Bus and Diagnostics Communication: Other Saab 9-5 I рестайлинг

Connected components

CONNECTED COMPONENTS

Scheme 163

Scheme 164

Location: On the left-hand ground screw in the middle of the knee member (in the interior).

CONNECTED COMPONENTS

Condition

The following conditions are applicable

Trionic

1. Engine has started
2. No communication for 10 seconds

The following conditions are applicable

Trionic

1. Engine has started
2. No communication for 10 seconds

TCM

1. The automatic transmission input shaft speed exceeded 200 RPM once during the present driving cycle.
2. No communication for 6 seconds.

The following conditions are applicable

Trionic

1. Engine has started
2. No communication for 3 seconds.

The following conditions are applicable

TCM

1. The automatic transmission input shaft speed exceeded 200 RPM once during the present driving cycle
2. No communication for 4 seconds.

The following conditions are applicable

Trionic

1. Engine has started
2. The TCM has been present on the bus at some time previously
3. No communication for 3 seconds.

The following conditions are applicable

Trionic

1. No bus communication for 3 seconds.
2. TC/ABS has been present on the bus at some time previously.

Control module

When the control module is supplied with current, the processor in it is tripped. The processor then reads the instructions stored in the control module's memory.

The control module is programmed to read the inputs and activate the outputs. If the control module program is faulty, the diagnostic trouble code "Internal Control Module Fault" will be generated.

The control module must be supplied with current before the system will function. The control module is supplied with current and the processor tripped when the control module can be contacted by the diagnostics instrument.

Outputs

The purpose of the system is to control a number of functions by means of various actuators, such as an injector or lamp. For the system to be capable of performing its functions, it must be possible to activate the actuators. For this reason the actuators must be connected to the control module and have a proper power supply or ground connection.

Inputs

A condition for the control module's capability of controlling its actuators is that the system's sensors supply it with correct values.

Sensor performance can be checked with the diagnostics instrument.

1 No communication with the DICE.

If the Tech 2 cannot contact the DICE, neither can it check that the control modules connected to a bus are communicating correctly. The fault is probably because the DICE is not supplied with current or the diagnostics cable is not connected to the DICE (pin 7 of the data link connector and pin 28 of the DICE). The following menu will appear on the Tech 2

DICE (Dashboard ICE)

NO CONTACT WITH ANY BUS SYSTEM CAUSE No communication with DICE DIAGNOSTIC PROCEDURE Check the selected car model Turn the ignition key to ON Press < ENTER and try again If there the trouble persists: See FAULT DIAGNOSIS 'No contact with any bus system' in Service Manual 3:5 'Bus and diagnostics communication'.

If < ENTER is pressed, the Tech 2 will again try to contact the DICE. If the < EXIT key is pressed, the Tech 2 will try to contact the selected control module (the reason for this is that it should be possible to contact the SRS (Airbag) or ABS even if the DICE is not present).

2 No communication with one or more control modules connected to a bus

If the Tech 2 is in communication with the DICE but one or more control modules connected to a bus are missing, the following menu will appear on the Tech 2

Checking bus communication

NO CONTACT WITH ONE OR MORE BUS SYSTEMS CAUSE One or more control modules are not communicating on the bus DIAGNOSTIC PROCEDURE Press < OK to show missing control module(s) See FAULT DIAGNOSIS by fault systems 'No contact with one or more bus systems' in Service Manual 3:5 'Bus and diagnostics communication'.

OK

If < OK is pressed, a list of the control modules fitted as original equipment on the car will be displayed. "OK" is shown on the right of each control module if it is communicating correctly and "Missing" if the control module is missing from the bus.

BUS CONFIGURATION CHART

Regardless of whether < ENTER or < EXIT is pressed, the Tech 2 will try to communicate with the selected control module. If the Tech 2 cannot contact the selected control module, the following menu will appear

MIU (Main Instrument Unit)

NO COMMUNICATION WITH VEHICLE Check selected car model Press < ENTER to try again Press < EXIT to end If the trouble persists: See FAULT DIAGNOSIS by fault symptoms 'No communication with vehicle' in Service Manual 3:5 'Bus and diagnostics communication'.

