General
The control module has an on board diagnostic system, Volvo Diagnostics. The control module continuously monitors itself and input and output signals in the system. By connecting the Volvo Scan Tool (ST) to the data link connector (DLC) it is possible to obtain different types of information in the form of diagnostic trouble codes (DTCs), current parameters for readings on components etc.
The diagnostics system can also be used to activate components and functions by using the Volvo Scan Tool (ST).
Note. If it is not possible to operate the seat or access the diagnostic system, check that none of the buttons on the control panel are stuck in the down position. Carry out the procedure again with the engine of the car running. Battery voltage must be at full voltage in order for the before the on-board diagnostic (OBD) system to work. See Checking supply voltage and Checking communication .
On cars within the chassis range 267000 - 273594 (4-door) and 171000 - 177545 (5-door) the control module's diagnostic functions have been disabled. The Volvo Scan Tool (ST) can only be used if the existing control module is replaced with a new module. The existing control module on the cars in these chassis number ranges operate normally apart from the disabled diagnostic functions.
On a few cars within the chassis number ranges the diagnostics wiring to the control module is disconnected. When replacing the control module with a new one the diagnostics wiring must be connected to connector A to the control module in order for communication with the Volvo Scan Tool (ST) to take place.
The control module is located underneath seat. The control module has a microprocessor and a number of relay functions, a dual relay for each motor and a main relay for the main power supply.
Seat positions are stored in an EEPROM type memory. This type of memory stores information indefinitely, even if there is no power to the control module.
Scheme 329
Power to the relays and electronics is controlled directly by the control buttons. When the seat is not being operated all power to the motors is cut to ensure that the seat stops moving.
If more than one button is operated at the same time, the seat will stop. The only motors which can be operated simultaneously are those controlling the seat cushion height.
If an open-circuit, short-circuit to ground or supply occurs in the leads to the motors or sensors, this will be detected when trying to operate the motor because the sensor signal will not change. The motor concerned is then disabled.
If a button is held down for longer than 60 seconds, the power is cut to the main relay.
This function is controlled by a timer circuit in the control module.
Scheme 330
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The power seat is available as a factory-fitted option. It can be installed instead of the standard seat on both driver and passenger positions.
The power seat has three memory buttons for storing three different seat positions.
1992-1995 cars have an earlier type of on-board diagnostic (OBD) system. See earlier service manual.
From 1996 models onward, an improved on-board diagnostic (OBD) system has been introduced, which is described in this service manual.
Refer to Diagnostic functions Volvo Diagnostics using the Scan Tool (ST) to see how to use the improved on-board diagnostic (OBD) system.
Note. When replacing the control module with a new module always check that the new control module has P/N 9174904 (left seat) or 9174905 (right seat). The earlier type of control module has a different type of diagnostics. The older versions operate correctly with the different seat functions, but their diagnostic system cannot communicate with the Volvo Scan Tool (ST).
The control module located under the seat cushion operates four different motors in all. Three of the motors are located under the seat, the fourth is located in the backrest.
The control module with memory receives information on the seat position from signals from four position sensors. These are potentiometers driven by a worm gear on the output shaft of each motor.
By connecting the Scan Tool (ST) to the data link connector (DLC) it is possible to read out information on possible faults in the system as well as get other information. The Volvo Scan Tool (ST) communicates with the control module via a standard communications interface.
Connecting the Volvo Scan Tool (ST) is described in Volvo Scan Tool (ST) .
Scheme 331
The data link connector (DLC) is located in the car.
To establish communication with the power seat control module the following conditions must be met
- Battery voltage must be more than approx 11 V.
The ignition can be turned OFF.
Activating components/functions
This function makes it possible to operate the seat using the arrow keys on the Volvo Scan Tool (ST).
Reading off input and output signals
This function makes it possible to read off the value on all the control module's inputs and outputs.
- Supply voltage
- The control module's relays (outputs to motors)
- The potentiometers values
- The motors' speed
- The buttons on the control panel
For more information refer to Volvo Scan Tool (ST) Scrolling values .
Reading the control module ID
The Volvo Scan Tool (ST) identifies control modules by reading a code from the control module memory. The code contains information on the part number of the control module and the software version it is using.
Scheme 332
The four motors control the following functions
- Motor 1 moves the seat backward and forward.
- Motor 2 controls the backrest angle.
- Motor 3 controls the height of the rear of the seat cushion.
- Motor 4 controls the height of the front of the seat cushion.
Potentiometers
The potentiometers (5) act as position senders and provide the control module with feedback information on the position of the seat. They are driven by a worm gear located on the output shaft of each motor.
