I joined this group awhile back to look for answers, but I think I've got it figured out & wating for a diode from overseas to repair my SRS module. The 'answer' applies to ECMs too, so this will be worth the read.

I got a new battery for 'Betty' bc it was 6yrs old & getting weak, as its our 2nd car & I only start it once a week or so or to run the AC, etc. I washed pollen & crap off it & checked lights etc, but forgot to turn them off. A full 24+ hrs passed. Next day I was going to claybar the hood & polish w a new DA polisher so I went to start it like I always do & got no dash lights, etc. Realizing my mistake- leaving the lights on, I used my digital charger & Volts registered zero, with a clamp image like it wasn't hooked up. It was as dead as a battery can be. I got my old 1970s Sears analog charger & got it charging & in several hours I was able to start it. I let it run & ran the AC a few minutes as usual. As i turned it off I thought I noticed SRS lamp was on but wasn't sure & never had a reason before to think about SRS lamp & how it's supposed to act.

A few days later we got record snowfall (Houston TX) which collapsed the new popup canopy I'd placed over it the week prior. After weather cleared I removed the canopy & started it again, ran the HVAC, etc as usual, but when I shut it off I thought I noticed the SRS lamp was on again, but I don't usually pay attn to it so wasn't sure. I remembered the last time I thought I'd noticed it too but wasn't sure. The canopy collapse did bump it, but there wasn't a dent or anything & I thought it's unlikely that set off the SRS since it was sitting without a key in the ignition for days when it happened. I have the Helms shop manual so looked up SRS. I turned the ignition on & noticed the SRS lamp went off after the 6 seconds, but it came right back on & stayed on. I pulled the SRS DTC codes: 5-1 (bad SRS module) +2-3 &1-3, indicating 'short to power' on BOTH airbags. Manual says to test & repair the 2-3 & 1-3 codes before testing the module for 5-1 code to determine if its the harness or the module. It didn't make a lot of sense that BOTH would have a short to power & I didn't have the test harnesses anyway, so I would have had to remove the SRS plug & open the plug assembly casing behind it to test values directly without the harnesses. I cleared the MES & the SRS lamp stayed off until the next time I turned on the ignition, like it's supposed to. Turned it on again & the SRS lamp came back on like before so I rechecked the DTC codes again, getting the same results. I cleared the MES again -got the 2 blinks, but the lamp flickered & came right back on. It's not supposed to come back on until you shut it off & turn the ignition back on. I walked away from it for a couple days to study the manual & look online. Next time I checked the codes & got the same codes. I cleared the MES again- 2 blinks, but there was a nanosecond flicker of the lamp & it stayed on. My experience as an electronics tech told me the issue HAS to be in the SRS module, probably in the power supply circuit, as that's the most likely reason BOTH airbags have a 'short to power.' Plus, the MES wasn't operating right, confirming an issue in the module itself.

Online, someone mentioned having Main relay issues & the SRS lamp: that a shared circuit might lead to the relay getting power via one of the SRS fuses & confirmed the issue was indeed a blown pump fuse on theirs. I checked all the related fuses & they're all good. I decided the best course was to remove the SRS module & inspect for obvious problems on the PCB. I did the safety procedures on both airbags, swapping the red plugs, etc. B4 removing the module, I checked DTC codes again, this time I got 5-1, 2-1 & 1-1- because they were shorted for safety protocols. Cleared MES again & the same thing- 2 blinks to confirm, but lamp flickered & came right back on, which is not indicated in the manual at all, further confirming an issue in the module.

With the SRS module removed & on my workbench I put an antistatic grounding strap on my wrist & removed screws holding the cover on. Everything looked perfect, except for a diode that looked 'fluffy' on both ends. Inspecting with an eye loupe it appeared to have bits of the ceramic bead coming off of both ends. I removed the screws holding the PCB in the case, clipped my strap to a ground on the board & carefully inspected it more fully on both sides There were no hot spots or obvious issues other than the diode.

Being careful to not touch the ICs or introduce static voltage by using the grounding strap I carefully removed the diode. Using a low wattage soldering iron with pinpoint tip I removed the diode to test it. It tested OPEN in both directions "OL" using both Ohms & diode functions on 2 different DMMs. In both reverse & forward bias it had infinite ohms, or 'open.' In other words 'blown,' not shorted.

So, what blew the diode? Was it the charger? Not likely. Ignition was off & alternator working fine, so it wasnt backfeeding through the alt circuit -which wouldn't have reached the SRS or ECM with the ignition off anyway & a short via the wiring would have fried a fuse at the very least. Answer: 32 YR OLD CAPACITORS! Yes, those little cans with xxvolts & uF markings are DC caps. The 'back-up' batt inside the module is a capacitor - a special type called a 'dummy-lug' as caps hold a charge & in the case of power being cut during an accident the SRS module still needs to fire the airbags.