3 No communication with the SRS (Airbag) or ABS

The fault is probably because the Airbag or ABS control module is not supplied with current or the diagnostics cable is not connected to the control module. If the Tech 2 cannot contact the Airbag or ABS, the following menu will appear

Airbag

NO COMMUNICATION WITH VEHICLE Check selected car model Press < ENTER to try again Press < EXIT to end If the trouble persists: See FAULT DIAGNOSIS by fault symptoms 'No communication with vehicle' in Service Manual 3:5 'Bus and diagnostics communication'.

Changing car configuration

If a new control module connected to a bus is installed in the car, the list will be filled in automatically.

If a control module connected to a bus, such as the CD changer, is removed from the car, the list can be reset to zero with a command under "All systems/Read/Clear Configuration" or "DICE/Read/Clear Configuration".

BUS CONFIGURATION CHART

Scheme 165

It is our experience that the majority of control modules returned to us for repair or replacement under warranty are in perfect working order. In these cases, fitting a new control module has obviously not cured the fault. Therefore, go through all the following points carefully before changing the control module

Scheme 166

1. Check the latest edition of TIS2000 to see whether the problem can be solved with a control module software update (for control modules that can be reprogrammed). IMPORTANT: Avoid SPS programming unless it is absolutely necessary. It is extremely important to follow the instructions for SPS programming to avoid damaging the control module.
2. Check all grounding points and the power supply to the control module.
3. Check with a diagnostic tool that all the readings are plausible (several readings can affect one function).
4. Check with the diagnostics tool that all activations function normally. (Malfunction in one output circuit can affect another output circuit).
5. If the fault persists, the control module must be changed. Fill in the "Checklist for changing turbocharger and engine control module" before changing the control module and attach it when the control module is returned.
6. Control modules are sensitive to electrostatic discharges. Great care must be taken to follow the following procedure to avoid damaging internal components in the control module: Keep the control module in its packaging for as long as possible. Never touch the pins of a control module with your hands or clothing. Ground yourself by touching part of the car's body/engine. Unplug the connector from the car's control module. Place the exchanged control module in its return packaging without touching the pins. Ground yourself by touching part of the car's body/engine. Plug in the connector to the car's control module.

Scheme 167

A suitable instrument to use is a multimeter.

The ohmmeter must not be used to test components containing semi-conductors, e.g. control modules and relay with timing functions, etc.

When measuring resistance, the power supply to the system being tested must be disconnected as the measuring instrument generates a weak current in the circuit in question.

This is done to ensure that there is no current already in the tested circuit and that the correct reading is obtained.

Scheme 168

Scheme 169

1. Turn on the load.
2. Set the multimeter for measuring voltage and connect the negative lead of the voltmeter to a good grounding point.
3. Connect the positive lead of the voltmeter to the point where the voltage is to be read.
4. On the output side of switches/control modules, it is better to start checking from these and gradually work your way towards the load. When there is no longer a voltage reading, you will have gone past the break point.
5. On the input side of switches/control modules/consumers, it is better to start at the power source (normally a fuse) and then move gradually towards the switch/control module/consumer. When there is no longer a voltage reading, you will have gone past the break point.

Scheme 170

Scheme 171

1. Make sure the component or lead to be tested is not under tension (e.g. by removing the relevant fuse).
2. Set the multimeter for measuring ohms and connect the ohmmeter to each end of the component/lead to be tested.
3. Jiggle the relevant wiring harness while observing the ohmmeter. Normally, the resistance of a wiring harness is less than 1 ohm. Specified values apply to components.

Scheme 172

Scheme 173

1. Make sure the lead being tested is not under tension (e.g. remove the relevant fuse) and that any loads are disconnected.
2. Set the multimeter for measuring ohms.
3. Connect one test lead to a good ground and the other to the point to be tested.
4. Carefully jiggle the wiring harness and make sure the multimeter reading shows infinite resistance (OL) all the time.

