm may be up. This could result in the LDP reed switch being open when the key is turned on and a DTC P1494 fault could be set because the Powertrain Control Module (PCM) is expecting the reed switch to be closed. After the ignition key is turned on, the PCM immediately tests the LDP solenoid circuit for electrical faults. If a fault is detected, DTC P1495 will set, the MIL will illuminate, and the remaining EVAP Leak Detection Test is canceled.

Scheme 48

Section 2 - P1494 Leak Detection Pump Switch Or Mechanical Fault

Section 2 refers to section 2 in the EVAP Leak Detection Pump (LDP) Test Sequence. (Scheme 48) If DTC P1495 is not set, the Powertrain Control Module (PCM) will check for DTC P1494. If the LDP reed switch was closed when the ignition key was turned on, the PCM energizes the LDP solenoid for up to 8 seconds and monitors the LDP switch. As the LDP diaphragm is pulled up by engine vacuum, the LDP reed switch should change from closed to open. If it does not, the PCM sets a temporary fault (DTC P1494) in memory, and waits until the next time the Enabling Conditions are met to run the test again. If this is again detected, DTC P1494 is stored and the MIL is illuminated. If the problem is not detected during the next enabling cycle, the temporary fault will be cleared. However, if the PCM detects the reed switch open when the ignition key is turned on, the PCM must determine if this condition is due to residual pressure in the EVAP system, or an actual fault. The PCM stores information in memory on EVAP system purging from previous engine run or drive cycles. If little or no purging took place, residual pressure could be holding the LDP diaphragm up, causing the LDP switch to be open. Since this is not a malfunction, the PCM cancels the EVAP Leak Detection Test without setting the temporary fault. If there was sufficient purging during the previous cycle to eliminate EVAP system pressure, the PCM judges that this is a malfunction and sets a temporary fault in memory. The next time that the Enabling Conditions are met, the test will run again. If the fault is again detected, the MIL will illuminate and DTC P1494 will be stored. If the fault is not detected, the temporary fault will be cleared.

Section 3 - P1486 EVAP Leak Monitor Pinched Hose Found

Section 3 refers to section 3 in the EVAP Leak Detection Pump (LDP) Test Sequence. (Scheme 48) If no fault has been detected so far, the Powertrain Control Module (PCM) begins testing for possible blockage in the EVAP system between the LDP and the fuel tank. This is done by monitoring the time required for the LDP to pump air into the EVAP system during two to three pump cycles. If no blockage is present, the LDP diaphragm is able to quickly pump air out of the LDP each time the PCM turns off the LDP solenoid. If a blockage is present, the PCM detects that the LDP takes longer to complete each pump cycle. If the pump cycles take longer than expected (approximately 6 to 10 seconds) the PCM will suspect a blockage. On the next drive when Enabling Conditions are met, the test will run again. If blockage is again detected, DTC P1486 is stored, and the MIL is illuminated.

Section 4 - No DTC Can Be Set During This Time

Section 4 refers to section 4 in the EVAP Leak Detection Pump (LDP) Test Sequence. (Scheme 48) After the LDP blockage tests are completed, the Powertrain Control Module (PCM) then tests for EVAP system leakage. First, the PCM commands the LDP to rapidly pump for 20 to 50 seconds (depending on fuel level) to build pressure in the EVAP system. This evaluates the system to see if it can be sufficiently pressurized. This evaluation (rapid pump cycling) may occur several times prior to leak checking. The LDP reed switch does not close and open during rapid pumping because the diaphragm does not travel through its full range during this part of the test.

Section 5 - DTC P0456, P0442, P0455 EVAP Leak Monitor & Leak Detected

Section 5 refers to section 5 in the EVAP Leak Detection Pump (LDP) Test Sequence. (Scheme 48) Next, the Powertrain Control Module (PCM) performs one or more test cycles by monitoring the time required for the LDP reed switch to close (diaphragm to drop) after the LDP solenoid is turned off. If the switch does not close, or closes after a long delay, it means that the system does not have any significant leakage and the EVAP Leak Detection Test is complete. However, if the LDP reed switch closes quickly, there may be a leak or the fuel level may be low enough that the LDP must pump more to finish pressurizing the EVAP system. In this case, the PCM will rapidly pump the LDP again to build pressure in the EVAP system, and follow that by monitoring the time needed for several LDP test cycles. This process of rapid pumping followed by several LDP test cycles may repeat several times before the PCM judges that a leak is present. When leaks are present, the LDP test cycle time will be inversely proportional to the size of the leak. The larger the leak, the shorter the test cycle time. The smaller the leak, the longer the test cycle time. DTCs may be set when a leak as small as 0.020" (0.5 mm) diameter is present. If the system detects a leak, a temporary fault will be stored in PCM memory. The time it takes to detect a 0.020", 0.040", or larger leak is based on calibrations that vary from model to model. The important point to remember is if a leak is again detected on the next EVAP Leak Detection Test, the MIL will illuminate and a DTC will be stored based on the size of leak detected. If no leak is detected during the next test, the temporary fault will be cleared.

Diagnostic Tips

During diagnosis, you can compare the Leak Detection Pump (LDP) solenoid activity with the monitor sequence. (Scheme 48) If the Powertrain Control Module (PCM) detects a problem that could set a DTC, the testing is halted and LDP solenoid activity will stop. As each section of the test begins, it indicates that the previous section passed successfully. By watching to see which tests complete, you can see if any conditions are present that the PCM considers abnormal. For example, if the LDP solenoid is energized for the test cycles to test for blockage (DTC P1486), it means that the LDP has already passed its test for DTC P1494. Then, if the PCM detects a possible blockage, it will set a temporary fault without turning on the MIL and continue the leak portion of the test. However, the PCM will assume that the system is already pressurized and skip the rapid pump cycles. Always diagnose leaks, if possible, before disconnecting connections. Disconnecting connections may mask a leak condition. Keep in mind that if the purge solenoid seat is leaking, it could go undetected since the leak would end up in the intake manifold. Disconnect the purge solenoid at the manifold when leak checking. In addition, a pinched hose fault (DTC P1486) could set if the purge solenoid does not purge the fuel system properly (blocked seat). The purge solenoid must vent the fuel system prior to the LDP system test. If the purge solenoid cannot properly vent the system, the LDP cannot properly complete the test for DTC P1486 and this fault can set due to pressure being in the EVAP system during the test sequence. Multiple actuation's of the DRBIII(R) scan tool Leak Detection Pump Monitor Test can hide a 0.020" leak because of excess vapor generation. Additionally, any source for additional vapor generation can hide a small leak in the EVAP system. Excess vapor generation can delay the fall of the LDP diaphragm thus hiding the small leak. An example of this condition could be bringing a cold vehicle into a warm shop for testing or high ambient temperatures. Fully plugged and partially plugged underhood vacuum lines have been known to set MIL conditions. DTCs P0456 and P1494 can be set for this reason. Always, thoroughly check hoses for pinches or blockage before condemning components.