The resistance in the potentiometer is proportional to the output shaft position.
Scheme 333
There are six control buttons - the seat squab control shaped like the seat squab, the seat backrest control shaped like the seat backrest and the four memory buttons.
Pressing more than one control or memory button at the same time will result in the seat coming to an emergency stop.
Scheme 334
- The control shaped like a seat squab controls the seat height at the front and rear and moves the seat backward and forward.
- The control shaped like a backrest controls the backrest angle. The lumbar support is adjusted manually.
- The three memory buttons, which are marked 1 , 2 and 3 are used to store and recall seat adjustment settings. To move the seat into a pre-set and stored position, hold a memory button down until the seat has reached that position. If the button is released while the seat is moving to the stored position it will stop moving immediately.
To store a seat position
- Operate the power seat controls until the seat is in the position required.
- Then press the programming button, marked MEM and keep it pressed in.
- At the same time press one of the memory buttons and the seat position is now stored in the control module memory.
The control module has an integrated diagnostics system, Volvo On-board Diagnostics (OBD). The control module continuously monitors its own functions and the input and output signals in the system. Various types of information can be obtained, such as the current values of read-off components etc., by connecting the VCT 2000 to the data link connector (DLC).
The on-board diagnostic (OBD) system also makes it possible to activate components and functions using a VIDA PC.
Note. If it is not possible to operate the seat or access the on-board diagnostic (OBD) system, check to see if a button on the control panel is stuck in the depressed position. Also try repeating the process with the motor running. Battery supply must be at full voltage before the on-board diagnostic (OBD) system will work. See Checking supply voltage .
On cars within chassis numbers 267000 - 273594 (4-door) and 171000 - 177545 (5-door) the control module diagnostic function is disconnected. The VIDA PC can only be used if the existing control module is replaced with a new one. The existing control module on cars within these chassis numbers normally functions correctly apart from the diagnostic function.
In a few cars within the above chassis numbers the diagnostic lead to the control module is disconnected. When installing a new control module the diagnostic lead must be connected to connector A (control module side) in order for communication with the VIDA PC to be possible.
Fault data and other information can be read off using the VIDA PC connected to the data link connector (DLC) via the VST 2000. The VIDA PC communicates with the control module via a standardized interface.
The data link connector (DLC) is located in the passenger compartment.
To activate communication with the seat control module the following conditions must be met
- Battery voltage must be above approximately 11 V
The ignition can be switched off.
This function allows the value of all the control module inputs and outputs to be read off
- Supply voltage
- Control module relays (outputs to motors)
- Potentiometers' values
- Motors' speed
- Control panel buttons
The control module has an integrated diagnostics system (the Volvo On-board Diagnostics (OBD)). The control module continuously monitors its own functions and the input and output signals in the system. By connecting the VCT 2000 to the data link connector (DLC), different types of data can be obtained, such as diagnostic trouble codes (DTCs) and the current values of read-off components etc.
The on-board diagnostic (OBD) system also allow components and functions to be activated using a VIDA PC.
Note. If the seat cannot be operated or if the on-board diagnostic (OBD) system cannot be accessed, check to see if a button on the control panel is stuck in the depressed position. Also try to repeat the procedure with the motor running. Battery supply must be at full voltage before the on-board diagnostic (OBD) system will work. See Checking supply voltage .
Control module
Control module
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Power seats are available as factory fitted options. Both driver's and passenger seats are available.
Three different seat settings can be stored using the memory buttons.
Note. When replacing the control module, always check that the P/N of the control module is 9174904 (left seat) or 9174905 (right seat). Old version control modules have differences in diagnoses. These can operate the various seat functions correctly, but the diagnostic system will not be able to communicate to VCT-2000.
The control module located under the seat cushion controls four different motors. Three of the motors are positioned under the seat and the fourth is located in the backrest.
The control module with memory receives information about the position of the seat via signals from four position sensors. These consist of potentiometers which are driven by a worm gear on each motors' output shaft.
Motors and potentiometers
Motors and potentiometers
Seat controls
Seat controls
Control module
Power seats are available as a factory installed option. They are available for both the driver's and passenger sides.
Three settings can be stored for the seat using the memory buttons.
The control module, which is positioned under the seat cushion, controls four different motors. Three of the motors are positioned under the seat. The fourth motor is in the backrest.
The control module and memory receives data about the seat position via signals from the four position sensors. This consists of potentiometers which drive a worm gear on each motor output shaft.
Motors and potentiometers
Seat controls