Scheme 174

Scheme 175

Scheme 176

Scheme 177

Scheme 178

Scheme 179

Scheme 180

1. When unplugging a connector that has a catch, the catch must be undone first before parting the connector. Make sure the connector catch engages properly when plugging in the connector. Examples of some of the different types of connector in the car: 1.A. Pull out the sheath to undo the connector catch. After plugging the connector in, press in the sheath to lock the connector. NOTE: Use a small screwdriver to help undo the catch on the connector. 1.B. Press in the catch to release the connector. Make sure the connector is securely locked when plugged back in. 1.C. Pull out the sheath to undo the connector catch. After plugging the connector in, press in the sheath to lock the connector. 1.D. Press in the catch on the wire clamp and tip the wire forward. Plug in the connector and lock it by raising the wire clamp. NOTE: Make sure the wire clamp is locked in the correct position, to ensure good contact in the connector. 1.E. Raise the catch to release the connector. Make sure the connector is securely locked when plugged back in. 1.F. Press in the catch on the connector to release the wire clamp. Release the connector sheath and fold forward the wire clamp. NOTE: Using greater force than necessary attempting to fold the wire clamp forward before the sheath has been released can damage the connector. Plug in the connector and lock it by raising the wire clamp.
2. Ground yourself, by touching the car's body or engine, when unplugging or plugging in the connectors on the car's control modules.
3. Never unplug a connector by pulling the wiring.
4. Never touch the pins on a control module with your hands or clothes. IMPORTANT: Incorrect handing or the use of the wrong tool can damage the sleeves in the connector. Use a test cable (part no. 86 12 731) of the correct size to avoid damaging the sleeves in the connector.
5. When taking measurements, use only probes designed for this purpose to avoid damaging the contacts. Use a test cable (part. no. 86 12 731) of the correct size.
6. For repairs to connectors, the correct special tools and spare parts must be used.
7. The following connectors may not be repaired: Screened cables/coaxial cable (e.g. ABS sensor cable) Airbag system and pyrotechnic belt pretensioner system High-tension cables (e.g. ignition system, xenon headlamps).

Scheme 181

Scheme 182

1. Check that there are no problems with contact on connection.
2. Check contacts, connectors and crimps for oxidation, withdrawn pins and pin clamping force. IMPORTANT: Incorrect handing or the use of the wrong tool can damage the sleeves in the connector. Use a test cable (part no. 86 12 731) of the correct size to avoid damaging the sleeves in the connector.
3. To check the clamping force, use a test cable with the correct size pins (from set 86 12 731). NOTE: A test cable with too large pins will damage the sleeves in the connector. Insert the test cable pin into the connector to check the pin clamping force. Poor clamping force can cause intermittent contact. Check also that the pin is aligned with the other pins in the connector. A pin that is recessed (pushed out) can cause intermittent breaks.
4. Check the wiring and connections for breaks.
5. Check the wiring harness, connectors and ground connections.

Scheme 183

The following conditions are applicable

1. Battery OK.

The following conditions are applicable

1. Ignition switch in ON position

The following conditions are applicable

1. Ignition switch in ON position

The following conditions are applicable

1. Ignition switch in ON position

Control Module Connections

A simple means of checking whether the control modules are operative and allow diagnostics communication (column B) is given for each control module (column A) in the table below.

If the control module is not operative, check whether it is supplied with current and grounded (columns C-E).

Then check whether the control module is connected to the bus (column F) or the data link connector (column G).

Note. Some control modules also have other supplies of current and ground connections but these are not necessary for diagnostics communication.

CONTROL MODULE CONNECTIONS TECHNICAL DATA

Scheme 184

Scheme 185

1. Trionic, engine management system (430/589/600/608)
2. TCM (Transmission Control Module), control module for automatic transmission (502)
3. TC/ABS (Traction Control) (382)
4. P bus (Powertrain bus)
5. MIU (Main Instrument Unit) (540)
6. I bus (Instrument bus)
7. SID (Saab Information Display) (541)
8. TWICE (Theft Warning Integrated Central Electronics) (632)
9. ACC (Automatic Climate Control) (216)
10. Audio system, main unit (353)
11. CDC (CD changer) (355)
12. PSM (Power Seat Memory) (357Dk)
13. PMM (Power Mirror Memory) (611)
14. DICE (Dashboard Integrated Central Electronics) (628)
15. Data link connector (H16-5/445)
16. Airbag (SRS) (331)
17. ABS (Anti-lock Brake System) (547)
18. SPA (Saab Parking Assistance) (630)

Scheme 186

P bus and I bus in the Saab 9-5

All control modules in the Saab 9-5 are connected to the bus with the exception of ABS and SRS. For cars with Traction Control, the TC/ABS control module is connected to the bus.

