Diagnostic Principles

Principle of Operation-Diagnostics





Traction Control System (TCS) control module communication with an ISAT (scan tool) goes via pin 9. Communication is two-way and consequently consists of both input and output signals. The diagnostics socket is located under the dash on the drivers side of the car. With the ignition switch in the Drive position, the voltage on pin 9 is the same as battery + when the ISAT is connected and O V when the ISAT is not
connected.

For communication between the ISAT and the TCS control module to be possible:
- The ignition switch must be in the Drive position.
- Engine speed must be 1500 rpm (if the engine is running).
- The TCS must be contacted.

The ISAT has no contact with the system if:
- The diagnostics lead to pin 9 of the control module is defective.
- The ground connection on pins 13 and 30 is not good.
- no voltage is present on to pin 28 or pin 32.
- the circuit to pin 3 is shorted to battery +.

TCS Indicator Lamp

When the ignition switch is turned to the drive position the indicator lamp lights up for three seconds.




In the case of wheelspin that requires engine torque to be reduced by more than 7%, the indicator lamp lights up after a slight delay (360 ms). In the case of torque reduction greater than 30%, however, the lamp lights up at once. The indicator lamp then stays alight as long as the system remains in operation, but always for at least one second.
The indicator lamp is caused to light up by the control module grounding pin 12. Simultaneously, the circuit to pin 4 of the control module for the electronic gearbox is also grounded. This module then starts to control shift performance as a function of the TCS throttle butterfly's position signal from the TCS control module instead of the main throttle butterfly's position signal from the MOTRONIC control module. However, the shifting points are still determined by the position of the main throttle butterfly.

The position signal for the TCS throttle butterfly goes from pin 4 of the TCS control module to pin 15 of the automatic transmissions Traction Control Module (TCM) control module.

TCS Off Warning Lamp




When the ignition switch is turned to the Drive position the warning lamp lights up for three seconds.
The warning lamp remains on in the event of a system fault and is caused to light up by the control module grounding the lamp circuit on pin 26.
The warning lamp also lights up when the system is disconnected manually, which can be done at speeds lower than 60 km/h by pressing the TCS switch. The system can be engaged at any speed by pressing the TCS switch. The TCS OFF lamp will then go out again.

If ON lights up in connection with starting, the system is always engaged automatically.





ON/OFF Switch

NOTE: This switch is of spring-loaded type and makes contact only when the button is pressed. By pressing the button a pulse is sent to the control module which causes it to either engage or disengage the TCS system. Accordingly, it is not possible to see whether the system is manually engaged or disengaged just by looking at the position of the button. This can be verified by looking at the TCS OFF lamp.

The ON/OFF switch can be used to switch off the system at speeds lower than 60 km/h or to engage the system at any speed.

The TCS switch has two connections, one to pin 1 of the control module and the other to ground. When the button is pressed, the circuit closes and the system is either engaged or disengaged, depending on its status.

If the circuit to pin 1 of the control module is shorted to ground, a diagnostic trouble code will be generated and the system cannot be disengaged. The same trouble code will also be generated if the TCS switch is pressed continuously for more than 10 seconds.

The system is always engaged in connection with starting when the ignition switch is turned to the Drive position.

TCS Throttle Body





Principal of Operation

The TCS throttle body consists of a body, butterfly, electric motor and linkage. It is mounted after the regular throttle body and cannot be installed the wrong way round.

In Limp-Home mode there is no extra cable to regulate the TCS throttle butterfly. Instead, the power supply for the electric motor is switched off and the spring sets the butterfly to the wide open position.

NOTE: No adjustment must be made to the throttle butterfly.

The motor is a DC motor supplied with a 500 Hz PWM output from pins 18 and 35 of the control module. The motor can be run in both directions.
As a spare part, the TCS throttle body is replaced as a complete unit.





Information from the TCS throttle butterfly position sensor is received on pin 27 of the control module. Depending on the position of the TCS throttle butterfly, the voltage will vary between about 1.1 and 4.4 V. The position sensor is supplied with 5 V from pin 3 of the control module and grounded via pin 20.

On cars with automatic transmission, a PWM signal sent out via pin 4 of the TCS control module gives the position of the TCS throttle butterfly. This signal is received by the control module for the automatic transmission. It has a voltage of about 1.6 V when the butterfly is closed and about 8.5-11 V when it is open.

Power Supply For The Throttle Actuator Motor
The TCS throttle actuator motor is supplied with a 500 Hz pulse width modulation (PWM) output from pins 18 and 35 of the control module. When the butterfly is closed the voltage across pins 18 and 35 is about 3.5 V.