Test Equipment

The Miller Evaporative Emission Leak Detector (EELD) (8404) is capable of visually detecting leaks in the evaporative system and will take the place of the Ultrasonic Leak Detector (6917A). The EELD utilizes shop air and a smoke generator to visually detect leaks down to 0.020" or smaller. The food grade oil used to make the smoke includes an ultraviolet trace dye that will leave telltale signs of the leak under a Black light. This is helpful when components have to be removed to determine the exact leak location. For detailed test instructions, follow the operators manual packaged with the EELD.

NATURAL VACUUM LEAK DETECTION (2.4L)

The Natural Vacuum Leak Detection (NVLD) system is the next generation evaporative leak detection system that will first be used on vehicles equipped with the Next Generation Controller (NGC). (Scheme 49) This new system replaces the leak detection pump as the method of evaporative system leak detection. This is to detect a leak equivalent to a 0.020" (0.5 mm) hole. This system has the capability to detect holes of this size very dependably. The basic leak detection theory employed with NVLD is the "Gas Law". This is to say that the pressure in a sealed vessel will change if the temperature of the gas in the vessel changes. The vessel will only see this effect if it is indeed sealed. Even small leaks will allow the pressure in the vessel to come to equilibrium with the ambient pressure. In addition to the detection of very small leaks, this system has the capability of detecting medium as well as large evaporative system leaks.

The NVLD seals the canister vent during engine off conditions. If the EVAP system has a leak of less than the failure threshold, the evaporative system will be pulled into a vacuum, either due to the cool down from operating temperature or diurnal (constant) ambient temperature cycling. The diurnal effect, is considered one of the primary contributors to the leak determination by this diagnostic. When the vacuum in the system exceeds about 1 in. H2O (0.25 kPa), a vacuum switch closes. The switch closure sends a signal to the NGC. The NGC, via appropriate logic strategies (described below), utilizes the switch signal, or lack thereof, to make a determination of whether a leak is present.

The NVLD device is designed with a normally open vacuum switch, a normally closed solenoid, and a seal, which is actuated by both the solenoid and a diaphragm. The NVLD is located on the atmospheric vent side of the canister. The NVLD assembly may be mounted on top of the canister outlet, or in-line between the canister and atmospheric vent filter. The normally open vacuum switch will close with about 1 in. H2O (0.25 kPa) vacuum in the evaporative system. The diaphragm actuates the switch. This is above the opening point of the fuel inlet check valve in the fill tube so cap off leaks can be detected. Submerged fill systems must have recirculation lines that do not have the in-line normally closed check valve that protects the system from failed nozzle liquid ingestion, in order to detect cap off conditions.

The normally closed valve in the NVLD is intended to maintain the seal on the evaporative system during the engine off condition. If vacuum in the evaporative system exceeds 3-6 in. H2O (0.75-1.5 kPa), the valve will be pulled off the seat, opening the seal. This will protect the system from excessive vacuum as well as allowing sufficient purge flow in the event that the solenoid was to become inoperative. The solenoid actuates the valve to unseal the canister vent while the engine is running. It also will be used to close the vent during the medium and large leak tests and during the purge flow check. This solenoid requires initial 1.5 amps of current to pull the valve open but after 100 ms will be duty cycled down to an average of about 150 mA for the remainder of the drive cycle.

Another feature in the device is a diaphragm that will open the seal in the NVLD with pressure in the evaporative system. The device will "blow off" at about 0.5 in. H2O (0.12 kPa) pressure to permit the venting of vapors during refueling. An added benefit to this is that it will also allow the tank to "breathe" during increasing temperatures, thus limiting the pressure in the tank to this low level. This is beneficial because the induced vacuum during a subsequent declining temperature will achieve the switch closed (pass threshold) sooner than if the tank had to decay from a built up pressure. The device itself has 3 wires: Switch sense, solenoid driver and ground. It also includes a resistor to protect the switch from a short to battery or a short to ground. The NGC utilizes a high-side driver to energize and duty-cycle the solenoid.

Scheme 49

ON-BOARD REFUELING VAPOR RECOVERY

The On-Board Refueling Vapor Recovery (ORVR) system consists of a unique fuel tank, fuel control valve, one-way check valve and vapor canister. (Scheme 50) The ORVR system is used to remove excess fuel tank vapors. This is done while the vehicle is being refueled. Fuel flowing into the fuel filler tube (approx. 1" I.D.) creates an aspiration effect drawing air into the fuel fill tube. During refueling, the fuel tank is vented to the EVAP canister to capture escaping vapors. With air flowing into the filler tube, there are no fuel vapors escaping to the atmosphere. Once the refueling vapors are captured by the EVAP canister, the vehicle's computer controlled purge system draws the vapor out of the canister for the engine to burn. The vapor flow is metered by the purge solenoid so that there is no, or minimal impact on driveability or tailpipe emissions. As fuel starts to flow through the fuel fill tube, it opens the normally closed check valve and enters the fuel tank. Vapor or air is expelled from the tank through the control valve and on to the vapor canister. Vapor is absorbed in the EVAP canister until vapor flow in the lines stops, either following shutoff or by having the fuel level in the tank rise high enough to close the control valve. The control valve contains a float that rises to seal the large diameter vent path to the canister. At this point in the fueling of the vehicle, the tank pressure increases, the check valve closes (preventing tank fuel from spitting back at the operator), and fuel then rises up the filler tube to shutoff the dispensing nozzle.

If the engine is shutoff while the On-Board diagnostics test is running, low level tank pressure can be trapped in the fuel tank and fuel cannot be added to the tank until the pressure is relieved. This is due to the LDP closing the vapor outlet from the top of the tank and the one-way check valve not allowing the tank to vent through the fill tube to atmosphere. Therefore, when fuel is added, it will back-up in the fill tube and shutoff the dispensing nozzle. The pressure can be eliminated in 2 ways: Vehicle purge must be activated for a long enough period to eliminate the pressure or removing the fuel cap and allowing enough time for the system to vent through the recirculation tube.

Scheme 50

PRESSURE RELIEF/ROLLOVER VALVE

The fuel tank is constructed of a plastic material. Its main function is fuel storage and for placement of the fuel pump module. All vehicles pass a 360° rollover without fuel leakage. To accomplish this, fuel and vapor flow controls are required for all fuel tank connections. All models are equipped with either one or two rollover valves mounted into the top of the fuel tank (or pump module). An evaporation control system is connected to the rollover valve(s)/control valve to reduce the emissions of fuel vapors in to the atmosphere, when the tank is vented due to vapor expansion in the tank. When fuel evaporates from the fuel tank, vapors pass through vent hoses or tubes to a charcoal canister where they are temporary held. When the engine is running, the vapors are drawn into the intake manifold. In addition, fuel vapors produced during vehicle refueling are allowed to pass through the vent hose/tubes to the charcoal canister for temporary storage (prior to being drawn into the intake manifold). All models are equipped with a self-diagnosing system using a Leak Detection Pump (LDP) or Natural Vacuum Leak Detection (NVLD).

POSITIVE CRANKCASE VENTILATION

Positive Crankcase Ventilation (PCV) system is used to remove crankcase blow-by gases from crankcase by using a PCV valve and manifold vacuum. Crankcase blow-by gases are drawn through PCV and then returned back into the intake manifold with incoming air/fuel mixture. The PCV valve contains a spring loaded plunger. The plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum. (Scheme 51)and (Scheme 52).