The bus allows large quantities of data to be sent between the control modules on only two cables. The bus is divided into a Power train bus (P bus) and an Instrument bus (I bus).

Trionic, TCM and TC/ABS power train systems require fast data communication so that no noticeable delay occurs, e.g. for torque limitation when changing gears.

Trionic, TCM and TC/ABS are connected to the P bus, on which data transfer is ten times faster than on the I bus.

The P bus and I bus are connected to the MIU. The MIU is responsible for making information on one bus available to the other bus.

The diagnostic instrument is not connected directly to the bus but communicates via the DICE, one of the control modules connected to the I bus, and so has access to all control modules connected to the bus.

Vehicle speed data is important for many control modules. Since the ABS is not connected to the bus, the vehicle speed signal is sent on a separate lead from the ABS to the MIU. The MIU then sends the data over the busses. In cars with Traction Control, the TC/ABS sends vehicle speed data to the MIU via the P bus.

P-Bus And I-Bus

A bus is understood to be the leads over which information is sent digitally and serially. Digital means that the voltage difference between the leads has only two values, roughly 0 V and 5 V. The information is coded so that different combinations of 0 V and 5 V pulses have different meanings.

Serial means that the information is sent in "packets" which are transmitted one after the other in rapid succession.

All control modules in the Saab 9-5 are connected to the bus with the exception of ABS and SRS. For cars with Traction Control, the TC/ABS control module is connected to the P-bus.

The buses consist of a P-bus (Powertrain Bus) and an I-bus (Instrument Bus). Both buses are connected to the MIU (Main Instrument Unit). The buses are electrically isolated from each other.

The diagnostic tool is not connected direct to the bus but communicates via the DICE, one of the control modules connected to the I-bus, and so has access to all control modules connected to the bus.

The data transfer rate of the P-bus is ten times faster than that of the I-bus. The reason for this is that the powertrain systems need information with the least possible delay, as for example when providing air mass compensation when the selector lever is moved from N to D or torque limitation in connection with gear changing.

All information sent out on a bus by a control module is available to all other control modules connected to a bus. The MIU ensures that information which is available on one bus is also available on the other.

The control modules send out information on the bus at regular intervals. The time between two transmissions depends on the information being sent and varies between 10 milliseconds (0.010 seconds) and 1 second. Information is also sent out by the control modules whenever the information changes.

Information interchange between control modules takes place on two leads, bus+ (green lead) and bus-(white lead). The two P-bus leads are twisted to increase their resistance to electrical interference.

Scheme 187

The bus may be regarded as a two-wire telephone line running between the control modules.

Communication is continuous once the ignition switched on. With the ignition switched off, a control module that is operative may if necessary awaken the other control modules. This happens for example when a door is opened and TWICE, to which the door switches are connected, awakens the others so that DICE will be able to switch on the interior lighting.

When one of the control module microprocessors "speaks" the other control modules listen regardless of whether or not the information is of interest to them. MIU transfers an assortment of information between the buses. This way, information sent by one control module is available to all control modules connected to the bus.

With the bus system, analogue signal leads such as those for the turbo/APC pressure signal for the MIU, and digital signal leads such as those for PWM throttle position signals and frequency modulated engine speed signals, can be eliminated and the number of sensors consequently reduced.

The Trionic system, which is connected to a bus, has a coolant temperature sensor. This means that the temperature of the coolant is always available to all systems. For this reason, only one coolant temperature sensor is needed in the car.

The coolant temperature is used by DICE for controlling the radiator fans (see illustration), by the MIU for controlling the temperature gauge, and by the ACC for controlling ventilation fan speed and air distribution during cold starts.

Basically, the control modules connected to a bus are like one big control module with a number of sensors and a number of actuators. Bus communication may be regarded as internal control module communication.