The module has about 10 capacitors in it, with a small brown one adjacent to & in circuit with the bad diode, with the 'Batt' cap nearby. There are 2 large orange caps - likely one for each airbag & a handful of others scattered around the power supply area of the PCB. Capacitors have electrolyte fluids in them. They eventually dry out or the electrolyte corrodes the aluminum plates inside creating a gas & leaking, either through the scored tops which open up or it pushes the rubber seals out on the bottom allowing it to leak. Given that the module was manufactured in '93, they're all at least 32yrs old. Where possible, using a bright pen light & eyeloupe I could see light from the underside of the caps shining through to the other side, except for the brown cap next to & in circuit with the bad diode. The caps are installed very close to the board, but I could see the black rubber on this cap was touching the board, so it's swollen, as the rubber seals aren't supposed to be pooching out proud of the cap like that, otherwise the light would have passed thru to the other side underneath it. Any 32 yr old cap is suspect & can fail at any time without cause due to age, especially in a hot environment like Houston. This is one reason why I'm not keen on getting a module or ECM from a junkyard, as they'll be just as old as mine are. Besides, at 64 with chronic pain & spinal arthritis I'm too old for that crap.

As for the diode, I didn't have any luck finding an exact electronic replacement for it locally. It's an 'ultrafast' avalanche diode & I know from experience that installing a 'replacement' semiconductor based on cross-reference guides is problematic. (Decades ago I suspected & replaced an old proprietary Harmon Kardon transistor in a receiver amp with the recommended replacement 'ECG123A,' which 'worked' but the amount of noise was atrocious. Thankfully the HK OEM was good & reinstalled it.) The ultrafast switching is needed in the SRS to scan the circuit & deploy the airbags in a timely fashion. I looked online for weeks & found exact FE5D diodes made by Vishay etc, but the look of them didn't impress me compared to the OEM 'GI' made by General Instruments in the US back in the day. Plus, it would take several weeks for it to arrive from either India or China & I didn’t feel confident about giving my credit card info over to their ordering platforms. None were available locally & or in the US as far as I can tell after wasting a lot of time emailing & calling distributors in the US, most of whom didn't bother to respond. I finally found some new old stock FE5Ds from an ebay seller in Italy - made by GI in 1988- selling them in quantities of 5, which are set to arrive no later than May 19. I am stoked about finding an OEM exact replacement for my diode! (lucky the ID marks on the blown diode were still readable)

The caps should be available locally, perhaps with the exclusion of the dummylug cap. I intend to replace all of them that I can find an exact electronic match for in volts & microfarads. The case shape & sizes are less of a concern & likely are smaller now than anyway & I can easily run circuit to accommodate any mods. I
Fingers crossed, this should fix my SRS module.

I've had intermittent issues w the main relay the last couple years- presumably related to how long it sits before starting it. 15 yrs ago I removed it & reflowed the solder on the pins (former electronic cal, mod & repair tech 1977-1990). As a 2nd car it sits mostly undriven now & sometimes takes awhile for the relay to click & the fuel to prime which turns off the check engine lamp. I removed & reflowed the solder a few months prior to the new batt, but intermittent relay issues remained after & there was no sign of cold solder joints when I reworked them (I'll come back to this later).

With the SRS module removed I started it & let it run with AC on etc & noticed both the SRS & Check Engine lamps stay on. When starting I always listen for the fuel pump prime, then the main relay clicks, the MIL lamp goes out & then I crank it. After removing the SRS module I switch it on, hear the pump & the relay click & wait for the MIL lamp to go out, but that doesn't happen. I realized 'hey that's probably because the SRS module is removed, dummy' so I cranked it & it started & ran normally. Time will tell if the relay behaves better after I replace the SRS module. I may even buy a new relay *gasp* LOL.

I may eventually remove the ECM to replace the caps in it too, because other than bad relay points in the Main relay itself, the most likely cause for it to act squirelly is caps in the ECM. Other than that small detail, everything works great, runs great, etc. If you look online there are people selling replacement cap kits for ECMs. It's not that well known, but in the late 90s & again in the mid 2000s there were epidemics of bad TVs, PCs, & other electronic devices because the circuitboards all had one or more defective caps on them. Bought in bulk at the cheapest price points, manufacturers installed these bad caps in their products. They failed within 6-18 months. Most of the runs of bad caps were made by a handful of companies. I've read stories about counterfeit HV caps too. It's possible that a bad or contaminated batch of the electrolyte was purchased & used by the cap manufacturers who had those bad runs, as not all the caps made by them at the time had this problem. If you do a little research online you'll see what I mean. Automotive products containing caps will fail eventually because of the physics of electrolytic caps. Keep this in mind if you have odd or intermittent 'roaming' issues that 'may be' the ECM.

Other Notes: Online, people were talking about having to use a torch to release loctite or plastic threads on the 4 torx bolts securing the module to the frame, so I was anticipating difficulty. Getting the plastic covers off was irritating, mostly because of the blind approach & not knowing how the covers connected & trying to avoid damaging them. Once removed I had no problem removing the torx bolts, probably because I used a 3/8" torx socket & ratchet with an extension & not a screwdriver wrench. They were tight, but no match for my ratchet. Similarly, people online complained about difficulty removing the bolt for the Main relay behind the hood release too which wasn't difficult for me. Perhaps as a woman, my smaller hands made it easier.🤷‍♀️ I think using the right tool is the main takeaway. At 64yrs of age, I've got 'all' the tools, so I grab any that seem appropriate, throw them in a bin & try what seems like the best option until I find the ones that work.

"Fluffy" looking diode on SRS module PCB. Brown capacitor at anode end is in circuit with it & at 1st glance looks fine, but rubber is swollen underneath. Larger round cap on the right serves as the 'backup batt'

Close-up of fluffy diode, tests open in both forward & reverse bias, ie 'blown'