When the engine is not operating, or during an engine backfire, the spring forces the plunger back against the seat. (Scheme 53) This will prevent vapors from flowing through the valve.

During periods of high manifold vacuum, such as idle or cruising speeds, vacuum is sufficient to completely compress the spring. It will then pull the plunger to the top of the valve. (Scheme 54) In this position there is minimal vapor flow through the valve. During periods of moderate manifold vacuum, the plunger is only pulled part way back from inlet. This results in maximum vapor flow through the valve. (Scheme 55)

Scheme 51

Scheme 52

Scheme 53

Scheme 54

Scheme 55

ON-BOARD DIAGNOSTICS

The Powertrain Control Module (PCM) has been programmed to monitor many different circuits of the fuel injection system. This monitoring is called on-board diagnosis. Certain criteria, or arming conditions, must be met for a trouble code to be entered into the PCM memory. The criteria may be a range of engine RPM, engine temperature, and/or input voltage to the PCM. If a problem is sensed with a monitored circuit, and all of the criteria or arming conditions are met, then a trouble code will be stored in the PCM. It is possible that a trouble code for a monitored a circuit may not be entered into the PCM memory even though a malfunction has occurred. This may happen because one of the trouble code criteria have not been met. The PCM compares input signal voltages from each input device with specifications (the established high and low limits of the range) that are programmed into it for that device. If the input voltage is not within specifications and other trouble code criteria are met, a trouble code will be stored in the PCM memory. The On-Board Diagnostics have evolved to the second Generation of Diagnostics referred to as OBD-II/Euro Stage III OBD. These OBD-II/Euro Stage III OBD diagnostics control the functions necessary to meet the requirements of California OBD-II, Federal OBD regulation and European regulation. These requirements specify the inclusion of a Malfunction Indicator Light (MIL). See MALFUNCTION INDICATOR LIGHT . The purpose of the MIL is to inform the vehicle operator in the event of a malfunction of any emission system or component.

If the code applies to a non-emissions related component or system, and the problem is repaired or ceases to exist, the PCM cancels the code after 40 warm-up cycles. Diagnostic trouble codes that affect vehicle emissions illuminate the Malfunction Indicator Lamp (MIL). Refer to Malfunction Indicator Lamp in this section. Certain criteria must be met before the PCM stores a DTC in memory. For example, assume the diagnostic trouble code criteria requires the PCM to monitor the circuit only when the engine operates between 750 and 2000 RPM. Suppose the sensor's output circuit shorts to ground when engine operates above 2400 RPM (resulting in 0 volt input to the PCM). Because the condition happens at an engine speed above the maximum threshold (2000 RPM), the PCM will not store a DTC. There are several operating conditions for which the PCM monitors and sets DTC's.

Note. Various diagnostic procedures may actually cause a diagnostic monitor to set a DTC. For instance, pulling a spark plug wire to perform a spark test may set the misfire code. When a repair is completed and verified, use the DRBIII(R) scan tool to erase all DTC's and extinguish the MIL.

Technicians can display stored DTC's. For obtaining the DTC information, use the Data Link Connector with the DRBIII(R) scan tool.

The Data Link Connector (DLC) is located inside of the vehicle, below instrument panel next to the center column. (Scheme 56) The Powertrain Control Module (PCM) contains a self-diagnostic system which stores a Diagnostic Trouble Code (DTC) if an electronic control system failure exists. DTC may be retrieved from PCM for system diagnosis by using Data Link Connector (DLC) and a scan tool. The DLC also provides a means to communicate with various vehicle control modules, check system operating conditions and to operate various system components. For additional information on using DLC and scan tool usage, see appropriate SELF-DIAGNOSTICS - CARAVAN, TOWN & COUNTRY, & VOYAGER article.

Scheme 56

PCI BUS SYSTEM

Note. For additional information on PCI system communications, see BODY CONTROL MODULES - CARAVAN, TOWN & COUNTRY, & VOYAGER article in ACCESSORIES & EQUIPMENT.

The Programmable Communication Interface Multiplex system (PCI Bus) consist of a single wire. The Body Control Module (BCM) acts as a splice to connect each module and the Data Link Connector (DLC) together. Each module is wired in parallel to the data bus through its PCI chip set and uses its ground as the bus reference. The wiring is a minimum 20 gauge wire. Various modules exchange information through a communications port called the PCI Bus. The Powertrain Control Module (PCM) transmits the Malfunction Indicator Lamp (Check Engine) On/Off signal and engine RPM on the PCI Bus. The PCM receives the Air Conditioning select input, transaxle gear position inputs over the PCI Bus. The PCM also receives the air conditioning evaporator temperature signal from the PCI Bus. The following components access or send information on the PCI Bus

1. Instrument Panel
2. Body Control Module
3. Air Bag System Diagnostic Module
4. Full ATC Display Head (If Equipped)
5. ABS Module
6. Transmission Control Module
7. Powertrain Control Module
8. Travel Module
9. SKIM

STATE DISPLAY TEST MODE

The switch inputs to the Powertrain Control Module (PCM) have two recognized states, HIGH and LOW. For this reason, the PCM cannot recognize the difference between a selected switch position versus an open circuit, a short circuit, or a defective switch. If the State Display screen shows the change from HIGH to LOW or LOW to HIGH, assume the entire switch circuit to the PCM functions properly. Connect the DRBIII(R) scan tool to the data link connector and access the State Display screen. Then access either State Display Inputs and Outputs or State Display Sensors.

TASK MANAGER

The Powertrain Control Module (PCM) is responsible for efficiently coordinating the operation of all the emissions related components. The PCM is also responsible for determining if the diagnostic systems are operating properly. The software designed to carry out these responsibilities is referred to as the "Task Manager". The Task Manager determines which tests happen when and which functions occur when. Many of the diagnostic steps required by OBD-II must be formed under specific operating conditions. The Task Manager software organizes and prioritizes the diagnostic procedures. The job of the Task Manager is to determine if conditions are appropriate for tests to be run, monitor the parameters for a trip for each test, and record the results of the test. The following are the responsibilities of the Task Manager software.

1. Test Sequence
2. MIL Illumination
3. Diagnostic Trouble Codes
4. Trip Indicator
5. Freeze Frame Data Storage
6. Similar Conditions Window

TEST SEQUENCE

In many instances, emissions systems must fail diagnostic tests more than once before the Powertrain Control Module (PCM) illuminates the Malfunction Indicator Light (MIL). These tests are know as "two-trip monitors". Other tests that turn the MIL on after a single failure are known as "one-trip monitors". A trip is defined as start the vehicle and operate it to meet the criteria necessary to run the given monitor. Many of the diagnostic tests must be performed under certain operating conditions. However, there are times when tests cannot be run because another test is in progress (conflict), another test has failed (pending) or the Task Manager has set a fault that may cause a failure of the test (suspend).

