Lotus Eleven/Elise/Exige. Manual - part 121

    

Lotus Service Notes                               Section WD

Page 11

Inspections Required After an Accident

All SRS system components, including harnesses and brackets, must be inspected after an accident. If

any are damaged or bent, they must be replaced even if a deployment did not occur. If the SRS was deployed,
the following components MUST be renewed even if there is no visible damage to the parts:
Driver airbag module;
Passenger airbag module;
Sensor & Diagnostic Module (SDM);
Driver and passenger pyrotechnic seat belt assemblies;
Rotary connector;
Passenger airbag mounting brackets (2);
Passenger airbag shute (2);
Passenger airbag door assembly (trim panel);
Dash panel upper extrusion.

Inspect the steering column for damage or telescoping (see Section HG) and column mounting brackets

for damage.  Inspect the chassis scuttle beam in the area of the passenger airbag mounting brackets for
damage or distortion.  Inspect the SRS wiring harness and connectors for damage or any signs of overheating.
Do not attempt to repair the steering column or chassis or any of the above mentioned components.  Service
is by replacement only.

WARNING:  Proper operation of the SRS system requires that any repairs to the vehicle structure
return it to its original production configuration. Deployment, or any visible damage to the SRS com-
ponents and/or their respective mounting brackets requires replacement, not repair.

WD.7 - THEORY OF OPERATION

The key components of the Supplementary Restraint System (SRS) are the following:

•

Sensor & Diagnostic Module (SDM);

•

Driver airbag module;

•

Passenger airbag module;

•

Rotary connector;

•

Seat belt pre-tensioners.

Sensor & Diagnostic Module (SDM)

The SDM is the main electronic control unit (ECU) of the SRS, whose function is to detect rates of forward

deceleration, and when interpreted as a collision accident requiring supplementary occupant protection, the
SDM triggers as a single set, the driver and passenger airbags and both seat belt pre-tensioners.  Additional
functions are to maintain an energy reserve in case of vehicle battery power interruption, operation of a dash
mounted tell tale lamp, and a electronic diagnostic and event recording facility accessible via a workshop
scanner tool.

The unit is mounted by a dedicated bracket to the top of the passenger side scuttle beam, accessible after

removal of the fascia top.

The following functionality is provided by the SDM;

•

Sensing of frontal impact crash events and vehicle specific discrimination between non-deployment and
deployment-requiring events as well as the deployment of the frontal airbags and seat belt pre-tensioners.

•

In case of a required deployment, timely activation of the activation current for the deployment loops.

•

Detection of electrical system faults which may influence the readiness of the system to deploy, or in-
crease 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.

    

Lotus Service Notes                               Section WD

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•

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 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.

•

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.

The tell tale will be activated without SDM intervention in the following situations:

•

the minimum voltage of 8.0 V has not been exceeded after switching on the ignition.

•

the energy reserve (in SDM) has run low, which may be caused by supply voltages below 7.8 V.

•

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:

    

Lotus Service Notes                               Section WD

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System fault detection, SDM self test: min. 8.0 V; max. 16.0 V
Below 10.0 V system readiness may be delayed by 3 s.
Below 9.0 V system readiness may be delayed by 10 s.
System fault detection and SDM self test are reduced as long as an undervoltage condition is detected, which
could already apply for supply voltages below 10.5 V.
Activation of airbags: min. 8.0 V; max. 16.0 V.
Activation of seat belt pre-tensioners: min. 10.0 V; max. 16.0 V.

Energy Reserve

Energy reserve capacitors within the SDM are provided to allow SRS deployment if the vehicle battery

power supply is interrupted during the time of vehicle impact.  The capacitors provide full support of the
acceleration sensing and airbag initiation capability for a minimum of 150 ms after a loss of external power
supply, provided that before the loss, the SDM had been supplied with:
at least 10.0 V for at least 10 s; or
at least 9.0 V for at least 13 s; or
at least 8.0 V for at least 20 s.

The capacitors will be discharged down to a point where no initiation of airbags is possible within a max.

of 20 s after removal of the power supply.

WD.8 - SENSOR & DIAGNOSTIC MODULE (SDM)

To Replace SDM

WARNING: The SDM must be replaced after SRS deployment.  Do not attempt to repair or reuse.

The SDM is mounted on a bracket riveted to the top of the passenger side scuttle beam, and is accessible

only after removal of the fascia (dash) top panel.

1.

Follow the safety procedure detailed in sub-section WD.6 to turn off the ignition, disconnect the battery
and unplug the yellow 4-way connector to the inflator module, alongside the steering column.

2.

