Electronic Control Modules - Service Information: Overview Dodge Dakota III рестайлинг

DESCRIPTION

The primary on-board communication network between microprocessor-based electronic control modules in this vehicle is the Controller Area Network (CAN) data bus system. A data bus network minimizes redundant wiring connections; and, at the same time, reduces wire harness complexity, sensor current loads and controller hardware by allowing each sensing device to be connected to only one module (also referred to as a node). Each node reads, then broadcasts its sensor data over the bus for use by all other nodes requiring that data. Each node ignores the messages on the bus that it cannot use.

The CAN bus is a two-wire multiplex system. Multiplexing is any system that enables the transmission of multiple messages over a single channel or circuit. The CAN bus is used for communication between all vehicle nodes. However, in addition to the CAN bus network, certain nodes may also be equipped with a dedicated Serial Controller Interface (SCI) or a K-Line serial link bus to provide direct communication between that node and certain sensor inputs.

There are actually three separate CAN bus systems used in the vehicle. They are designated: the CAN-B, the CAN-C and the Diagnostic CAN-C. The CAN-B and CAN-C systems provide on-board communication between all of the nodes that are connected to them. The CAN-C is the faster of the two systems providing near real-time communication (500 Kbps), but is less fault tolerant than the CAN-B system. The CAN-C is used typically for communications between more critical nodes, while the slower (83.3 Kbps), but more fault tolerant CAN-B system is used for communications between less critical nodes. The CAN-B fault tolerance comes from its ability to revert to a single wire communication mode if there is a fault in the bus wiring.

The added speed of the CAN data bus network is many times faster than previous data bus systems. This added speed facilitates the addition of more electronic control modules or nodes and the incorporation of many new electrical and electronic features in the vehicle.

The Diagnostic CAN-C bus is also capable of 500 Kbps communication, and is sometimes informally referred to as the CAN-D system to differentiate it from the other high speed CAN-C bus. The Diagnostic CAN-C is used exclusively for the transmission of diagnostic information between the Front Control Module (FCM) and a diagnostic scan tool connected to the industry-standard 16-way Data Link Connector (DLC) located beneath the instrument panel on the driver side of the vehicle.

All vehicles have a Central GateWay (CGW or FCMCGW) or hub module integral to the FCM that is connected to all three CAN buses. This gateway physically and electrically isolates the CAN buses from each other and coordinates the bi-directional transfer of messages between them.

OPERATION

The Controller Area Network (CAN) data bus allows all electronic modules or nodes connected to the bus to share information with each other. Regardless of whether a message originates from a module on the lower speed CAN-B bus or on the higher speed CAN-C or CAN-D bus, the message structure and layout is similar, which allows the Front Control Module/Central GateWay (FCM or FCMCGW) to process and transfer messages between the buses. The FCM also stores a Diagnostic Trouble Code (DTC) for certain bus network faults.

All modules (also referred to as nodes) transmit and receive messages over one of these buses. Data exchange between nodes is achieved by serial transmission of encoded data messages. Each node can both send and receive serial data simultaneously. Each digital bit of a CAN bus messages is carried over the bus as a voltage differential between the two bus circuits which, when strung together, form a message. Each node uses arbitration to sort the message priority if two competing messages are attempting to be broadcast at the same time.

The voltage network used to transmit messages requires biasing and termination. Each module on the CAN bus network provides its own biasing and termination. There are two types of nodes used in the CAN bus network. On the CAN-C bus, a dominant node has a 120 ohm termination resistance while a non-dominant (or recessive) node has about a 2500 to 3000 ohm (2.5 to 3.0 kilohm) termination resistance. The dominant nodes on the CAN-C bus are the FCM and the Powertrain Control Module (PCM).

The termination resistance of two dominant nodes is combined in parallel to provide a total of about 60 ohms. This resistance value may vary somewhat by application, depending upon the number of non-dominant nodes on the CAN-C bus. On the CAN-D bus (or Diagnostic CAN-C) all of the 60 ohm termination resistance is present in the Central GateWay (FCMCGW).