This means that an overall view of the car is essential when carrying out fault diagnosis. A malfunction need not necessarily be caused by a fault in the system where it occurs but may very well be caused by a defective sensor in another system.

Scheme 188

Scheme 189

Scheme 190

A control module sends a message by transmitting ones and zeros in a definite order. The control module sends the message only if no other control module is transmitting. What the various combinations of ones and zeros mean is determined in advance so that all control modules interpret the information identically. The message contains a description of what is sent and its value, e.g. "Coolant temperature 100°C" or "A/C On".

The two bus leads are supplied with about 2.5 V from each control module. This is accomplished by means of three resistors connected in series between 5 V and ground. The middle resistor ensures that the current on bus+ is slightly lower than that on bus- when no messages are being sent.

When both leads are supplied with about 2.5 V for a certain period of time (2 millionths of a second on the P bus), a one will be transmitted. To transmit a zero, the control module pulls bus+ almost to 5 V and bus-almost to ground for an equal period of time.

Note that a long sequence of ones is the same as no message being transmitted.

Scheme 191

When a control module transmits, all other control modules listen to it. They do this by looking at the difference in voltage between bus+ and bus-. (A voltage difference close to 0 V is interpreted as a one and a difference close to 5 V as a zero.)

What the various combinations of ones and zeros mean is determined in advance so that all control modules interpret the information identically. The message contains a description of what is sent and its value, e.g. "Coolant temperature 100°C" or "A/C On".

Electrical interference, such as from a relay, will affect the voltage on both leads in the same direction. The difference in voltage will not be affected, however, and this makes the bus extremely insensitive to interference.

Messages

Below is a summary of the messages which are sent out by all the systems in the car that are connected to a bus. It also shows which systems use the transmitted information. The purpose of the summary is to help you gain an understanding of the car's functional relationships, which is a fundamental prerequisite for rapid fault diagnosis.

DICE

DICE MESSAGE TRANSMITTING

TWICE

TWICE MESSAGE TRANSMITTING

ACC

ACC MESSAGE TRANSMITTING

Audio system, main unit

AUDIO SYSTEM MESSAGE TRANSMITTING

CDC

CDC MESSAGE TRANSMITTING

PMM

PMM MESSAGE TRANSMITTING

MIU

MIU MESSAGE TRANSMITTING

SID

SID MESSAGE TRANSMITTING

PSM

PSM MESSAGE TRANSMITTING

Trionic

TRIONIC MESSAGE TRANSMITTING

TCM

TCM MESSAGE TRANSMITTING

SPA

SPA MESSAGE TRANSMITTING

TC/ABS

TC/ABS MESSAGE TRANSMITTING

Scheme 192

In the bus system a large number of function chains can be identified. Below are three examples of important ones.

Cars with ABS

Vehicle speed is sensed by the ABS through an inductive sensor at each wheel. The sensor supplies the control module with alternating current, the amplitude and frequency of which increase with increasing wheel speed. The frequency is proportional to wheel speed, 29 Hz at a speed of one wheel revolution per second. The ABS control module uses the 4 wheel speeds to prevent wheel lock-up on braking.

Several other systems in the car require wheel speed data. Cars with an ABS control module that is not connected to the bus have a control module output for each wheel. A transistor grounds each output 29 times per wheel revolution.

The main instrument unit is connected via a lead to the wheel speed signal output for the rear left wheel. A rear wheel has been chosen as the most accurate measurement of distance is provided by a non-drive wheel. The frequency modulating signal is converted in the main instrument to km/h. The main instrument unit makes a correction for the programmed tyre type.

Cars with TC/ABS

In cars with Traction Control the TC/ABS control module is connected to the P bus. The TC/ABS control module transmits the wheel speed for all four wheels but only the speed data from the rear left and front right wheels is used.

RL wheel speed: The TC/ABS control module transmits the bus message "rear left wheel speed xxx km/h". This message is used by the MIU (internally). The MIU transmits "Vehicle speed" over the P bus and I bus.

FR wheel speed: The TC/ABS control module transmits the bus message "front right wheel speed xxx km/h". This message is used by the Trionic.

Since the main instrument unit is connected to a bus, all control modules connected to the bus are supplied with information on the speed of the left-hand rear wheel and the odometer reading.