Column shrouds:  Remove the two screws retaining the top part of the shroud, and the four screws
retaining the lower part, and withdraw both parts from the column.

3.

Instrument shroud:  Pull the instrument shroud backwards to release the four spring clips from their
apertures in the dash panel.

4.

Sill top trims:  Release the two screws at the bottom of the coin pockets at the front of each sill, and pull
the sill top trim panels from the chassis.

5.

Dash end panels:  Release the two screws within the top of each coin pocket, and withdraw the switch
panel (driver's side) and blanking panel (passenger side) from the dash end panel.  Unplug the wiring
harness from the switch panel.
From within the aperture, release the two screws retaining each end panel to the dash, and pull the panel
rearwards to withdraw the spring clips in the top of the panel from the dash.

6.

Airbag door:  Pull the airbag door away from the dash, which action will probably require the four retaining
clips to be renewed.  Note that the door is constrained by two tether straps.

WARNING:

•

The only permitted repair to the airbag door and tether strap assembly is the replacement of the
plastic retaining clips which secure the door to the dashboard.  If the clips are broken, they MUST
be replaced ONLY by the correct Lotus supplied parts.  Do not attempt to fix the door in position
by any other means.

•

After SRS deployment, the airbag door assembly MUST be replaced even if there is no visible
damage.

    

Lotus Service Notes                               Section WD

Page 14

7.

Centre vent panel and radio surround:  Release the two screws at each side of the panel and withdraw.

8.

Fascia top panel:  Remove the 5 screws securing the rear edge of the panel to the dash rail, and withdraw
the panel rearwards to disengage the two spigots from the base of the windscreen surround.  Disconnect
the speaker cables.

9.

SDM:  Unplug the harness connector from the SDM.  Release the four retaining nuts, and withdraw the
sensor and diagnostic module from its mounting bracket.

Refitment of the SDM is a reversal of the removal procedure, but remember to check that the tether strap

bracket for the airbag trimmed door has been secured before the fascia top panel is fitted, and that new push
fasteners for the airbag door will be required.  Use Scan 3 tool or Lotus TechCentre to configure airbag system.

WD.9 - DRIVER AIRBAG MODULE

WARNING:  Safety precautions must be observed when handling a deployed airbag.  After deploy-
ment, the airbag surface may contain a white packing powder used to ease deployment, together with
a small amount of sodium hydroxide dust, a by-product of the sodium azide reaction during deploy-
ment that can be irritating to the skin if left on for an extended period of time.  Always wear gloves and
safety glasses when handling a deployed inflator module, and wash your hands with a mild soap and
water afterwards.

The driver's airbag (or inflator module) is housed in the hub of the steering wheel, beneath a moulded trim

cover designed to hinge open in the event of deployment.  The module comprises:
-

an inflatable fabric bag;

-

an inflator (canister of gas generating material)

-

an initiator (or 'squib')
When the vehicle suffers a forward deceleration of sufficient magnitude to close both the safing sensor

and integrated accelerometer within the SDM, current flows through the deployment loop of both the driver and
passenger airbag module initiators and ignites the gas generating material.  Each bag inflates in a fraction of a
second, the driver's bag bursting open the steering wheel centre trim cover, and then deflates via vents in the
bag, with the whole cycle taking less than one second.  The airbag is designed for a single deployment, and
must then be renewed.

In order to help prevent unwanted deployment of the driver's airbag when servicing the steering column or

other SRS components, a shorting bar is incorporated in the airbag side of the 4-way harness connector plug
located alongside the steering column.  The shorting bar operates when the connector is unplugged, to short
across the feed and return connections to the airbag.  Thus, if a positive feed, or earth is inadvertently applied
to the connector terminals, both sides of the inflator module will be subject to the same electrical potential, and
no deployment will occur.

To replace driver's airbag

WARNING:  The following procedures must be followed in the order listed to temporarily disable the
airbag system whilst working in the immediate vicinity of an airbag.  Failure to follow this procedure
could cause unintended airbag deployment, resulting in personal injury and unnecessary airbag system
repairs.
a).

Turn off ignition.

b).

Disconnect the negative battery cable, and tape back to ensure that it cannot contact the battery terminal.

c).

From alongside the steering column, in the area of the column upper fixing, locate and disconnect the

driver's airbag yellow 4-way harness connector plug.

1.

Column shrouds:  Remove the two screws retaining the top part of the shroud, and the four screws
retaining the lower part, and withdraw both parts from the column.

2.

On the reverse side of the steering wheel, locate and remove the two socket head screws, accessible via
holes in the plastic shroud around the steering wheel hub.  Withdraw the airbag module and disconnect