Lotus Evora - Frontal Impact Sensing and Deployment; Fault Display

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Lotus Service Notes Section WF
tensioners.
• Incaseofarequireddeployment,timelyswitchingoftheactivationcurrentforthedeploymentloops.
• Detectionofelectricalsystemfaultswhichmayinfluencethereadinessofthesystemtodeploy,orincrease
the probability of an inadvertent deployment by:
- continuous electrical monitoring of all deployment circuits (without any effect on the readiness of the
system);
- continuous monitoring of the supply voltage and the lamp circuitry (dependent on lamp driver activation
status);
- SDM self test;
- activation of a tell tale lamp in case of a detected system fault.
• Faultstorageand'Crashrecording'withinEEPROM('crashrecording':recording ofsystemparameters
{e.g. fault status in deployment events}).
• DiagnosticcommunicationusinganISO9141protocol.
Frontal Impact Sensing and Deployment
The SDM and the two forward crash sensors contain accelerometers which provide a nearly linear propor-
tional electrical representation of the acceleration experienced by the vehicle along the longitudinal axis. This
signal is amplified 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 in either
stage 1 or stage 2 mode, and both front seat belt pre-tensioners.
To enhance system reliability under normal driving conditions, an additional electromechanical 'safing'
sensor is included within the SDM 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
deceleration condition monitoring by the safing sensor occurs in addition to, and independent of, the crash
algorithm.
Note that 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:
• Oneormoretroublecodesrequiringtelltalelampactivationinthe'historic'and'present'conditionare
stored in the SDM's EEPROM.
• 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.
• 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.
• TheairbagtelltalewillnotbeactivatedduetoSRSwarninglamprelatedfaults.
• 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.