Hi all. Long time, no post. I have an '09 Pontiac Vibe GT (or, Toyota Matrix XRS) 2.4L with a strange issue.
The 10amp (ECU-IG NO. 2) Back-up lights, charging system, rear window defogger fuse blows when I turn the key “on”, but sometimes shortly after it is started. It blew yesterday while I was driving (or I just noticed it while driving, may have blown on startup) and now blows consistently.
Oddly, this happened about a year ago and simply replacing the fuse worked, but not after I needlessly replaced the alternator and messed around with the neutral position switch and disconnected/reconnected some stuff down there (Had a related P0705 Transmission Range Sensor Circuit Malfunction code and the alternator was only charging at 11.7 volts - both of which were resolved with a new fuse.)
My guess now is that I accidentally “fixed” it back then by messing with the neutral position switch. I should mention that I recently replaced my radiator, which required a lot of knocking around in the tranny area, but that was about a month before the fuse blew.
I couldn’t find any damaged wires or loose connections around there (or anywhere else).
The fuse in question is also associated with the charging system and rear defogger, but I disconnected the low voltage alt cable and the defogger switch in the dash, and it still blew.
Any ideas?
Thanks in advance,
Jonas
A fuse blew in one of my pickup’s circuits. I cut every line before I found it was for the light in the glove box - which the pickup doesn’t have. (But the Forerunner does - uses the same harness.) I found no obvious problems. In other words I offer only a counsel of despair.
Sounds like you are going to need a wiring diagram and start looking at every circuit connected to that fuse and probably have to start with one circuit at a time and disconnect it from the end all the way back up to the fuse, that could include relays and module(s) etc…
And check ALL your fuses, OEMs do some crazy things sometimes…
I ended up taking my car to the shop yesterday, but now I’m a bit nervous. First, they called me yesterday afternoon to tell me they couldn’t find a blown fuse, even though I wrote down in detail where it was located. This afternoon, the last thing they were doing before they closed was performing a draw test. Does a draw test make sense for diagnosing a blown fuse? No one has suggested it to me.
Did you drive the vehicle to the shop? If the alternator fuse is blown, the alternator won’t operate, and the battery might discharge before you complete the trip.
I drove it over there. The alternator still kind of works, but it’s weird. The main fuse isn’t blown, but the blown fuse in question is associated with the charging system and some other stuff so the alternator only puts out about 11.7 volts for some reason.
I think that shop’s diagnosis skills may be weak
Most shops have weak electrical diagnostic skills.
It’s hard to diagnose an intermittent problem like this. Probably a wire is breaking and shorting out.
If it is currently shorted, you could supply a 10 Amp current limited 12V supply to the car or that circuit and then start probing around for Voltages. Voltage will drop from the resistance of the wire over segments of wire where the current is flowing. Look for small Voltage differences at different locations supplied by that circuit. If it is currently shorted the Voltage might be in the millivolt range.
If it’s not, maybe modify a fuse and put a 10 Amp PTC (resetable fuse) soldered to the top of a normal blown fuse that you cut the top off of. Then drive until the problem becomes constant or the wire breaks and some things stop working completely.
Perhaps the wire is now broken all the way and the alternator power has been cut off.
(Un)fortunately, the fuse pops consistently, usually when the key is turned to “on” or sometimes a few seconds after the engine is started. The reason I doubt their skills is that they called me a few hours after I dropped it off saying couldn’t find any blown fuse🙄 To be fair, the car will start and idle normally, but I did write them a note explaining where to find the fuse. I went back after hours and circled the fuse in the owner’s manual and left it open on the seat just in case lol
They may end up charging you as much as the car is worth messing around with it not knowing what to do.
Had a Ford Fusion I was taking care of. One day no crank because the theft system was triggered and the OBD II port stopped working. I said take it to a shop because it’ll take me days to get to the bottom of it and they’ll be upset with me for being slow. So it sat at the shop for a week and then they finally got to it. It was something like $150 for up to 2 hours of diagnostics or something like that. They couldn’t figure it out. The plastic was pulled up over the door sill where some wires go and the screws on the bottom of the cluster were out. I don’t they they really had any idea where to start.
I said no more and it was towed back. It took me a couple days and I had to purchase the wiring diagrams. A CAN bus wire going down to the electric power steering was broken down there. I was obvious since the CAN bus impedance was twice the spec. The ECU was disconnected from everything else, including the chip key reader.
In other words, you may have more skill for fixing this than your shop does. Is your time worth $200+ per hour?
I’m going to be extremely blunt
If the fuse pops consistently and the shop can’t figure out what’s causing it to blow, their diagnostic skills are TERRIBLE
You shouldn’t do business with them
You’re throwing your money away
I’ll bet you lunch ANY of the professional mechanics on this forum could figure this out in short order, if we were there with your car, along with a dmm and a wiring diagram
there are also “low tech” ways to help you find the cause of some shorts, such as plugging a sealed beam in place of the fuse in question . . .
Update
I thought of something else to check, so I walked to the mechanic’s shop, which is just across the street. Before I did anything else, I replaced the fuse to make sure it would still blow when I turned on the car, but it didn’t. I then started the car and the fuse still didn’t blow. So, I drove it home, no problem. There were some stored codes from before, but the live data looked good and everything worked. I don’t know what, if anything, the shop did, but the last thing I heard was they were “trying to get a draw on it.” I’d really like to know what was wrong, but I’m thinking about leaving well enough alone and just driving it. I’m also going to call the shop Monday morning and tell them about it. What do you guys think?
Nevermind. Fuse blew again.
I think they may have moved parts of the wiring harness around while looking for the short circuit, the short temporarily went away so they parked the vehicle. Perhaps later, the faulty circuit will “draw” excessive current at a later time.
The next time the fuse blew, was the vehicle in park, reverse or drive?
It blew while I was driving, in motion.
I also did a voltage drop test, (car turned off.) I couldn’t remember which probe went where, so I did both. Negative probe to engine block (positive probe to negative battery terminal), I got 0.3 millivolts. Negative probe to frame, the numbers kept changing, but would usually stop at around 50 millivolts.
Positive probe to engine block, I got 0 or -0.1 millivolts. Positive probe to frame, the number steadily climbed to 200 millivolts, read “OL,” then started over. What does this mean?
You need to find a better shop
These guys STINK
I think you’re right. I go to this place because they are walking distance from my house. They’ve done quality work before, but nothing electrical.
Well, maybe these guys are still okay for other things, but NOT electrical
If the fuse is blowing repeatedly and they can’t figure it out . . .
IF you’re using the type of blade fuse that has exposed terminals on top, then you can probe the Voltage across the fuse. If current is flowing through the fuse, you’ll see some Voltage on your meter.