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I recently had a short happen to me when I was looking at a broken plastic clip on the ECU housing. I was just trying to get the part # to replace it, so I wasn't expecting to work on the car and need to disconnect the battery.
When I rotated the ECU to see the back of the cracked plastic part on it, a piece of the metal enclosing the ECU hit the positive terminal on the battery and caused an arc, and now the car won't start. I can get into accessory mode and see the display on the dash and radio screen, but no ignition when I hit the starter. I checked the main fuse box and they're all fine, except the starter fuses. There's no power going to them, so I thought it was either a linkable fuse blew, or something in the pre-fuse box.
I tested the continuity at various points on the battery, and the ones indicated by either ends of the green line in the picture below were good (so the pyro fuse is fine), but the one in red was not. That leads me to believe that the fuse in the middle cream colour resin is blown.
I tried to bypass it by attaching jumper cables from the positive terminal to the far end of the pyro fuse (as indicated by the blue path in the picture), but the car still wouldn't start, so I'm thinking there could be something else keeping the car from starting, apart from the fuse on top of the battery. I also checked the continuity on the high amp pre-fuses coming up the side of the main fuse box, and they were OK.
Any ideas on what else I could check to see why the car won't start?
Edit: I also tried pulling out the box to the left of the battery with the thick red cables coming out of it (pictured here) and opening it up to test the continuity on the 3 fuses inside (pictured here) and they were OK too.
Last edited by Pyronaut; Dec 10, 2023 at 07:11 PM.
Hi, I hope this helps. From your detailed inspection and attempts at bypassing the blown fuse, it seems like the fuse you mentioned could indeed be the primary issue causing the car not to start after the arc incident. However, if bypassing it didn't resolve the problem, it's possible that there might be additional damage or another related issue affecting the starting system.
Considering you've checked the main fuse box and other relevant fuses without finding any issues, here are a few additional troubleshooting steps you might consider:
Battery Voltage: Ensure the battery is fully charged and maintaining adequate voltage. Even if the accessories work, the starter might not receive enough power to engage.
Ignition Switch: Test the ignition switch to ensure it's transmitting power to the starter. A faulty ignition switch could prevent the signal from reaching the starter.
Starter Relay: Inspect the starter relay for any signs of damage or malfunction. You can swap it with a similar relay from another function for a quick test.
Starter Motor: Check the starter motor for proper operation. If possible, you might try jump-starting the car to rule out issues with the starter.
Security System: Some vehicles have an immobilizer or security system that can prevent the car from starting after electrical issues. Ensure the security system is not engaged or interfering with the starting process.
Diagnostic Trouble Codes (DTCs): As you've rightly mentioned, using a scanner like the youcanic scanner to read any fault codes might provide specific information about other potential issues that aren't immediately visible.
If these steps don't yield a solution or if you're uncertain about certain components, it might be best to have a professional mechanic or technician perform a detailed diagnostic assessment. They'll have access to more advanced diagnostic tools and expertise to pinpoint the exact cause of the starting issue.
Because your car has so many electronics on it, it needs a functioning alternator. I agree with Vin 16, you need to take your car to a qualified mechanic who can properly diagnose and fix the problem.
Because your car has so many electronics on it, it needs a functioning alternator. I agree with Vin 16, you need to take your car to a qualified mechanic who can properly diagnose and fix the problem.
If the car won't start, how do I check the alternator? Doesn't checking it usually entail starting the car and checking the voltage that it sends to the battery?
Taking the car to a mechanic will be tough because it won't start so I'd have to tow it, and I also can't put it neutral to get it on a tow truck (electronic shifter), so I'm trying to do everything I can to check things myself before that point.
If the car won't start, how do I check the alternator? Doesn't checking it usually entail starting the car and checking the voltage that it sends to the battery?
Taking the car to a mechanic will be tough because it won't start so I'd have to tow it, and I also can't put it neutral to get it on a tow truck (electronic shifter), so I'm trying to do everything I can to check things myself before that point.
It's probably likely that you've also fried your alternator with the original incident. I think this situation needs to be evaluated by an experienced mechanic. If you belong to AAA, you can have your car towed for free to a garage that's 5 miles or less from your home.
I turns out that it was the ECU that was fried (see picture below). Multiple people who work on ECUs told me that it should have been fine from what happened, but I guess I had bad luck on this day.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
