Lotus 2004 Eleven Service Notes page 483

Lotus Service Notes
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Fault storage and 'Crashrecording' within EEPROM ('crashrecording': recording of system parameters
(e.g. fault status in deployment events).
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Diagnostic communication using an ISO9141 protocol.
Frontal Impact Sensing and Deployment
The SDM contains an integrated accelerometer which provides a nearly linear proportional electrical
representation of the acceleration experienced by the vehicle along the longitudinal axis. This signal is ampli-
fied and filtered to reduce unwanted electronic noise and to compensate for offset drifts. The filtered signal is
then digitized to provide an input for evaluation by the crash algorithm. As soon as the crash algorithm detects
that pre-defined thresholds have been exceeded, the SDM activates both airbags and both seat belt pre-
tensioners.
To enhance system reliability under normal driving conditions, an additional electromechanical 'safing'
sensor is included to ensure that the SRS is armed only when significant deceleration occurs. In order to
protect against undesired deployments in case of severe EMI, humidity or accelerometer fault, the decelera-
tion condition monitoring by the safing sensor occurs in addition to, and independent of, the crash algorithm.
Neither the seat belt pre-tensioners nor the airbags will be activated by the SDM as long as the diagnostic
mode is active.
Fault Display
The following conditions lead to a fault display in the form of continuous illumination of the airbag tell tale.
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One or more trouble codes requiring tell tale lamp activation in the 'historic' and 'present' condition are
stored in the SDM's EEPROM.
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One or more trouble codes requiring tell tale lamp activation in the 'present' condition only are stored in
the SDM's EEPROM, the condition of which is, or has been, 'present' in the current operating cycle. For
all faults requiring four consecutive incidents for a trouble code to be set, the 'present' condition and fault
display will be activated already after two consecutive events if the related trouble code has already been
stored in a previous operating cycle.
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Faults concerning the voltage supply (overvoltage/undervoltage) will lead to tell tale activation only until
the regular voltage range has been reached again (turn-off delay max. 5s after return from undervoltage
and max. 20s after return from overvoltage). There are no related trouble codes.
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The airbag tell tale will not be activated due to SRS warning lamp related faults.
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The tell tale will be activated immediately after entering the diagnostic mode, or on deployment of the
SRS.
Excluding the exceptions stated above, it is not possible to switch off the tell tale other than by resetting
the fault codes stored in the EEPROM. This is not possible after an airbag deployment - the SDM must be
renewed.
The following delays apply for the detection and display of faults. The delays apply from the extinguishing
of the tell tale, following the ignition switch on bulb check period:
1 to 5 secs - for external deployment circuit faults and overvoltage supply.
12 to 20 secs - for undervoltage supply.
up to 15 secs - for SDM internal faults.
The tell tale will be activated without SDM intervention in the following situations:
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the minimum voltage of 8.0 V has not been exceeded after switching on the ignition.
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the energy reserve (in SDM) has run low, which may be caused by supply voltages below 7.8 V.
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the watchdog has interfered.
A trouble code readout using tell tale blink codes is not implemented.
Power Supply & Grounding
The nominal supply voltage of +12 volts is derived from terminal 5 when the ignition is switched on. The
SDM internal ground (terminal 7) must be securely connected to the vehicle chassis ground. To provide
redundant grounding, the SDM housing is internally connected to the ground connector pin.
Supply Voltage Range
The SDM is designed to operate within the following voltage ranges:
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Section WD