Lotus Elan

Air bag problems

PostPost by: oldchieft » Mon Jul 21, 2014 8:48 pm

Hi all
I know this is not a topic for Lotus, but a lot of us have car with the unexploded bombs in our face that are quite old.

My Mini is 15 years and this has just raised its head at MOT.

As this forum has a better technical basis then any other I would expect the would be a lot of knowledge on fault finding on these.

Mine has a warning light come on, goes off, then comes on and stays on.

Mine is a simple system with three nodes, 1 x air bag, 2 x seat belt pre-tenshioners, and one control unit.

Basic start off advice would help.

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PostPost by: p.faurie » Mon Jul 21, 2014 10:17 pm

Hi Jon,a lot of problems with air bag warning lamps coming on with two door cars is the wiring connections under the seat for the pre tension ears, I don't know if that system can be read with diagnostic kit ,but I would have thought so,DONT go poking around under the seat until you disconnect the battery,undo and reconnect the connectors for the tensioners, reconnect the battery and start the car ,if you are lucky the light will go out,if not you'll have to get it plugged in
Good luck
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PostPost by: billwill » Mon Jul 21, 2014 10:51 pm

When you start an air bag car, the airbag computer tests that the detonators are connected by measuring a very low current, insuficient to set it off.

Because of the very low voltage, the ciruit is prone to contact pressure problems on connectors. Usually removing & reconnecting any plugs & sockets under the seat will resolve the problem.

DO NOT USE AN OHM-METER, the test current might fire the detonator.
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PostPost by: oldchieft » Tue Jul 22, 2014 7:37 pm

Thanks for the start,

I have got to the bottom of this, and I will post the steps.

1 Finds the plugs for all the units.

2 Disconnect the battery.

3 Pull off the plugs to the pre-tenshioners, and control unit.

4 Take the steering cowl off and find the connection on the fixed part of the rotator unit, and pull that plug.

You now have a dead system, and you can start to rebuild it, but you need some resistors to simulate the nodes.

5 Buy some 2.7 Ohm resistors from Maplins and put them into the the plugs.
IMG_1231.jpg and

IMG_1235.JPG and

The system is now set to simulate all the air bag and pre-tenshioners.

6 Spray the plug and socket to the control unit and plug it in, then connect the battery and switch on the ignition.

The warning light now works correctly, switch off and disconnect the battery

7 Add the pre-tenshioners one at a time spray cleaning each plug and socket, but switch off and disconnect the battery each time, WAIT 10 MIN AFTER DISCONNECT BEFORE MAKING A NEW CONNECTION.

8 Remove the air bag and re-make the connection at the fixed part of the rotator, move the resistor to the air bag plug at the moving part of the rotator.

9 This last test proves the rotating connection, if all is still working put back the air bag.

I my case the system had no faulty units, just bad connections.

I did not need to touch any unit with a test meter.

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PostPost by: reb53 » Wed Jul 23, 2014 6:07 am

Does the workshop manual give you any hint as to what that particular light sequence means ?

On my old Mondeo it pointed me directly to the pre-tensioners.
A replug of the connectors under the seat keeps the problem at bay for a few years.
Before I discovered this I put a small piece of black tape on the dash in front of the flashing fault light so as to get past my MOT.
The tester looked in vain for the usual "airbag" light on startup and not finding it decided the car didn't have one for some reason....

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PostPost by: oldchieft » Wed Jul 23, 2014 9:34 am

In the case of my mini I was able to find the manual online but it is omitting a lot of information.

It says: -
In the event of a fault in the system, the warning light will either:
1. Illuminatecontinuously;
2. Illuminate for 0.5second,extinguish,then
illuminate continuously;
3. Failtoilluminateduringtheselfdiagnosistest.
Fault diagnosis
Diagnosis is accomplished using TestBook connected to the vehicle diagnostic connector which is located on a bracket by the foot pedals.

While I had the system apart I tried open circuit and shorted on the air bag, in each case I got fault 2.

The is one wire showed on the wiring diagram to the diagnostic socket but the is no information about this in any manual, or on line that I can find anywhere.

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