1. Pending Under some situations the Task Manager will not run a monitor if the MIL is illuminated and a fault is stored from another monitor. In these situations, the Task Manager postpones monitors pending resolution of the original fault. The Task Manager does not run the test until the problem is remedied. For example, when the MIL is illuminated for an Oxygen Sensor fault, the Task Manager does not run the Catalyst Monitor until the Oxygen Sensor fault is remedied. Since the Catalyst Monitor is based on signals from the Oxygen Sensor, running the test would produce inaccurate results.
2. Conflict There are situations when the Task Manager does not run a test if another monitor is in progress. In these situations, the effects of another monitor running could result in an erroneous failure. If this conflict is present, the monitor is not run until the conflicting condition passes. Most likely the monitor will run later after the conflicting monitor has passed. For example, if the Fuel System Monitor is in progress, the Task Manager does not run the EGR Monitor. Since both tests monitor changes in air/fuel ratio and adaptive fuel compensation, the monitors will conflict with each other.
3. Suspend Occasionally the Task Manager may not allow a two-trip fault to mature. The Task Manager will suspend the maturing of a fault if a condition exists that may induce an erroneous failure. This prevents illuminating the MIL for the wrong fault and allows more precise diagnosis. For example, if the PCM is storing a one-trip fault for the Oxygen Sensor and the EGR monitor, the Task Manager may still run the EGR Monitor but will suspend the results until the Oxygen Sensor Monitor either passes or fails. At that point the Task Manager can determine if the EGR system is actually failing or if an Oxygen Sensor is failing.

The Malfunction Indicator Light (MIL) may also be referred to as the SERVICE ENGINE SOON light. MIL is located in the instrument cluster or the message center (if equipped) on top of driver's side of instrument panel. MIL is displayed as an engine icon. When ignition is first turned on, MIL should come to verify bulb and circuit operation.

The Powertrain Control Module (PCM) Task Manager carries out the illumination of the MIL. The Task Manager triggers MIL illumination upon test failure, depending on monitor failure criteria. The Task Manager Screen shows both a Requested MIL state and an Actual MIL state. When the MIL is illuminated upon completion of a test for a third trip, the Requested MIL state changes to OFF. However, the MIL remains illuminated until the next key cycle. On some vehicles, the MIL will actually turn OFF during the third key cycle. During the key cycle for the third good trip, the Requested MIL state is OFF, while the Actual MIL state is ON. After the next key cycle, the MIL is not illuminated and both MIL states read OFF.

DIAGNOSTIC TROUBLE CODE PRIORITY

With OBD-II, different Diagnostic Trouble Code (DTC) faults have different priorities according to regulations. As a result, the priorities determine MIL illumination and DTC erasure. DTCs are entered according to individual priority. DTCs with a higher priority overwrite lower priority DTCs.

1. Priority 0 This is a non-emissions related DTC.
2. Priority 1 One trip failure of a two-trip DTC for non-fuel system and non-misfire conditions (MIL Off).
3. Priority 2 One trip failure of a two-trip DTC for fuel system rich or fuel system lean condition, or misfire condition (MIL Off).
4. Priority 3 Two trip failure for non-fuel system or non-misfire condition, or a matured one-trip comprehensive component fault (MIL On).
5. Priority 4 Two trip failure or matured fault for fuel system (rich/lean) and misfire or one trip catalyst damaging misfire. Catalyst damage misfire is a 2 trip MIL. The MIL flashes on the first trip when catalyst damage misfire levels are present. (MIL On) Non-emissions related failures have no priority. One trip failures of two trip faults have low priority. Two trip failures or matured faults have higher priority. One and two trip failures of fuel system and misfire monitor take precedence over non-fuel system and non-misfire failures.

Non-emission related failures have no priority. One trip failures of two-trip faults have low priority. Two trip failures or matured faults have higher priority. One and two trip failures of fuel system and misfire monitor take precedence over non-fuel system and non-misfire failures.

DTC SELF-ERASURE

With one-trip components or systems, the MIL is illuminated upon test failure and DTCs are stored. Two-trip monitors are components requiring failure in two consecutive trips for MIL illumination. Upon failure of the first test, the Task Manager enters a maturing code. If the component fails the test for a second time the code matures and a DTC is set. After three good trips, the MIL is extinguished and the Task Manager automatically switches the trip counter to a warm-up cycle counter. DTCs are automatically erased following 40 warm-up cycles if the component does not fail again. For misfire and fuel system monitors, the component must pass the test under a Similar Conditions Window in order to record a good trip. A Similar Conditions Window is when engine RPM is within +/- 375 RPM and load is within +/- 20 percent of when the fault occurred. It is important to understand that a component does not have to fail under a similar window of operation to mature. It must pass the test under a Similar Conditions Window when it failed to record a Good Trip for DTC erasure for misfire and fuel system monitors. DTCs can be erased anytime with a DRBIII(R) scan tool. Erasing the DTC with the DRBIII(R) scan tool erases all OBD-II information. The DRBIII(R) scan tool automatically displays a warning that erasing the DTC will also erase all OBD-II monitor data. This includes all counter information for warm-up cycles, trips and Freeze Frame.

TRIP INDICATOR

The trip is essential for running monitors and turning off the Malfunction Indicator Light (MIL). A trip is defined as a set of vehicle operating conditions that must be met for a specific monitor to run. All trips begin with an ignition key cycle. Good trip counters are: global good trip, fuel system good trip, misfire good trip and alternate good trip (appears as Global Good Trip on DRBIII(R) scan tool).

1. Good Trip The Good Trip counters are as follows, Global Good Trip, Fuel System Good Trip, Misfire Good Trip, Alternate Good Trip (appears as a Global Good Trip on DRBIII(R) scan tool), Comprehensive Components, Major Monitor and Warm-Up Cycles.
2. Global Good Trip To increment a Global Good Trip, the oxygen sensor and catalyst efficiency monitors must have run and passed, and engine run time must be more than 2 minutes.
3. Fuel System Good Trip To count a good trip (3 required) and turn off the MIL, the following conditions must be met. Engine must be in closed loop, must be operating in similar conditions window and short term multiplied by long term must be less than threshold value. For more information on similar conditions window, see «SIMILAR CONDITIONS WINDOW»(/dodge/grand-caravan/iv-2000-2007/remont/theory-operation/#engine-controls-theory-operation__similar-conditions-window) .
4. Misfire Good Trip If operating in similar conditions window and 1000 engine revolutions have occurred with no misfires, the powertrain control module will count one good trip (3 required) in order to turn off MIL.
5. Alternate Good Trip Alternate Good Trips are used in place of Global Good Trips for Comprehensive Components and Major Monitors. If the Task Manager cannot run a Global Good Trip because a component fault is stopping the monitor from running, it will attempt to count an Alternate Good Trip. The Task Manager counts an Alternate Good Trip for Comprehensive components when the following conditions are met: Two minutes of engine run time, idle or driving, and no other faults occur. The Task Manager counts an Alternate Good Trip for a Major Monitor when the monitor runs and passes. Only the Major Monitor that failed needs to pass to count an Alternate Good Trip.
6. Warm-Up Cycles Once the MIL has been turned off by the Good Trip Counter, the Powertrain Control Module (PCM) will automatically switch to a Warm-Up Cycle Counter that can be viewed by the DRBIII(R) scan tool. Warm-up cycles are used to clear DTCs and freeze frame data from PCM memory. Forty warm-up cycles are necessary to clear DTCS and freeze frame data. A warm-up cycle is defined as the engine is started, an increase of 40°F (4°C) in engine coolant temperature exists after engine is started and engine coolant temperature reaches at least 160°F (71°C).