Note. All measurement of termination resistance is done with the vehicle battery disconnected.

Note. Termination resistance of a CAN-B node cannot be verified with a Digital Multi-Meter (DMM) or Digital Volt-Ohm Meter (DVOM). The transceiver of each CAN-B node connects to termination resistors internally. When the vehicle battery is disconnected, the internal connections of all CAN-B node transceivers are switched open, disconnecting the termination resistors. Therefore, the total bus resistance measured under these conditions will be extremely high or infinite, which does not accurately reflect the actual termination resistance of the CAN-B bus.

The communication protocol being used for the CAN data bus is a non-proprietary, open standard adopted from the Bosch CAN Specification 2.0b. The CAN-C is the faster of the two primary buses in the CAN bus system, providing near real-time communication (500 Kbps).

The CAN bus nodes are connected in parallel to the two-wire bus using a twisted pair, where the wires are wrapped around each other to provide shielding from unwanted electromagnetic induction, thus preventing interference with the relatively low voltage signals being carried through them. The twisted pairs have between 33 and 50 twists per meter (yard). While the CAN bus is operating (active), one of the bus wires will carry a higher voltage and is referred to as the CAN High or CAN bus (+) wire, while the other bus wire will carry a lower voltage and is referred to as the CAN Low or CAN bus (-) wire. Refer to the CAN BUS VOLTAGES chart below.

In order to minimize the potential effects of Ignition-OFF Draw (IOD), the CAN-B network employs a sleep strategy. However, a network sleep strategy should not be confused with the sleep strategy of the individual nodes on that network, as they may differ. For example: The CAN-C bus network is awake only when the ignition switch is in the ON or START positions; however, the FCM, which is on the CAN-C bus, may still be awake with the ignition switch in the ACCESSORY or UNLOCK positions. The integrated circuitry of an individual node may be capable of processing certain sensor inputs and outputs without the need to utilize network resources.

The CAN-B bus network remains active until all nodes on that network are ready for sleep. This is determined by the network using tokens in a manner similar to polling. When the last node that is active on the network is ready for sleep, and it has already received a token indicating that all other nodes on the bus are ready for sleep, it broadcasts a bus sleep acknowledgment message that causes the network to sleep. Once the CAN-B bus network is asleep, any node on the bus can awaken it by transmitting a message on the network. The FCM will keep either the CAN-B or the CAN-C bus awake for a timed interval after it receives a diagnostic message for that bus over the Diagnostic CAN-C bus.

In the CAN system, available options are configured into the FCM at the assembly plant, but additional options can be added in the field using the diagnostic scan tool. The configuration settings are stored in non-volatile memory. The FCM also has two 64-bit registers, which track each of the as-built and currently responding nodes on the CAN-B and CAN-C buses. The FCM stores a Diagnostic Trouble Code (DTC) in one of two caches for any detected active or stored faults in the order in which they occur. One cache stores powertrain (P-Code), chassis (C-Code) and body (B-Code) DTCs, while the second cache is dedicated to storing network (U-Code) DTCs.

If there are intermittent or active faults in the CAN network, a diagnostic scan tool connected to the Diagnostic CAN-C bus through the 16-way Data Link Connector (DLC) may only be able to communicate with the FCM. To aid in CAN network diagnosis, the FCM will provide CAN-B and CAN-C network status information to the scan tool using certain diagnostic signals. In addition, the transceiver in each node on the CAN-C bus will identify a bus off hardware failure , while the transceiver in each node on the CAN-B bus will identify a general bus hardware failure . The transceivers for some CAN-B nodes will also identify certain failures for both CAN-B bus signal wires.

Scheme 38

The Data Link Connector (DLC) (2) is a 16-way molded plastic connector insulator on a dedicated take out of the instrument panel wire harness. This connector is located at the lower edge of the instrument panel, outboard of the steering column. The connector insulator is retained by integral snap features within a rectangular cutout in the stamped metal lower instrument panel reinforcement, just below the lower edge of the instrument panel steering column opening cover and inboard of the park brake release (1) and inside hood release (3) handles.

