ECU Fuse Keeps Blowing after Trackday - No CEL - TT

JimmyK

They cover the bottom of my cupholder and I just ordered a few more for the tests so I don't deplete the kit, haha

Ah, at the very least that'll determine which line it is coming out of the IPDM, downwind from there I'm not sure I'll be able to get to everything, but it's a solid step. Worst case, I'll just tell a mechanic which line it was.

I'll also record live data from the ECU and scroll through that after it pops.

fryzia23

Have you replaced the relay? Bad relay could cause issues. It would make sense that after few mins of driving it gets so hot causing resistance and it spikes the amperage causing the fuse to blow. I think if other components were shorting it, I imagine it would throw some DTCs or cause drivability issues like misfires etc. you could also try disconnecting components and if possible go for a drive even in a limp mode and see if it keeps blowing the fuse. If it doesn’t then you’ll know it’s the component itself causing a short not the wiring.

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JimmyK

Hey fryzia, thanks for the reply!

Regarding the relay, in the PCS and PG sections of the FSM, there is not mention of the ECU relay being accessible. As far as I know it's internal to the IPDM, and may even be soldered to the board.

If the relay is inaccessible, I'll do a test on one of the sensors to see how well the voltage is doing. It was in range according to the ECU over OBD.

For the disconnected components, any recommendations as to what is less likely to harm the car? When I thought about doing this before, I chickened out because I thought I'd build too much pressure in the EVAP system without the EVAP Canister Vent Control Valve or the EVAP Purge solenoid, among other equally absurd reasons.

JimmyK

Still no luck, but hooked up ammeters to pins 49 and 53 coming off the IPDM Connector E7. Those go to most of the hardware, so if one spikes, or neither, it's likely to be 55, 69, or 70. I'll also record OBD data and post some screenshots.

Are we allowed to post screenshots from the FSM? I stitched together the ECU wiring diagram so its' easier to read and it'd be nice to post it and refer to it.

Also, here's hoping the line without the ECU spikes.

JimmyK

Hey all, not sure if anyone cares but in case someone in the future needs to know, I did find and fix the issue.

The harness was damaged around the passenger turbo area, it didn't have the appropriate shielding upon install from the kit manufacturer (before they were outsourcing to separate shops, so no blame to them). The primary retention method was plastic zip ties which all failed due to heat exposure, and the harnessing then came in contact with exhaust-magnitude temperatures.

The harness was patched up and the shorting was most likely the crankshaft position sensor or input speed sensor. Some other small repairs were made for stripped back shielding (that wasn't shorting but was in need of repair), and the harness wrapped and staked properly, with an additional heat plate installed for both shielding and structural support.

The job required a transmission drop to physically access the damaged area, in any other location it would have been easier (except for maybe underneath the manifold), so it was just bad luck that it required a ton of effort. All the searches did support me finding the issue, so it's worth the time and effort (bull) to figure out where it is only to find out that you can't fix it. Obviously I'm salty, but it was worth it and probably lowered the repair cost quite a bit since there was minimal troubleshooting required.

Car's back to normal now, can't wait to track it again! If anyone's interested in buying a low-mile and low-track use FI TT Z, feel free to PM. It's not up on the classifieds, yet.