FREEZE FRAME DATA STORAGE

Once a failure occurs, the Task Manager records several engine operating conditions and stores it in a Freeze Frame. The Freeze Frame is considered one frame of information taken by an on-board data recorder. When a fault occurs, the powertrain control module stores the input data from various sensors so that technicians can determine under what vehicle operating conditions the failure occurred. The data stored in Freeze Frame is usually recorded when a system fails the first time for two trip faults. Freeze Frame data will only be overwritten by a different fault with a higher priority. Erasing DTCs, either with the DRBIII(R) scan tool or by disconnecting the battery also clears all Freeze Frame data.

SIMILAR CONDITIONS WINDOW

The similar conditions window displays information about the engine operation during a monitor. Manifold absolute pressure (engine load) and engine RPM information is stored in this window when a failure occurs. There are 2 different similar conditions windows, fuel system and misfire.

Fuel System

1. Fuel System Similar Conditions Window An indicator that ABSOLUTE MAP WHEN FUEL SYS FAIL and RPM WHEN FUEL SYS FAIL are all in the same range when failure occurred. This is indicated by switching from NO to YES.
2. Absolute MAP When Fuel Sys Fail Stored MAP reading at time of failure. Tells at what engine load the failure occurred.
3. Absolute MAP A real-time reading of engine load to aid the user in accessing the Similar Conditions Window.
4. RPM When Fuel Sys Fail Stores the engine RPM at time of failure. Informs the user at what engine RPM the failure occurred.
5. Engine RPM A real-time reading of engine RPM to aid the user in accessing the Similar Conditions Window.
6. Adaptive Memory Factor The powertrain control module uses both Short Term Compensation and Long Term Adaptive to calculate Adaptive Memory Factor for total fuel correction.
7. Upstream O2S Volts A real-time reading of O2 sensor to indicate performance of sensor. For example, stuck lean, stuck rich, etc.
8. Similar Conditions Window (SCW) Time In Window The powertrain control module uses this timer to indicate that after all Similar Conditions have been met, if engine has been running good enough in SCW without failure detected. This timer is used to increment a Good Trip.
9. Fuel System Good Trip Counter This trip counter is used to turn off the MIL for fuel system DTCs. A Fuel System Good Trip increment is when engine is in Similar Conditions Window, Adaptive Memory Factor must be less than calibrated threshold and Adaptive Memory Factor must stay below that threshold for a specific amount of time.
10. Test Done This Trip Indicates the monitor has already run and completed during the current trip.

Misfire

1. Same Misfire Warm-Up State Indicates if misfire occurred when engine was warmed-up more than 160°F (71°C).
2. In Similar Misfire Window Indicates that Absolute MAP When Misfire Occurred and RPM When Misfire Occurred are all in the same range when failure occurred. Indicated by switching from NO to YES.
3. Absolute MAP When Misfire Occurred Stored MAP reading at time of failure. Tells what engine load the failure occurred.
4. Absolute MAP A real-time reading of engine load to aid the user in accessing the Similar Conditions Window.
5. RPM When Misfire Occurred Stores the engine RPM at time of failure.
6. Engine RPM A real-time reading of engine RPM to aid the user in accessing the Similar Conditions Window.
7. Adaptive Memory Factor The powertrain control module uses both Short Term Compensation and Long Term Adaptive to calculate Adaptive Memory Factor for total fuel correction.
8. 200 Rev Counter Counts 0-100 720° cycles.
9. Similar Conditions Window (SCW) Cat 200 Rev Counter Counts when in Similar Conditions.
10. Similar Conditions Window (SCW) FTP 1000 Rev Counter Counts 0-4 when in Similar Conditions.
11. Misfire Good Trip Counter Counts up to 3 to turn off MIL.

MONITORS

There are electronic circuit monitors that check fuel, emission, engine and ignition performance. These monitors use information from various sensor circuits to indicate the overall operation of the fuel, engine, ignition and emission systems and thus the emissions performance of the vehicle. The fuel, engine, ignition and emission systems monitors do not indicate a specific component problem. They do indicate that there is an implied problem within one of the systems and that a specific problem must be diagnosed. If any of these monitors detect a problem affecting vehicle emissions, the Malfunction Indicator Light (MIL) will be illuminated. These monitors generate Diagnostic Trouble Codes that can be displayed with the MIL or a scan tool. The following is a list of the system monitors

1. EGR Monitor (If Equipped)
2. Misfire Monitor
3. Fuel System Monitor
4. Oxygen Sensor Monitor
5. Oxygen Sensor Heater Monitor
6. Catalyst Monitor
7. Leak Detection Pump Monitor

All these system monitors require two consecutive trips with the malfunction present to set a fault. For diagnostic procedures, see appropriate SELF-DIAGNOSTICS article.

Misfire Monitor

Excessive engine misfire results in increased catalyst temperature and causes an increase in HC emissions. Severe misfires could cause catalyst damage. To prevent catalytic converter damage, the Powertrain Control Module (PCM) monitors engine misfire. The PCM monitors for misfire during most engine operating conditions (positive torque) by looking at changes in the crankshaft speed. If a misfire occurs, the speed of the crankshaft will vary more than normal.

Fuel System Monitor

To comply with clean air regulations, vehicles are equipped with a catalytic converters. These converters reduce the emission of hydrocarbons, oxides of nitrogen and carbon monoxide. The catalyst works best when the air/fuel ratio is at or near the optimum of 14.7 to 1. The Powertrain Control Module (PCM) is programmed to maintain the optimum air/fuel ratio of 14.7 to 1. This is done by making short term corrections in the fuel injector pulse width based on the Oxygen (O2) sensor output. The programmed memory acts as a self calibration tool that the engine controller uses to compensate for variations in engine specifications, sensor tolerances and engine fatigue over the life span of the engine. By monitoring the actual air/fuel ratio with the O2 sensor (short term) and multiplying that with the program long-term (adaptive) memory and comparing that to the limit, it can be determined whether it will pass an emissions test. If a malfunction occurs such that the PCM cannot maintain the optimum air/fuel ratio, then the MIL will be illuminated.

Oxygen Sensor Monitor

Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the Oxygen (O2) sensor. The O2 sensor is located in the exhaust path. Once it reaches operating temperature 572-662°F (300-350°C), the sensor generates a voltage that is inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse width. This maintains a 14.7 to 1 air/fuel ratio. At this mixture ratio, the catalyst works best to remove Hydrocarbons (HC), Carbon Monoxide (CO) and Nitrogen Oxide (NOx) from the exhaust.

The O2 sensor is also the main sensing element for the EGR (If Equipped), Catalyst and Fuel Monitors. The O2 sensor can fail in any or all of the following manners.

