Before starting fault diagnosis
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Before starting fault diagnosis
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Before starting fault diagnosis, always do the following:
Warning
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No tests or connections are to be made on the SRS before the airbags have been disconnected.
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Read through
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Switch off the ignition.
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Unplug the connector at the rear of the driver and passenger airbags. Unplug the 29-pin connectors underneath the front seats.
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Warning
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Splicing of SRS leads is strictly prohibited.
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Splicing can cause malfunctions which could render the system unserviceable and in the worst case lead to injury.
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Note
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If a connector is unplugged while the ignition is switched on, the control module will register it as a fault. This "fault" will persist until the connector is plugged in again and the diagnostic trouble code has been cleared or until 50 ignition on off cycles have been completed.
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General information on fault diagnosis in electronic systems
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Control modules
When current is applied to the control module, its processor is activated. The processor then reads the instructions that are stored in the control module's memory.
The control module is programmed to read inputs and activate outputs. If the control module's program is defective, an ”Internal control module fault” diagnostic trouble code will be generated.
Current must be applied to the control module before the system will work. It will be noticed when current is applied to the control module and the processor has been activated in that 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, e.g. an injector or a 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 the control module with correct values.
The operation of the sensors can be checked with the diagnostics instrument.
