Lotus Evora, Service Notes

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Page 8
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.