1. Slow Response Rate
2. Reduced Output Voltage
3. Dynamic Shift
4. Shorted Or Open Circuits

Response rate is the time required for the sensor to switch from lean to rich once it is exposed to a richer than optimum air/fuel mixture or vice versa. As the sensor starts malfunctioning, it could take longer to detect the changes in the oxygen content of the exhaust gas. The output voltage of the O2 sensor ranges from 0 to 1 volt (voltages are offset by 2.5 volts on the NGC vehicles). A good sensor can easily generate any output voltage in this range as it is exposed to different concentrations of oxygen. To detect a shift in the air/fuel mixture (lean or rich), the output voltage has to change beyond a threshold value. A malfunctioning sensor could have difficulty changing beyond the threshold value.

Oxygen Sensor Heater Monitor

If there is an Oxygen (O2) sensor shorted to voltage DTC, as well as a O2 sensor heater DTC, the O2 sensor fault must be repaired first. Before checking the O2 sensor fault, verify that the heater circuit is operating correctly. Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the O2 sensor. The O2 sensor is located in the exhaust path. Once it reaches operating temperature 572-662°F (300-350°C), the sensor generates a voltage that is inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse width. This maintains a 14.7 to 1 air/fuel ratio. At this mixture ratio, the catalyst works best to remove Hydrocarbons (HC), Carbon Monoxide (CO) and Nitrogen Oxide (NOx) from the exhaust. The voltage readings taken from the O2 sensor are very temperature sensitive. The readings are not accurate below 572°F (300°C). Heating of the O2 sensor is done to allow the engine controller to shift to closed loop control as soon as possible. The heating element used to heat the O2 sensor must be tested to ensure that it is heating the sensor properly. The O2 sensor circuit is monitored for a drop in voltage. The sensor output is used to test the heater by isolating the effect of the heater element on the O2 sensor output voltage from the other effects.

Catalyst Monitor

To comply with clean air regulations, vehicles are equipped with catalytic converters. These converters reduce the emission of Hydrocarbons (HC), Carbon Monoxide (CO) and Nitrogen Oxide (NOx). Normal vehicle miles or engine misfire can cause a catalyst to decay. This can increase vehicle emissions and deteriorate engine performance, driveability and fuel economy. The catalyst monitor uses dual Oxygen (O2) sensors to monitor the efficiency of the converter. The dual O2 sensor's strategy is based on the fact that as a catalyst deteriorates, its oxygen storage capacity and its efficiency are both reduced. By monitoring the oxygen storage capacity of a catalyst, its efficiency can be indirectly calculated. The upstream O2 sensor is used to detect the amount of oxygen in the exhaust gas before the gas enters the catalytic converter. The Powertrain Control Module (PCM) calculates the air/fuel mixture from the output of the O2 sensor. A low voltage indicates high oxygen content (lean mixture). A high voltage indicates a low content of oxygen (rich mixture). When the upstream O2 sensor detects a lean condition, there is an abundance of oxygen in the exhaust gas. A functioning converter would store this oxygen so it can use it for the oxidation of HC and CO. As the converter absorbs the oxygen, there will be a lack of oxygen downstream of the converter. The output of the downstream O2 sensor will indicate limited activity in this condition. As the converter loses the ability to store oxygen, the condition can be detected from the behavior of the downstream O2 sensor. When the efficiency drops, no chemical reaction takes place. This means the concentration of oxygen will be the same downstream as upstream. The output voltage of the downstream O2 sensor copies the voltage of the upstream sensor. The only difference is a time lag (seen by the PCM) between the switching of the O2 sensor's. To monitor the system, the number of lean-to-rich switches of upstream and downstream O2 sensor's is counted. The ratio of downstream switches to upstream switches is used to determine whether the catalyst is operating properly. An effective catalyst will have fewer downstream switches than it has upstream switches i.e., a ratio closer to zero. For a totally ineffective catalyst, this ratio will be one-to-one, indicating that no oxidation occurs in the device. The system must be monitored so that when catalyst efficiency deteriorates and exhaust emissions increase to over the legal limit, the MIL will be illuminated.

NON-MONITORED CIRCUITS

The Powertrain Control Module (PCM) does not monitor all circuits, systems and conditions that could have malfunctions causing driveability problems. However, problems with these systems may cause the PCM to store Diagnostic Trouble Codes (DTC) for other systems or components. For example, a fuel pressure problem will not register a fault directly, but could cause a rich/lean condition or misfire. This could cause the PCM to store an oxygen sensor or misfire diagnostic trouble code. The major non-monitored circuits are listed below along with examples of failures modes that do not directly cause the PCM to set a DTC, but for a system that is monitored.

1. Cylinder Compression The PCM cannot detect uneven, low or high cylinder compression. Low compression lowers oxygen content in the exhaust which leads to fuel system, oxygen sensor or misfire detection fault.
2. Engine Timing The PCM cannot detect an incorrectly indexed timing chain, camshaft sprocket, or crankshaft sprocket.
3. Excessive Oil Consumption Although the PCM monitors engine exhaust oxygen content when the system is in closed loop, it cannot determine excessive oil consumption.
4. Exhaust System The PCM cannot detect a plugged, restricted or leaking exhaust system, although it may set a diagnostic trouble code for EGR, oxygen sensor or fuel system fault.
5. Fuel Injector Mechanical Malfunctions The PCM cannot determine if a fuel injector is clogged, needle is sticking or if the wrong injector is installed. However, these could result in a rich or lean condition causing the PCM to store a diagnostic trouble code for a misfire, oxygen sensor or fuel system.
6. Fuel Pressure The fuel pressure regulator controls fuel system pressure. The PCM cannot detect a clogged fuel pump inlet filter, clogged in-line fuel filter, or a pinched fuel supply. However, these could result in a rich or lean condition causing the PCM to store an oxygen sensor, or fuel system diagnostic trouble code.
7. Fuel Requirements Poor quality gasoline can cause problems such as hard starting, stalling, and stumble. Use of methanol-gasoline blends may result in starting and driveability problems.
8. PCM Connector Engagement The PCM may not be able to determine spread or damaged connector pins. However, it might store diagnostic trouble codes as a result of spread connector pins.
9. PCM System Ground The PCM cannot determine a poor system ground. However, one or more diagnostic trouble codes may be generated as a result of this condition. The module should be mounted to the body at all times, also during diagnostics.
10. Secondary Ignition Circuit The PCM cannot detect an inoperative ignition coil, fouled or worn spark plugs, ignition cross firing or open spark plug cables. The misfire will however, increase the oxygen content in the exhaust, deceiving the PCM into thinking the fuel system is too lean.
11. Throttle Body Airflow The PCM cannot detect a clogged or restricted air cleaner inlet or filter element.
12. Vacuum Assist The PCM cannot detect leaks or restrictions in the vacuum circuits of vacuum assisted engine control system devices. However, these could cause the PCM to store a MAP sensor diagnostic trouble code and cause a high idle condition.

