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Need Help 987 Cayman S

2563 Views 45 Replies 8 Participants Last post by  deilenberger
I’ve been hesitant about posting because I made such a stupid mistake and wasn’t really ready for the roasting but here we are. I managed to hook my new battery up in reverse, positive to negative and negative to positive. Initially all electrical pretty much worked but wouldn’t start. I could hear the starter engaging but not spinning. I changed the starter and same. Pulled on the wire coming from positive battery terminal going to the firewall and the car started with no codes and ran for 3 days without issue. Last time it cranked it ran for about 5 seconds and died. The fans stay on, locks and trunks open, no dash but it does recognize the key, windows and radio don’t work. When I connect the battery it arcs. Any insight would
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Also, since tugging on the firewall wire made a difference once I thought maybe it was a weak link. I pulled the box, checked all the fuses and threaded the post instead of the push on connection.
Hey Texas. You're not the first one to do that and you won't be the last one, no judgment. Describe the arc of the connection, a tiny almost imperceptible spark or something else? Are you a PCA member? They have technical resources you can access.
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The arc is pretty big, the connection will stick to the terminal. I’m guessing it has to do with the fans constantly running. I’m not a PCA member. Thank you for your response
I’ve been hesitant about posting because I made such a stupid mistake and wasn’t really ready for the roasting but here we are. I managed to hook my new battery up in reverse, positive to negative and negative to positive. Initially all electrical pretty much worked but wouldn’t start. I could hear the starter engaging but not spinning. I changed the starter and same. Pulled on the wire coming from positive battery terminal going to the firewall and the car started with no codes and ran for 3 days without issue. Last time it cranked it ran for about 5 seconds and died. The fans stay on, locks and trunks open, no dash but it does recognize the key, windows and radio don’t work. When I connect the battery it arcs. Any insight would
As was mentioned - you certainly weren't the first to do this. It seems not to be uncommon (not exactly common, but damn close to it..) It seems there is always some damage.
Also, since tugging on the firewall wire made a difference once I thought maybe it was a weak link. I pulled the box, checked all the fuses and threaded the post instead of the push on connection.
Can you take a photo of where/what wire you tugged on? And I don't quite understand "threaded the post instead.." - what "post"?
The arc is pretty big, the connection will stick to the terminal. I’m guessing it has to do with the fans constantly running. I’m not a PCA member. Thank you for your response
Sounds like a failed component somewhere.

Sometimes after this sort of incident, it can take a while before components start failing. That's what it sounds like. You're either going to have to make an investment in a diagnostics tool, or take it to someone with a diagnostics tool. If you feel competent to effect a repair once the cause is identified, I'd suggest buying a tool with Porsche specific software. Durametric, Foxwell (NT530) and others make such tools. These will allow you to try to communicate with various control modules in the car, and try activating them using the software. The modules, if you can't connect - that's a big clue. If you can connect and there are some stored codes in the modules - those are a big help in diagnostics. If you can connect to modules and use the software to monitor and activate some of the module functions, that can be helpful in tracking down the problem and what needs repair.

Right now - we know something is broken - but I wouldn't hazard a guess without more diagnostics info. The next step is yours..
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The post in the center of this has a slide on connection with a plastic clip that holds it in place this is the wire I tugged on and initially got a response. I said through the “firewall” but it’s actually right near the battery where the positive cable exits the frunk. Mine had rust on it so when I removed it to inspect fuses and connections I threaded the center post to and bolted the cables to it to ensure a good connection
Automotive wheel system Font Auto part Rectangle Engineering
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Thank you guys for your time and responses
Picture purely for attention. I had just clay bar and waxed the day before it went down
Wheel Tire Car Vehicle Sky
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I will also say that when the battery was hooked up reversed the fans came on as well. That relay could be hung up or just pure coincidence. I have access to diagnostic tools so I’ll wait and see.
The post in the center of this has a slide on connection with a plastic clip that holds it in place this is the wire I tugged on and initially got a response. I said through the “firewall” but it’s actually right near the battery where the positive cable exits the frunk. Mine had rust on it so when I removed it to inspect fuses and connections I threaded the center post to and bolted the cables to it to ensure a good connection View attachment 285510
I believe this is the 80A fuse. If the car has any electrics working - this fuse is OK..
(Top item in diagram)
I will also say that when the battery was hooked up reversed the fans came on as well. That relay could be hung up or just pure coincidence. I have access to diagnostic tools so I’ll wait and see.
The bottom item in the diagram. the fan controller is basically attached directly to the battery via the 80A fuse, so a reversed battery connection stands an excellent chance of damaging that controller.
Slope Rectangle Line Font Parallel


There are very few "relays" actually used in any modern vehicle. What used to be relays are now electronic switches, controlled by a computer circuit responding to inputs from various sources (like temperature sensors.) A relay might survive a reverse voltage situation - some of the solid-state switches won't. This sounds like the case in this situation.