The Data Link Connector (DLC) is an industry-standard 16-way connector that permits the connection of a diagnostic scan tool to the Controller Area Network (CAN) data bus for interfacing with, configuring, and retrieving Diagnostic Trouble Code (DTC) data from the electronic modules that reside on the data bus network of the vehicle.

The Antilock Brake Module (ABM) is a microprocessor which handles testing, monitoring and controlling the ABS brake system operation.

The ABM is mounted on the top of the hydraulic control unit (HCU). The ABM operates the ABS system and is separate from other vehicle electrical circuits. ABM voltage source is through CKT A111 (fused B+).

Note. If the ABM needs to be replaced, the rear axle type and tire revolutions per mile must be programed into the new ABM. For axle type refer to DIFFERENTIAL AND DRIVELINE . For tire revolutions per mile. Refer to Tires and Wheels/Tires - Specifications . To program the ABM refer to the appropriate Diagnostic Service Information.

As messages are sent over the Controller Area Network (CAN) bus circuit, the Front Control Module (FCM) reads these messages and controls power to some of the vehicles electrical systems by completing the circuit to ground (low side driver) or completing the circuit to 12 volt power (high side driver). The following functions are controlled by the FCM

1. Front turn signals
2. Stop, turn signal and tail lamps
3. Front and rear hazard warning lamps
4. Headlamps
5. Fog Lamps
6. Daytime running lamps - if equipped
7. Horn
8. Windshield and liftgate wiper and washer systems
9. Transfer case shifting
10. Trailer tow wiring output
11. Rear window defroster power and timing

The FCM provides the following features for the above function

1. It operates the electric transfer case mechanism, replacing a stand-alone module.
2. It flashes lamps in response to turn signal, Remote Keyless Entry and Vehicle Theft Security Alarm inputs.
3. It sounds the horn in response to Remote Keyless Entry and Vehicle Theft Security Alarm inputs.
4. It turns off the horn in the event of excessively long operation that could otherwise damage the horn.
5. It minimized voltage variations to the headlamps to extend bulb life and to equalize the light output from the lamps, which might otherwise differ due to variations in wiring resistance.
6. If the headlamps are left on, it automatically turns them off after eight minutes to protect the battery from discharge.
7. It monitors battery voltage and turns off non-essential functions such as the fog lamps, rear window defogger and heated seats if necessary to conserve battery power.
8. It operates the high-beam headlamps at reduced intensity by pulse-width modulation of the power supply to provide the daytime running lamps.
9. It provides the variable delay intermittent windshield and liftgate wiper time delay features, and the vehicle speed sensitive windshield wiper delay variation.
10. It acts as a gateway between the CAN-C network for critical powertrain and anti-lock brake systems and the CAN-B network for body and interior modules. For example it collects battery temperature data and relays it to the PCM.

Scheme 39

1. Disconnect and isolate the negative battery cable.
2. Remove the Integrated Power Module (IPM) from the engine compartment. Refer to «Electrical - Wiring/Power Distribution/MODULE, Integrated Power (IPM) - Removal»(ref-352650-S02626081702010010600000) .
3. Remove the four fasteners (2) securing the Front Control Module (FCM) (1) to the Integrated Power Module (IPM) (3).
4. Separate the FCM from the PDC by pulling the two straight away from each other to disengage the electrical connector.

The PCM is a pre-programmed, microprocessor digital computer. It regulates ignition timing, air-fuel ratio, emission control devices, charging system, certain transmission features, speed control, air conditioning compressor clutch engagement and idle speed. The PCM can adapt its programming to meet changing operating conditions.

The PCM receives input signals from various switches and sensors. Based on these inputs, the PCM regulates various engine and vehicle operations through different system components. These components are referred to as Powertrain Control Module (PCM) Outputs. The sensors and switches that provide inputs to the PCM are considered Powertrain Control Module (PCM) Inputs.

The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm, manifold absolute pressure, engine coolant temperature, throttle position, transmission gear selection (automatic transmission), vehicle speed and the brake switch.