In the table of transmitted bus messages it can be seen that the MIU transmits the vehicle speed and that this is used by: Trionic, SID, ACC, Audio and TWICE. The MIU also transmits the odometer reading and this is used by the SID for the service indicator.

The various systems use the vehicle speed for the following functions

1. There is a separate lead from the ABS to the Trionic for front right wheel speed. In cars with Traction Control, the Trionic receives wheel speed information via the bus. The bus value is used for safety for the cruise control system; both values must exceed 40 km/h for the cruise control to work. The value is also used as a replacement value in case the front right wheel speed should fail.
2. The DICE uses the value to activate the radiator fans for A/C on, high outside temperature and low speed.
3. The SID uses the value for trip computer functions.
4. The ACC uses the value for activating recirculation in connection with high outside temperature and low speed.
5. The Audio system uses the value for increasing the volume at high speeds.
6. The TWICE uses the value for automatic locking of the doors when driving off (certain markets).

The ABS has extremely good diagnostics for its wheel sensors. This means that with a high degree of certainty the wheel speed signals will be present on the control module's four outputs if no diagnostic trouble codes have been generated in the system.

Neither the main instrument unit nor any of the other bus systems have speed signal diagnostics for the rear left wheel. If the speedometer is working, however, it is certain that speed information is present on the bus and consequently available to all systems connected to the bus.

If the speedometer is not working, the speed reading obtained on any bus system is always 0, and there are no diagnostic trouble codes in the ABS, then the fault is probably in the lead between the ABS and MIU.

The Trionic has diagnostics for the front right wheel but it may take a long journey without a speed signal for the diagnostic trouble code to be generated.

A readout of the two speed signals used in the car can be obtained from the Trionic using the diagnostic tool.

Scheme 193

Scheme 194

When the ignition is turned on the TWICE checks that the right key is inserted in the ignition switch. A circuit built into the remote control part of the key sends a code by means of inductance to a coil round the ignition switch under the centre console. The code is passed on to the control module which checks that it is correct. The TWICE also checks that the right MIU is fitted in the car. The MIU continuously sends out an ID number on the bus.

If the key and the MIU's ID number are OK, the TWICE sends out the message "Immobilization OFF" on the bus. This information is used by the Trionic which cancels fuel shut-off, which is always activated every time the ignition is switched on.

If the TWICE, MIU or Trionic control module is replaced, immobilizing must be reprogrammed in the TWICE. If this is not done, the engine will not start and diagnostic trouble code P1460 will be generated in the Trionic.

If immobilization is not reprogrammed in the TWICE, the following diagnostic trouble codes are generated in the TWICE: DTC B1780 if the Trionic has be replaced; DTC B1782 if the MIU has be replaced.

If the diagnostic trouble code is generated in spite of programming having been carried out, fault diagnosis will have to be carried out on the immobilization function in the TWICE.

Scheme 195

A number of conditions must be fulfilled for the A/C relay to be grounded and the electromagnetic clutch of the A/C to engage.

In AUTO mode the ACC unit will request the DICE for A/C engagement if

1. Outside temperature (information via bus from the SID) is above 0°C.

The DICE then requests the TRIONIC control module to ground the A/C relay if the following conditions are fulfilled

1. Coolant temperature (information via bus from the Trionic) is below 125°C.
2. Refrigerant pressure (own sensor) on the high-pressure side is between 2 and 27 bar.
3. The temperature in the evaporator (own sensor) must fulfil the following conditions: 3.a. If the temperature in the evaporator is above 3°C, the DICE sends via the bus a request to the Trionic control module for A/C engagement. 3.b. If the temperature in the evaporator is below 0°C, the A/C compressor can only be engaged if the conditions in points 4 and 5 are satisfied.
4. The outside temperature (information via bus from the SID) must be above 25°C.
5. One of the following conditions must also be met: 5.a. The engine must not have been running for more than 30 minutes (information via bus from the Trionic control module). 5.b. Vehicle speed is below 5 km/h (information via bus from the MIU). The Trionic will then activate the compressor relay.

In the event of a fault in any of the aforementioned sensors in the systems concerned, the A/C compressor will not work. The function chain clearly shows the importance of obtaining diagnostic trouble code readouts from all systems because several systems are involved in any given function.