HIGH & LOW LIMITS

The Powertrain Control Module (PCM) compares input signal voltages from each input device with established high and low limits for the device. If the input voltage is not within limits and other criteria are met, the PCM stores a diagnostic trouble code in memory. Other diagnostic trouble code criteria might include engine RPM limits or input voltages from other sensors or switches that must be present before verifying a diagnostic trouble.

TRIP DEFINITION

A "Trip" means vehicle operation (following an engine-off period) of duration and driving mode such that all components and systems are monitored at least once by the diagnostic system. The monitors must successfully pass before the Powertrain Control Module (PCM) can verify that a previously malfunctioning component is meeting the normal operating conditions of that component. For misfire or fuel system malfunction, the MIL may be extinguished if the fault does not recur when monitored during 3 subsequent sequential driving cycles in which conditions are similar to those under which the malfunction was first determined. Anytime the MIL is illuminated, a DTC is stored. The DTC can self erase only after the MIL has been extinguished. Once the MIL is extinguished, the PCM must pass the diagnostic test for the most recent DTC for 40 warm-up cycles (80 warm-up cycles for the Fuel System Monitor and the Misfire Monitor). A warm-up cycle can best be described by the following

1. The engine must be running.
2. A rise of 40°F (4.4°C) in engine temperature must occur from the time when the engine was started.
3. Engine coolant temperature must increase to more than 160°F (71°C).
4. A "driving cycle" that consists of engine start-up and engine shutoff.

Once the above conditions occur, the PCM is considered to have passed a warm-up cycle. Due to the conditions required to extinguish the MIL and erase the DTC, it is most important that after a repair has been made, all DTCs be erased and the repair verified by running 1-good trip.

MISCELLANEOUS CONTROLS

Note. Although not considered true engine performance related systems, some controlled devices may affect driveability if they malfunction.

ENGINE BLOCK HEATER

The engine block heater is available as an optional accessory on all models. The heater is operated by ordinary house current (110 Volt AC) through a power cord located behind the radiator grille. This provides easier engine starting and faster warm-up when vehicle is operated in areas having extremely low temperatures. The heater is mounted in a core hole (in place of a core hole plug) in the engine block, with the heating element immersed in coolant. The block heater element is submerged in the cooling system's coolant. When electrical power (110 volt AC) is applied to the element, it creates heat. This heat is transferred to the engine coolant. This provides easier engine starting and faster warm-up when vehicle is operated in areas having extremely low temperatures.

The compressor clutch relay is a International Standards Organization (ISO) micro-relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The ISO micro-relay terminal functions are the same as a conventional ISO relay. However, the ISO micro-relay terminal pattern (or footprint) is different, the current capacity is lower, and the physical dimensions are smaller than those of the conventional ISO relay. The compressor clutch relay is located in the Intelligent Power Module (IPM), which is in the engine compartment near the battery. See the fuse and relay layout map molded into the inner surface of the IPM cover for compressor clutch relay identification and location.

The Black, molded plastic case is the most visible component of the compressor clutch relay. Five male spade-type terminals extend from the bottom of the base to connect the relay to the vehicle electrical system, and the ISO designation for each terminal is molded into the base adjacent to each terminal.

The compressor clutch relay is an electromechanical switch that uses a low current input from the Powertrain Control Module (PCM) to control the high current output to the compressor clutch electromagnetic coil. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws, the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. The resistor or diode is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The compressor clutch relay terminals are connected to the vehicle electrical system through a receptacle in the Intelligent Power Module (IPM). The inputs and outputs of the compressor clutch relay include

Note. For illustration of relay (Scheme 57) The numbers in parenthesis in the following list refer to numbers in illustration.

1. The common feed terminal (30) receives a battery current input from a fuse in the IPM through a fused B(+) circuit at all times.
2. The coil ground terminal (85) receives a ground input from the PCM through the compressor clutch relay control circuit only when the PCM electronically pulls the control circuit to ground.
3. The coil battery terminal (86) receives a battery current input from the PCM through a fused ignition switch output (run-start) circuit only when the ignition switch is in the On or Start positions.
4. The normally open terminal (87) provides a battery current output to the compressor clutch coil through the compressor clutch relay output circuit only when the compressor clutch relay coil is energized.
5. The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the compressor clutch relay coil is de-energized.

Scheme 57

The relay is located in the Power Distribution Center (PDC). For the location of the relay within the PDC, refer to the PDC cover for location. (Scheme 1)

The ASD sense circuit (SBEC vehicles) or the engine switched battery (NGC vehicles) informs the Powertrain Control Module (PCM) when the ASD relay energizes. A 12-volt signal at this input indicates to the PCM that the ASD has been activated. This input is also used to power certain drivers on NGC vehicles. When energized, the ASD relay on SBEC vehicles supplies battery voltage to the fuel injectors, ignition coils and the heating element in each oxygen sensor. When energized, the ASD relay on NGC vehicles provides power to operate the injectors, ignition coil, generator field, O2 sensor heaters (both upstream and downstream), evaporative purge solenoid, EGR solenoid (if equipped) wastegate solenoid (if equipped), and NVLD solenoid (if equipped). For both SBEC and NGC vehicles, the ASD relay also provides a sense circuit to the PCM for diagnostic purposes. If the PCM does not receive 12 volts from this input after grounding the control side of the ASD relay, it sets a Diagnostic Trouble Code (DTC). The PCM energizes the ASD any time there is an, engine speed that exceeds a predetermined value (typically about 50 RPM). The ASD relay can also be energized after the engine has been turned off to perform an O2 sensor heater test. As mentioned earlier, the PCM energizes the ASD relay during an O2 sensor heater test. This test is performed only after the engine has been shut off for SBEC vehicles. On NGC vehicles it checks the O2 heater upon vehicle start. The PCM still operates internally to perform several checks, including monitoring the O2 sensor heaters.

Radiator Fan Relay

The radiator fan relay is a solid state type and is located on the front bumper reinforcement. (Scheme 58) The solid state radiator fan relay is controlled by the Powertrain Control Module (PCM) by way of a Pulse Width Modulated (PWM) signal. The relay control circuit supplies a 12-volt signal to the PCM. The PCM then pulses the ground circuit to achieve fan on time. The relay provides a voltage to the fan motors which is proportional to the pulse width it receives from the PCM. The duty cycle ranges from 30% for low speed operation, then ramps-up to 100% for high speed operation. This fan control system provides infinitely variable fan speeds, allowing for improved fan noise, A/C performance, better engine cooling, and additional vehicle power. To control operation of the relay, the PCM looks at inputs from

1. Engine Coolant Temperature
2. A/C Pressure Transducer
3. Ambient Temperature From The Body Controller
4. Vehicle Speed
5. Transmission Oil Temperature

The PCM uses these inputs to determine when the fan should operate and at what speed.

Scheme 58

Starter relay is located in the Power Distribution Center (PDC) in engine compartment. Starter relay provides battery voltage to solenoid on starter motor for starter operation. A double-start override feature is used on the starting system to prevent starter from operating if engine is already running.

When ignition switch is in START position, starter relay receives voltage at the other side of the relay from ignition switch. The Powertrain Control Module (PCM) provides the ground circuit to energize starter relay. When starter relay is energized, PCM monitors engine RPM and will remove the ground circuit once engine RPM has reached a predetermined RPM. This prevents starter from operating if engine is already running.