The PCM adjusts idle speed based on inputs it receives from sensors that react to: throttle position, vehicle speed, transmission gear selection, engine coolant temperature and from inputs it receives from the air conditioning clutch switch and brake switch.

Based on inputs that it receives, the PCM adjusts ignition coil dwell. The PCM also adjusts the generator charge rate through control of the generator field and provides speed control operation.

Note. PCM Inputs

1. Accelerator pedal position sensor (if equipped)
2. A/C request (if equipped with factory A/C)
3. A/C select (if equipped with factory A/C)
4. Auto shutdown (ASD) sense
5. Battery temperature
6. Battery voltage
7. Brake switch
8. CAN bus (+) circuits
9. CAN bus (-) circuits
10. Camshaft position sensor signal
11. Clutch Interlock Switch (if equipped)
12. Crankshaft position sensor
13. Data link connection for diagnostic scan tool
14. EGR position sensor (if equipped)
15. Engine coolant temperature sensor
16. Fuel level
17. Generator (battery voltage) output
18. Ignition circuit sense (ignition switch in on/off/crank/run position)
19. Intake manifold air temperature sensor
20. Knock sensor(s) (if equipped)
21. Leak detection pump (switch) sense (if equipped)
22. Manifold absolute pressure (MAP) sensor
23. Oil pressure sensor
24. Output shaft speed sensor
25. Overdrive/override switch
26. Oxygen sensors
27. Park/neutral switch (auto. trans. only)
28. Power ground
29. Power steering pressure switch (if equipped)
30. Sensor return
31. Signal ground
32. Speed control multiplexed single wire input
33. Throttle position sensor
34. Transmission governor pressure sensor
35. Transmission output speed sensor
36. Transmission temperature sensor
37. Vehicle speed inputs from ABS or RWAL system

Note. PCM Outputs

1. A/C clutch relay
2. Auto shutdown (ASD) relay
3. CAN bus (+/-) circuits for: speedometer, voltmeter, fuel gauge, oil pressure gauge/lamp, engine temp. gauge and speed control warn. lamp
4. Data link connection for diagnostic scan tool
5. Double start override (if equipped)
6. EGR valve control solenoid (if equipped)
7. Electronic throttle control
8. EVAP canister purge solenoid
9. Five volt sensor supply (primary)
10. Five volt sensor supply (secondary)
11. Fuel injectors
12. Fuel pump relay
13. Generator field driver (-)
14. Generator field driver (+)
15. Generator lamp (if equipped)
16. Idle air control (IAC) motor
17. Ignition coil(s)
18. CAN bus circuits
19. Leak detection pump (if equipped)
20. Natural Vacuum Leak Detection (NVLD) pump (if equipped)
21. Malfunction indicator lamp (Check engine lamp). Driven through CAN bus circuits.
22. Overdrive indicator lamp (if equipped)
23. Radiator cooling fan (if equipped)
24. Speed control vacuum solenoid
25. Speed control vent solenoid
26. Starter relay
27. Tachometer (if equipped). Driven through CAN bus circuits.
28. Transmission convertor clutch circuit
29. Transmission 3-4 shift solenoid
30. Transmission relay
31. Transmission temperature lamp (if equipped)
32. Transmission variable force solenoid

DESCRIPTION - MODES OF OPERATION

The PCM will operate in two different modes: Open Loop and Closed Loop .

During Open Loop modes, the PCM receives input signals and responds only according to preset PCM programming. Input from the oxygen (O2S) sensors is not monitored during Open Loop modes.

During Closed Loop modes, the PCM will monitor the oxygen (O2S) sensors input. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air-fuel ratio. This ratio is 14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the O2S sensor, the PCM can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low emission engine performance.

The fuel injection system has the following modes of operation

1. Ignition switch ON
2. Engine start-up (crank)
3. Engine warm-up
4. Idle
5. Cruise
6. Acceleration
7. Deceleration
8. Wide open throttle (WOT)
9. Ignition switch OFF

The ignition switch On, engine start-up (crank), engine warm-up, acceleration, deceleration and wide open throttle modes are Open Loop modes. The idle and cruise modes, (with the engine at operating temperature) are Closed Loop modes.

