SRS Diagnostic Functions
SRS diagnostic functions
General
The SRS control module has an on-board diagnostic (OBD) system, the Volvo on-board diagnostic (OBD) system. This provides self diagnostic and other information which can be read off using the Volvo Scan Tool (ST) connected to the data link connector (DLC).
When the ignition is switched on (ignition position II or engine running) the SRS on-board diagnostic (OBD) system carries out an initial self test. The SRS on-board diagnostic (OBD) system then goes into monitoring mode, carrying out a continuous self test on the system. The control module checks for internal faults in all SRS ignition cable outputs and in the output for the SRS warning lamp in the combined instrument panel.
Diagnostic trouble codes (DTCs)
If the control module detects a fault it stores a diagnostic trouble code (DTC) and the SRS indicator lamp lights light lights. The only time the warning lamp does not light is when the cable between the control module and combined instrument panel is short-circuited to ground or if the bulb is blown. When the ignition is switched on the lamp should light for approximately 3 seconds and then go out if no diagnostic trouble code (DTC) is stored. The control module can store up to 10 diagnostic trouble codes (DTCs). If for some reason a fault disappears after the diagnostic trouble code (DTC) has been permanently stored in the control module, information about the fault remains in the control module.
Each diagnostic trouble code (DTC) has 4 fault clocks which store data about the start time and, if applicable, the end time for the fault. Absolute start and end times are related to the total time that the system has been powered up. Relative start and end time displays the time the fault occurred or disappeared the last time the ignition was switched on. The absolute time displays the days and the relative time displays the hours, minutes and seconds. If the fault recurs, the end time is rest and the fault code counter (counter 2) counts up by one.
Each diagnostic trouble code (DTC) also has a counter (counter 1) which displays whether the fault is active (permanent) or passive (intermittent). If the counter value is 0 the fault is intermittent. The counter is used during fault-tracing to check if the fault has disappeared or if it remains. The diagnostic trouble code (DTC) status row is updated continuously and switches to intermittent fault if the fault becomes inactive. However, if the fault was passive, but then changes to active, the fault code status row changes to permanent fault.
Reading off the Volvo on-board diagnostic (OBD) system
Fault data and other information can be read off using the Volvo Scan Tool (ST) connected to the data link connector (DLC) under the center console cover. The Volvo Scan Tool (ST) communicates with control module via a standardized interface.
Using the Volvo Scan Tool (ST) it is possible to:
- read off and erase stored diagnostic trouble codes (DTCs), counters and frozen values.
- read the values and status of the system input and output signals.
- read off the control module identification.
- reset the system (corresponds to switching the ignition off/on).
Connecting the Volvo Scan Tool (ST)
Carry out the following to connect the Volvo Scan Tool (ST):
- ignition off.
- install the memory cassette.
- connect the Volvo Scan Tool (ST) wiring to the data link connector (DLC). This is located under the center console cover.
- ignition on.
- power up the Volvo Scan Tool (ST).
- select language, car and group of functions and the relevant system using the multi-function menu.
- select a specific function from the multi-function menu.
- select DIAGNOSTIC TEST to read and erase diagnostic trouble codes (DTCs).
- select MONITOR TEST to read off the values and status of the control module input and output signals.
- Select READ CM: ID to read off the control module P/N.
Reading and erasing diagnostic trouble codes (DTCs)
Stored diagnostic trouble codes (DTCs) and counters can be read off and erased using this function. The on-board diagnostic (OBD) system can identify 10 different faults in the form of diagnostic trouble codes (DTCs). For a list of diagnostic trouble codes (DTCs) and fault-tracing, see SRS Diagnostic Trouble Code (DTC) table Supplemental Restraint System (SRS).
Diagnostic trouble codes (DTCs) cannot be erased until all the stored DTCs have been read at least once during an ignition on interval, and the status of all DTCs is intermittent.
Internal diagnostic trouble codes (DTCs) cannot be erased.
Diagnostic trouble codes (DTCs) may be stored for the following faults in the airbag modules / seat belt tensioners:
- short-circuits.
- open-circuits in the circuit.
- short-circuits to ground.
- short-circuits to supply voltage.
Diagnostic trouble codes (DTCs) may be stored for the following faults in the SRS warning lamp circuit:
- open-circuit or short-circuit to ground.
- short-circuits to supply voltage.
The parameter values (status or frozen values) are stored for the following:
- warning lamp status.
Reading off the control module identification
The Volvo Scan Tool (ST) identifies control modules by reading a code from the memory of the module. This code contains information about the control module P/N.