DSA System Overview

Overview
General





The DSA control module has an integrated diagnostic system, the Volvo on-board diagnostic (OBD) system. This system continuously monitors itself and the input and output signals.

Diagnostic trouble codes (DTCs)
A diagnostic trouble code (DTC) is stored and the DSA warning lamp lights if the control module detects a fault. The exception is diagnostic trouble code (DTC) DSA-122 DSA warning lamp. This DSA warning lamp cannot be activated if this fault is stored.

Faults, with the exception of diagnostic trouble code (DTC) DSA-122DSA warning lamp, disengage the DSA function. If diagnostic trouble code (DTC) DSA-122DSA warning lamp is stored, the warning lamp cannot be used to determine whether the DSA function is engaged or not. The DSA function is then always engaged and cannot be disengaged manually.

If the DSA warning lamp is lit, the DSA function is not operating normally or it is not engaged.

If a fault disappears for any reason (becomes intermittent) after the diagnostic trouble code (DTC) has been permanently stored in the control module, information about the fault remains in the control module.

Other
Every diagnostic trouble code (DTC) has a counter. The counter records the number of fault-free cycles since the diagnostic trouble code (DTC) was stored (intermittent fault). A cycle is defined as the first time the engine speed exceeds 600 rpm in the same interval in which the ignition is switched on (the engine starts) and then switched off. If diagnostic trouble code (DTC) DSA-22 1 Load signal is stored permanently, the cycle is defined as the first time the average wheel speed exceeds 50 km/h in the same interval in which the ignition is switched on (the engine starts) and then switched off. When a counter is at 0, the control module interprets the fault as permanent. If the counter value is greater than 0, the control module interprets it as no fault (intermittent fault). If the fault recurs, the counter is reset to zero. When the counter reaches 254 (i e. 254 fault-free cycles), the counter is no longer updated.

General
Function in the dynamic stability assistance (DSA) antiwheel spin system

the DSA system assists the driver in holding the vehicle under control under (hard) acceleration, especially when the road surface provides less grip than the driver anticipated.

It also makes progress possible in very slippery conditions, which would not otherwise be possible without dynamic stability assistance.

Unlike the SRS-, ABS- or SIPS-systems, the DSA system is not a safety system. It is an aid to improve control of the car.

The DSA system can be switched off, but is automatically engaged every time the ignition is switched on.

A warning lamp in the dashboard indicates the status of the DSA system.

The DSA system consists of a single control module. This control module calculates wheelspin in the driven wheels from the information about the speed provided by the ABS control module. From this information the DSA control module calculates the torque reduction that is required. This information is transferred to the engine control module (ECM) which decreases the torque on the driven wheels to the normal driving conditions.

The DSA control module does not have sensors of its own. It uses the ABS system or engine control module (ECM) sensors.

The DSA control module can be activated at all speeds, both when the car is moving forwards and when it is moving backwards.

There are no functional similarities between the DSA system and the TRACS system.
- The TRACS system uses wheel braking to prevent wheelspin in one of the front wheels when the car moves off.
- The DSA system decreases the engine torque to prevent wheelspin on one or both of the driven wheels in all driving conditions.

System function





The DSA system must take account of any deviations caused by the steering wheel.. It is therefore important that no incorrect data is introduced by the system itself and that it goes through a number of stages before the torque reduction is activated.
- When the DSA control module detects wheelspin it first determines the extent of the spin.
- The average spin of the two front wheels is calculated. Differences in wheel speed because of cornering is compensated using sensors on the rear wheels.
- Information about the engine speed and load comes from the engine control module (ECM). The torque required from the engine is calculated from this.
- The selected gear can be derived by comparing wheel speed with engine speed. From this the friction coefficient between the tire and road surface can be deduced.
- Acceptable spin can be deduced from the accelerator pedal (AP) position and the friction coefficient.
- The engine control module (ECM) decreases torque by disengaging the injectors, so preventing wheel spin.

The DSA control module only sends information to the engine control module (ECM). It is this that close the fuel injection. The engine control module (ECM) can control the injection by closing the injectors, so that one or more injectors can be closed every 4th cylinder compression. It reduces torque in 16 stages.
- Partial closure of the injectors occurs randomly to ensure that the heat is evenly distributed.
- If the torque reduction is very small, a safety program is activated. After a given period the DSA shuts off several injectors (greater torque reduction) to ensure that the combustion chambers are correctly ventilated.
- The DSA system functions up to maximum. It is also active while reversing.
- The DSA system aligns itself so that it is does not identify different wheel diameter as wheelspin, in cases of variable tire pressure for example. DSA is not engaged if there is a slow puncture in one of the tires.
- Switch off the DSA system when driving on a "special spare tire". If not the system aligns itself to the diameter of the tire on the wheel. To assist this the car should be driven slowly, then accelerated hard for approximately 4 seconds. The accelerator pedal (AP) should be released quickly so that the engine brakes the car for approximately 4 seconds. Repeat this one more time. This procedure should be repeated when the special spare tire is replaced by a normal tire.

System overview





The DSA control module (1) needs data about the speed of all four wheels in order to detect wheel spin. This data is provided by the ABS control module (2). The data is transmitted continuously. The DSA control module is able to detect whether on or both of the drive wheels lose grip.

If wheel spin is detected, the DSA control module transmits a signal to the engine control module (ECM) (3) to reduce the torque. The engine control module (ECM) reduces the torque by shutting off one or more injectors (4) in different stages.

The engine control module (ECM) communicates with the DSA control module via three communication lines.
- The first communication line is used to transfer both speed (pulse frequency / one pulse per top dead center sweep) and engine load data. The engine load data is indicated by pulse width. Variations in the pulse width also provide additional data such as start, idling and transmission data.
- The second communication line transmits data about the position of the accelerator pedal (AP). A pulse is transmitted every 20th millisecond. The pulse is proportional to the given value.
- A third communication line is used for the transfer of data about torque reduction from the DSA control module to the engine control module (ECM). This pulse frequency is 5 milliseconds. Again it is the pulse width that provides the data.

The DSA system is switched on every time the engine is started.

The DSA system can be disengaged with the DSA switch (8) on the center console. The DSA system can be reengaged by pressing the DSA switch again. Otherwise, the system is activated the next time the ignition is switched on.

The DSA warning lamp is on the dashboard (5). This warning lamp indicates the status of the DSA system.
- The DSA warning lamp is lit for 2 seconds after the engine is started. During this time, the integrated DSA diagnostic system checks that both the ABS control module and the engine control module (ECM) are OK.
- The DSA system is not working if the DSA warning lamp remains lit. The is either a system failure or the system has been switched off manually.
- If the DSA warning lamp flashes while driving, the system is active and reducing the engine torque.

Diagnostic trouble codes (DTCs) from the DSA system can be read off with VIDA. Connect VIDA to the data link connector (DLC) (6) via VCT 2000.