The Front Control Module (FCM) (2) contains the software to control the electric shift transfer cases in this vehicle. A separate Transfer Case Control Module (TCCM) is not used. The FCM is a microprocessor-based assembly, controlling the 4X4 transfer case shift functions via the actuation of a shift motor and utilizing the feedback of a mode sensor assembly. Communication is via the CAN bus. Inputs include user selectable 4X4 modes that include 2WD, AWD, 4LOCK, 4LO, and Neutral, depending on the transfer case.

See Electrical - Electronic Control Modules/Electronic Control Modules/MODULE, Front Control - Description for additional information.

The Front Control Module (FCM) utilizes the input from the transfer case mounted mode sensor, the instrument panel mounted selector switch, and the following information from the vehicle's CAN bus to determine if a shift is allowed.

1. Engine RPM and Vehicle Speed
2. Diagnostic Requests
3. Manual Transmission Clutch Switch
4. Brake Applied
5. PRNDL
6. Ignition Status
7. ABS Messages

Once the FCM determines that a requested shift is allowed, it actuates the bi-directional shift motor as necessary to achieve the desired transfer case operating mode. The FCM also monitors the mode sensor while controlling the shift motor to determine the status of the shift attempt.

Several items can cause the requested shift not to be completed. If the FCM has recognized a fault (DTC) of some variety, it will begin operation in one of four Functionality Levels. These levels are

1. Level Zero - Normal Operation.
2. Level One - Only Mode Shifts Are Allowed.
3. Level Two - Only Mode Shifts and Shifts Into LOW Are Allowed (No Neutral Shifts Are Allowed).
4. Level Three - No Shifts Are Allowed

The FCM can also be operating in one of three possible power modes. These power modes are

1. Full Power Mode is the normal operational mode of the module. This mode is achieved by normal CAN bus traffic being present and the ignition being in the RUN position.
2. Reduced Power Mode will be entered when the ignition has been powered off. In this state, the module will shut down power supplied to external devices, and to electronic interface inputs and outputs. From this state the module can enter either Sleep Mode or Full Power Mode. To enter this mode, the module must receive an ignition message denoting that the ignition is off, or not receive any messages for 5 ±0.5 seconds. To exit this mode, the module must receive one ignition message that denotes that the ignition is in the RUN position.
3. Sleep Mode will be entered, from the Reduced Power Mode, when no CAN traffic has been sensed for 20 ±1 seconds. If during Sleep Mode the module detects CAN bus traffic, it will revert to the Reduced Power mode while monitoring for ignition messages. It will remain in this state as long as there is traffic other than run or start messages, and will return to Sleep mode if the bus goes without traffic for 20 ±1 seconds.

The Transmission Control Module (TCM) is a sub-module within the Powertrain Control Module (PCM) (1) . The PCM is attached to the right-inner corner of the engine compartment.

The Transmission Control Module (TCM) controls all electronic operations of the transmission. The TCM receives information regarding vehicle operation from both direct and indirect inputs, and selects the operational mode of the transmission. Direct inputs are hard wired to, and used specifically by the TCM. Indirect inputs are shared with the TCM via the vehicle 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+) (if equipped)
4. Throttle Position Sensor
5. Crankshaft Position Sensor
6. Transmission Range Sensor
7. Pressure Switches
8. Transmission Temperature Sensor
9. Input Shaft Speed Sensor
10. Output Shaft Speed Sensor
11. Line Pressure 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. Engine Coolant Temperature
6. Ambient/Battery Temperature
7. 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
3. Torque Reduction Request

Some examples of TCM indirect outputs are

1. Transmission Temperature (to PCM)
2. PRNDL Position (to cluster/CCN)

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

1. Storing and maintaining Clutch Volume Indexes (CVI)
2. Storing and selecting appropriate Shift Schedules
3. System self-diagnostics
4. Diagnostic capabilities (with scan tool)

Note. If the TCM has been replaced, the "Quick Learn Procedure" must be performed. See Electrical - Electronic Control Modules/Electronic Control Modules/MODULE, Transmission Control - Standard Procedure