If there are no diagnostic trouble codes with the "A/C not working" symptom description, all input values which can block the function must be checked methodically by means of the diagnostic tool's read value commands. The compressor relay is activated in the Trionic system. Then carry out fault diagnosis in the system which "owns" the defective sensor or actuator.

Scheme 196

Scheme 197

The two systems which are not connected to a bus, ABS and SRS, are each connected to pin 8 of the data link connector through their own communications lead.

The diagnostic tool communicates digitally and serially with the selected system. Digital means that the voltage difference between the lead and ground has only two values, in this case roughly 0 V and B+. The information is coded so that different combinations of 0 V and B+ pulses have different meanings, e.g. whether the SRS or ABS is to be called.

Serial means that the information is sent in "packets" which are transmitted one after the other in rapid succession.

In cars with Traction Control the TC/ABS control module is connected to the P-bus but diagnostics communication takes place via the K lead.

If none of the systems can be contacted, the fault may be either in the car or in the diagnostic tool. If the diagnostic tool can contact one of the systems concerned in another car, then the fault is in the car.

In that case, first check that the control module is awake. The ABS and SRS warning lamps are tested by the control module as soon as the ignition is switched on. If the control module is awake, then the fault is probably in the lead between the data link connector and the control module.

If Trionic cannot communicate with the TC/ABS for 3 seconds while driving, diagnostic trouble code P1625 will be generated.

Other Systems

All other systems are connected to a bus and communicate with each other via the bus. The DICE is connected by a communications lead to pin 7 of the data link connector.

The diagnostic tool communicates digitally and serially with the DICE. Digitally means that the voltage difference between the lead and ground has only two values, in this case about 0 V and B+.

Serial means that the information is sent in "packets" which are transmitted one after the other in rapid succession.

Through contact with the DICE, the diagnostic tool has access to all control modules that are connected to a bus.

If, for example, the TCM is contacted, the diagnostic tool will first call the DICE and request diagnostics communication with the TCM. The DICE passes along the diagnostic tool's request on the I bus, following which the MIU forwards the diagnostics communication request to the P bus and the TCM.

This means that both the DICE and the MIU must be supplied with current (awakened) before the TCM can be contacted.

Scheme 198

Scheme 199

If no system connected to a bus can be contacted, the fault could be either in the car or the diagnostic tool. If the diagnostic tool can contact any of the systems concerned in another car, then the fault is in the car.

For further information on diagnosing faults in diagnostics communication with the DICE or other system connected to a bus, see the following " BUS DIAGNOSIS " section.

Scheme 200

Scheme 201

In a bus system, all units must be capable of communicating with each other. For example, the engine cannot be started unless the Trionic system can receive the immobilization information sent out by the TWICE.

Bus faults can be caused by a bus lead breaking. This could result in one or more systems disappearing from the bus concerned (I or P), depending on where the break in the wiring harness occurred.

If a short circuit occurs in a bus lead, all systems will disappear from the bus concerned (I or P).

Note that if a short circuit occurs in the I-bus, then the DICE is the only bus system which can be contacted with the diagnostic tool.

In the event of a fault in grounding or power supply to one or more systems, these will cease to communicate.

Permanent bus faults

All diagnostics communication with systems connected to a bus takes place via the DICE.

Irrespective of which system is contacted, the diagnostic tool will first check with the aid of the DICE that all systems in the car connected to a bus are awake and in communication.

If any control module connected to a bus is missing, the diagnostic tool will show this. This means that all control modules connected to a bus are communicating correctly unless the diagnostic tool indicates otherwise with a warning.

Intermittent bus faults

The Trionic and TCM continuously check that all control modules from which they obtain information communicate correctly. In the case of intermittent faults in bus communication with any of these systems, diagnostic trouble codes will be generated in the Trionic and TCM. The cause of the fault could be that the control module concerned has lost its power supply or one of the bus leads.

Incorrect values on the bus

A diagnostic trouble code will be generated in the Trionic and TCM if any information they obtain from the bus has an incorrect value. The diagnostic trouble code text will refer to the system where the fault is present.