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  • Dgriff created a new forum post in MGF/TF Pitstop
    Hi all,
    thought I'd add my experience re the ubiquitous SRS light staying on issue. I think we're all pretty much aware of the main issues of under seat connectors and wiring issues and steering Rotary Coupler affecting the test routine of the SRS system. I've had personal contact with my MGF since 2007, (2002 Model MGF) being the servicing mechanic and now owner and I can say it has been an intermittent issue forever. However now being 20 years old the issue went from an occasional fault to one of the SRS light permanently being on when driving. Fault Code 150C. So with a registration inspection coming up shortly I had the choice of inspection failure, removing the globe or sorting it. Pretty sure the inspector would figure the con job of a globe removal, so with it being a fairly important safety device I accepted the challenge of sorting it. The lead up to this point being the light on all of the time, had progressed from the warning light coming on if the vehicle was left in the sun and extinguishing with a subsequent restart when the interior cooled off in shade or a change in weather. Therefore my suspicions had me thinking there was a resistance change from the heat in the steering wheel area (Fault code indicated drivers side) and it had reached a point of complete failure. Either the Airbag itself was being affected by the heat due to its age or possibly a deteriorating rotary coupler circuit expanding and contracting with the temperature change had finally open circuited. Having disconnected the battery and powering down the vehicle I removed the centre console to access the SRS ECU plug as well as the Airbag from the steering wheel and the steering wheel itself. I checked the resistance across the airbag terminals and it seemed to be in spec (2.3ohms)...Ok as far as internet knowledge informed me. I turned my attention to the complete wiring circuit from the SRS ECU plug to the Airbag Plug. It gets a bit complicated here because the plug configuration is not particularly logical in its layout, certainly in a way that is difficult to describe here. There are what seems to be a series of small pin connectors for each device circuit and a mechanical system of opening contacts within the plug. I couldn't find any SRS logic wiring diagrams to understand so I concentrated on finding continuity end to end through the driver side circuitry in some shape way or form...and behold I had a reading of 8ohms through one of the pins. So the question...where was the resistance? Luckily this turned out to be an easy one. On the dash side of the Rotary Coupler is the stationary plug arrangement where the wiring loom connects before it runs through the ribbon and appear on the steering wheel side of the coupler and ultimately the airbag itself. A removal of this plug to check continuity back through the loom and also through the coupler must have cleaned these contact pins (no fault with coupler determined) so when I reconnected and retested, the resistance had disappeared and a reading of 0.7ohms measured. So figuring this was a step forward and there wasn't much else to check, I refitted removed parts, powered up, test drove and voila...No SRS light! Hope this helps anyone else deliberating over a pesky SRS light.

    PS - Usual warnings apply when in and around airbag systems, the main one being do NOT investigate or test SRS wiring with battery connected.
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  • Has there been any more progress with this topic?...just curious as it would seem to me to be quite a useful reference.
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  • Dgriff thanked the user David Aiketgate in the forum post, MGF Rear track inner bush/joint - How to replace
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  • Dgriff thanked the user David Aiketgate in the forum post, MGF Rear track inner bush/joint - How to replace
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  • Just digesting your last reply....So I gather by your message, there is a realistic real world chance of uncontrolled 12V finding its way onto that circuit? Out of curiosity are we talking an internal ECU situation or external? Can you not incorporate a test button with associated stop/go LED (or a globe needing more than 20-30mA to fire up) to interrogate the K line before attaching scanner to computer and from a wiring point of view, before the driver chip?
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  • Dgriff thanked the user pscan.uk in the forum post, MAC OSX compatibility
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  • Well, did some wiring checks...I wish I could say there was some logic to the erratic readings I got. High resistance short (3.5K ohms), open circuit to earth and then continuity returned, seemed to stabilise on 75ohms...?. Noticed I had continuity on a number of pins at the ECU. I need to chase a wiring diagram that I have buried somewhere to make some sense of it, mainly colour codes, but the scan tool is up and running. The culprit is a suspect K Line wire as it runs under the MEMS 3 ECU support plate NS passenger lip of engine bay. Continuity readings jumping around wildly while pushing and pulling on wiring in this area. Released trapped wiring and uncovered wrapping expecting to find damaged insulation etc on a number of wires. Cant say I found any external damage so I guess there is something amiss internally. With all the prodding and twisting it seems to have sorted my K line fault issues completely and I can interrogate all relevant areas of the ECU. I'm not saying its sorted but it does prove the working potential of a Monterey 12.1 MacBook Pro with Pscan installed. I will persevere and keep the thread updated as I go. Cheers to Pscan UK.
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  • Dgriff thanked the user pscan.uk in the forum post, MAC OSX compatibility
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  • Dgriff thanked the user cairnsys in the forum post, References values MEMS3
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