Once you're connected to a Porsche diagnostics tool you should be able to access the blower control unit and determine if it failed. As to what's preventing it from starting? You should be able to determine that when connected to a diagnostics tool.
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I would think a decent scan tool would be quite helpful. I have the Durametric which is OK, but since it doesn't work on my Macan or at least do anything useful I wouldn't recommend it. I have an iCarsoft CR Max and it is useful for our Porsches and VW. Back to your situation, I'd be suspicious of your alternator. I believe there are regulator diodes that could possibly be toast due to the reverse current. Also if you have a voltmeter you might want to check the battery voltage. Good luck we all make mistakes on the road to success.
The battery checks out at about 12.5v. I would think, but could absolutely be wrong, if the alternator was bad it would still run but not charge. Could it possibly be fried and sending current in the wrong direction? I have access to several scan tools, my stepdad owns a diesel repair shop and I’ve used them before to clear codes I’m just waiting for him to get a little free time.
Yeah I agree, but immediately thought of the diodes. Kind of interesting that there isn't a crowbar of sort of circuit to shunt reverse polarity current to ground. I've repaired all nature of medical equipment when I was part of the proletariat and most devices had that protection. It will be interesting to see what codes are reported. I guess worst case scenario is the ECU, but it is odd that the car ran for a few days.
Crowbar would be such an inexpensive preventative measure. They don’t want people to service their own cars anymore. What I did was dumb and immediately hurt my pride. I’ve changed shifter cables, shifter, two window regulators, coolant system seal, full exhaust, radio head unit which took a lot of figuring out especially with the Bose system and lots of miscellaneous other things. Only to get my *** kicked by a battery.
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If the fans constantly run I wonder if that might be throwing the car into a mode to save itself preventing any starting. Just random thoughts until I get the scan tool here.
The battery checks out at about 12.5v. I would think, but could absolutely be wrong, if the alternator was bad it would still run but not charge. Could it possibly be fried and sending current in the wrong direction? I have access to several scan tools, my stepdad owns a diesel repair shop and I’ve used them before to clear codes I’m just waiting for him to get a little free time.
I rather doubt if your stepdad's tools would be a lot of help. It's unlikely these tools have the Porsche specific functions that dedicated tools (or tools with installable software) have. Go big and spring for a Foxwell NT530 ($160 or so with the Porsche software) - you'll find yourself relying on it in the future when you really want to know what's going on. It will be cheaper than replacing parts (like the starter) based on guesses or Internet suggestions.

The alternator can't put out reverse polarity voltage/current. It has rectifying diodes in it that convert the AC into DC. Those won't change in a manner allowing reversed polarity. They could open - causing lower current capabilities, or short - putting a large amount of "ripple" on the output from the alternator... (BTW - some history - I'm that old - a "generator" which used a fixed magnetic field could be caused to put out reverse polarity voltage by hooking up the battery backwards. Did that on my first car, a 1957 DKW 3=6.)
Crowbar would be such an inexpensive preventative measure. They don’t want people to service their own cars anymore. What I did was dumb and immediately hurt my pride. I’ve changed shifter cables, shifter, two window regulators, coolant system seal, full exhaust, radio head unit which took a lot of figuring out especially with the Bose system and lots of miscellaneous other things. Only to get my *** kicked by a battery.
"Crowbar" is a heavy-duty electrical device unsuited for a car. It's designed to limit current surges.

What can be used and is used on many automotive devices is simple diodes, two of them rated for the amperage the device consumes will do the job. They pass electricity in one direction and don't pass it in the other. Correctly installed reverse hookup of a device simply means it will never see the incorrect polarity. There won't be any damage.
If the fans constantly run I wonder if that might be throwing the car into a mode to save itself preventing any starting. Just random thoughts until I get the scan tool here.
Nah. That level of intelligence isn't built in. The fans can (and sometimes do) run with the ignition off, or when turning the ignition on - if the coolant temperature warrants they be on.

Get the code reader. Scan all the modules in the car. Report back and we can try to lay out a logical troubleshooting path that avoids the "fix by replacing parts" diagnostics (which can be a VERY expensive way to troubleshoot things.)
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The scan tools that he has are a few grand each and he said he would download the programs needed for my car. I’ve heard my fans run after driving and parked for a few minutes but from battery hook up cold and never shut off isn’t normal. I’ll definitely report back when I find something out.
The scan tools that he has are a few grand each and he said he would download the programs needed for my car. I’ve heard my fans run after driving and parked for a few minutes but from battery hook up cold and never shut off isn’t normal. I’ll definitely report back when I find something out.
I'll be interested in hearing about success with the tools he has - and what tools he's using. I do know from experience - the Snap-On tools are not particularly good for Porsche's even with their horribly expensive Porsche module. Price doesn't necessarily equal capability.

And my point on the fans was that the car wouldn't be programmed to protect anything (by not allowing engine starting) if the fans come on immediately with the key since this can be normal behavior of a correctly operating fan/controller.
I’ll definitely update. I know the one I’ve been using isn’t Snap on. I’m not sure it will work, only can hope. I’m not afraid to admit when I’m wrong. Honestly knowing I can buy my own that will work for less than $200 has me thinking, especially since I own the car. The fans don’t come on with the key it’s immediately when the battery is connected. The only thing that changes with key is the ignition unlocks.
I'd try pulling all the fuses in the fuse box. Then replace them one at a time trying to determine what module(s) failed.
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