Diagnostic trouble codes are generated, the TCS OFF lamp lights up and the system is rendered inoperative in the event of a mechanical or electrical fault in the actuator motor or position sensor, or in connecting leads.





Principle Of Operation - Main Throttle Butterfly Position Signal
In order to synchronize the TCS throttle butterfly with the main throttle butterfly, the TCS control module obtains a position signal on pin 11 from pin 54 of the MOTRONIC control module. This signal, which is a 100 Hz PWM signal, gives the position of the main throttle butterfly and with the engine running at idling speed measures about 1.2 V.

In the event of an incorrect butterfly position signal or if there is no continuity or a short in the circuit, then diagnostic trouble codes are generated, the TCS OFF lamp lights up and the system is rendered inoperative.

When the ignition switch is turned to the Drive position, and also when
the starter motor is in operation, the MOTRONIC control module sends an engine temperature signal as an operational check instead of a butterfly position signal to pin 11 of the TCS control module.

With the engine switched off and the ignition switch in the Drive position, the signal measures about 1.25-1.0 V, depending on the temperature of the engine.

If the engine temperature signal is incorrect, diagnostic trouble codes will be generated in the MOTRONIC system. No diagnostic trouble code will then be generated in the TCS system.

Principle of Operation-Speed signals




To determine whether wheelspin occurs at any of the drive wheels, the control module obtains information on the speed of the front wheels. Since the speed of the rear wheels is used as a reference value, this information is also received by the control module.

The speed of each wheel is obtained from the ABS control module as follows:
- The signal is a square wave which varies periodically between approx. battery + and 0 V 29 times per wheel revolution. For a stationary wheel the voltage may be either battery or 0 V.
- If one or more wheels are stationary at the same time as any other wheel exceeds 10 km/h, a diagnostic trouble code will be generated. Should the fault persist for longer than 20 seconds, the TCS OFF lamp will light up and the system will be rendered inoperative.
- Similarly, the system will be rendered inoperative if the speed of any wheel exceeds 280 km/h.

Principle of Operation-Engine Speed




Information on current engine speed is obtained via pin 6 of the TCS control module from pin 43 of the MOTRONIC control module.
Information on engine speed is necessary to enable:
- the control module, together with information on the positions of the main throttle butterfly and the TCS throttle butterfly, to calculate engine torque
- the control module, together with speed signals from the wheels, to calculate the appropriate gear.

The signal is a square wave measuring about 40 Hz at idling speed and about 125 Hz at 2500 rpm. In the event of an incorrect signal or if there is no continuity or a short in the circuit, then diagnostic trouble codes are generated, the TCS OFF lamp lights up and the system is rendered inoperative.

Principle of Operation- Input from Brake Light Switch




The control module receives current via the brake light switch to pin -,4 if the brakes are activated.

Brake light switch is used also if the driver decides to pump brake.
Each time the driver depresses the brake pedal, the ABS modulation will start again from the output position and the lamp will indicate that the electronic control module is receiving voltage from the brake fight switch. The electronic control module input from the brake light switch is continually monitored and grounded via the brake light switch. If a circuit fault occurs the diagnostic trouble code is registered but the ABS warning lamp will not come on. ISAT

Principal of Operation-Cruise control Disengagement




As soon as the Traction Control System is activated or the brake pedal depressed, battery + is sent via pin 5 of the control module to pin G of the Cruise Control, which is then disengaged.

NOTE When the TCS is activated, Cruise Control disengagement occurs after a delay of about one second.

Disconnection of Full-Load Enrichment





Activation

If the TCS is activated at full throttle, the MOTRONIC system's normal full-load enrichment must be inhibited. This is because the TCS now controls the engine load via the TCS throttle butterfly and because the input from the main throttle butterfly to the MOTRONIC control module no longer provides correct information. When the TCS is activated, a 62 Hz PWM signal goes from pin 21 of the TCS control module to pin 38 of the MOTRONIC control module and full-load enrichment is prevented, regardless of the position of the main throttle butterfly.

Checking Function
To check that "Disconnection of full-load enrichment" functions correctly, the following checks are carried out each time the car is started.
When the ignition switch is turned to the Drive position and also when the starter motor is in operation, the MOTRONIC control module sends an engine temperature signal to pin 11 of the TCS control module.

The TCS control module answers by sending a 31 Hz control signal via the cable for disconnection of full-load enrichment to the MOTRONIC control module.

If the MOTRONIC control module does not receive this signal from the TCS control module, diagnostic trouble codes will be generated in the MOTRONIC system.