GENERATOR

The Powertrain Control Module (PCM) uses various input signals and an internal electronic voltage regulator to maintain charging system voltage at 12.9-15.0 volts. Internal electronic voltage regulator controls charging system voltage by cycling the ground circuit on the generator field. Battery voltage is supplied to generator through a fusible link and the Auto Shutdown (ASD) relay. For operation of ASD relay, see AUTO SHUTDOWN RELAY . If a failure exists in the charging system, a diagnostic trouble code will be stored in the PCM. For additional charging system information, see GENERATORS & REGULATORS - CARAVAN, TOWN & COUNTRY, & VOYAGER article in ELECTRICAL.

The generator is belt-driven by the engine. The generator produces DC voltage at the B+ terminal. If the generator is failed, the generator assembly sub-components (generator and decoupler pulley) must be inspected for individual failure and replaced accordingly. As the energized rotor begins to rotate within the generator, the spinning magnetic field induces a current into the windings of the stator coil. Once the generator begins producing sufficient current, it also provides the current needed to energize the rotor. The Y-type stator winding connections deliver the induced AC current to 3 positive and 3 negative diodes for rectification. From the diodes, rectified DC current is delivered to the vehicles electrical system through the generator, battery, and ground terminals. Excessive or abnormal noise emitting from the generator may be caused by

1. Worn, Loose Or Defective Bearings
2. Loose Or Defective Drive Pulley (2.4L) Or Decoupler (3.3L & 3.8L)
3. Incorrect, Worn, Damaged Or Misadjusted Drive Belt
4. Loose Mounting Bolts
5. Misaligned Drive Pulley
6. Defective Stator Or Diode
7. Damaged Internal Fins

CRUISE CONTROL SYSTEM

The speed control system is electronically controlled and vacuum operated. The electronic control is integrated into the Powertrain Control Module (PCM). The controls are located on the steering wheel. The On/Off, and Set buttons are located on the left side of the air bag module. The Resume/Accel, Cancel and Coast buttons are located on the right side of the air bag module. The system is designed to operate at speeds above 30 MPH. When speed control is activated by depressing the On switch, the PCM allows a set speed to be stored in RAM for speed control. To store a set speed, depress and release the SET switch while the vehicle is moving at a speed between 30 and 85 MPH. In order for the speed control to engage, the brakes cannot be applied, nor can the gear selector be indicating the transmission is in Park or Neutral. The speed control can be disengaged manually by stepping on the brake pedal, depressing the Off switch, depressing the Cancel switch, depressing the clutch pedal or operating in 1st or 2nd gear (autostick, if equipped).

For added safety, the speed control system is programmed to disengage for any of the following conditions

1. An indication of Park or Neutral.
2. A rapid increase RPM (indicates that the clutch has been disengaged).
3. Excessive engine RPM (indicates that the transmission may be in a low gear).
4. The speed signal increases at a rate of 10 MPH per second (indicates that the co-efficient of friction between the road surface and tires is extremely low).
5. The speed signal decreases at a rate of 10 MPH per second (indicates that the vehicle may have decelerated at an extremely high rate).
6. If the actual speed is greater than 20 MPH over the set speed.
7. Autostick shifts into 1st or 2nd gear (autostick, if equipped).

Once the speed control has been disengaged, depressing the Resume switch when speed is greater than 20 MPH allows the vehicle to resume control to the target speed that was stored in the PCM. While the speed control is engaged, the driver can increase the vehicle speed by depressing the Accel switch. The new target speed is stored in the PCM when the Accel switch is released. The PCM also has a "tap-up" feature in which target speed increases by 2 MPH for each momentary switch activation of the Accel switch. The PCM also provides a means to decelerate to a new lower target speed without disengaging speed control. Depress and hold the Coast switch until the desired speed is reached, then release the switch. The PCM also has a "Tap Down" feature in which target speed decreases at 1 MPH for each momentary switch activation of the coast switch.

The powertrain control module supplies engine RPM to tachometer on instrument panel through the PCI Bus.

The powertrain control module and Transmission Control Module (TCM) supply various information between each other through the PCI bus. This information includes engine speed and vehicle load, and is used for operating the transmission and electronic engine controls. The TCM is located behind left front fender and is mounted to frame rail. (Scheme 59)

The TCM is the controlling unit for all electronic operations of the transaxle. The TCM receives information regarding vehicle operation from both direct and indirect inputs, and selects the operational mode of the transaxle. Direct inputs are hard-wired to, and used specifically by the TCM. Indirect inputs originate from other components/modules, and are shared with the TCM via the J1850 communication bus.

Some examples of direct inputs to the TCM are

1. Battery (B+) Voltage
2. Ignition "ON" Voltage
3. Transmission Control Relay (Switched B+)
4. Throttle Position Sensor
5. Crankshaft Position Sensor (CKP)
6. Transmission Range Sensor (TRS)
7. Pressure Switches (L/R, 2/4, OD)
8. Transmission Temperature Sensor (Integral To TRS )
9. Input Shaft Speed Sensor
10. Output Shaft Speed Sensor

Some examples of indirect inputs to, the TCM are

1. Engine/Body Identification
2. Manifold Pressure
3. Target Idle
4. Torque Reduction Confirmation
5. Speed Control ON/OFF Switch
6. Engine Coolant Temperature
7. Ambient/Battery Temperature
8. Brake Switch Status
9. DRBIII(R) Scan Tool Communication

Based on the information received from these various inputs, the TCM determines the appropriate shift schedule and shift points, depending on the present operating conditions and driver demand. This is possible through the control of various direct and indirect outputs.

Some examples of TCM direct outputs are

1. Transmission Control Relay
2. Solenoids (LR/CC, 2/4, OD & UD)
3. Vehicle Speed (To PCM)
4. Torque Reduction Request (To PCM)

An example of a TCM indirect output is

1. Transmission Temperature (To PCM)

In addition to monitoring inputs and controlling outputs, the TCM has other important responsibilities and functions

1. Storing & Maintaining Clutch Volume Indexes (CVI)
2. Storing & Selecting Appropriate Shift Schedules
3. System Self-Diagnostics
4. Diagnostic Capabilities (With DRBIII(R) Scan Tool)

Scheme 59

CARAVAN

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

GRAND CARAVAN

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

TOWN & COUNTRY

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

VOYAGER

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

See also:
• SELF-DIAGNOSTIC SYSTEM
• INPUT DEVICES
• OUTPUT SIGNALS
• PARK/NEUTRAL SWITCH (TRANSMISSION RANGE SENSOR)
• EXHAUST GAS RECIRCULATION SYSTEM
• EVAPORATIVE EMISSIONS SYSTEM
• GENERATOR
• LEAK DETECTION PUMP SYSTEM
• RADIATOR FAN CONTROL RELAY
• EVAP CANISTER
• EVAP CANISTER PURGE SOLENOID
• NATURAL VACUUM LEAK DETECTION (2.4L)
• ON-BOARD REFUELING VAPOR RECOVERY
• SIMILAR CONDITIONS WINDOW