So, I disconnected the alternator, the switch for the defogger, and replaced the fuse. The fuse didn't blow with the car on, but blew right after starting. I also pulled the backup lights and everything looked good. I didn't know much about electrical systems, so I'm just giving a play by play.
Fuse keeps blowing, P0705 (Transmission Range Sensor Circuit Malfunction)
- Thread starter Jonas
- Start date
The problem isn't going to magically go away by replacing the fuse five times. The problem has gotten worse in the past year and to the point now the short instantly blows the fuse. This is for safety otherwise it could start a fire. I would stop replacing the fuse until you find the issue - It sounds like you need a mechanic who can diagnose electrical issues.
I remember the last time this happened, I disconnected some wires from the transmission and adjusted the neutral safety switch before I replaced the fuse (didn't even know a fuse had blown at the time). I wonder if I inadvertently "fixed it" by doing that. I also recently replaced the radiator, which required a lot of knocking around in that area. Can I rule out the charging system and the defogger, since the fuse blew with them both disconnected? Also, does anyone know where the backup light switch is on the transmission? Thanks again.
I agree. I have an appointment on Thursday, but I'm going to keep troubleshooting in the meantime.
@Jimmy_Russells is right, you need a diagnostician/mechanic that can put eyes one it and do a proper process of elimination and not this back and forth with well intended stabbing guesses by numerous people. Not something that lends itself well to be done by committee on the internet when even yourself have limited experience in the field. Constant popping and reinstalling fuses could be causing even more damage.
This is the kind of stuff that causes vehicle electrical fires.
This is the kind of stuff that causes vehicle electrical fires.
Something is back feeding onto that circuit, and causing the fuse to blow.
Might be worth while performing a voltage drop between the engine block and the battery negative post and the frame/body and the battery negative post. You might have lost the ground strap between the engine and the frame.
Might be worth while performing a voltage drop between the engine block and the battery negative post and the frame/body and the battery negative post. You might have lost the ground strap between the engine and the frame.
Not to diagnose a blown fuse but to see how much current is blowing the fuse. He can tell if there is a dead short or if something is just drawing a little too much juice, it could help him narrow down an area.
The reason I ask is that I don't have much confidence in this shop's diagnostic abilities. Yesterday, a few hours after I dropped it off, the receptionist called me to say they couldn't find any blown fuse, despite me writing them a note explaining where it was located. The last thing I heard this afternoon was that the mechanic was trying to do a draw test but couldn't for some reason, then they closed for the weekend.
OH, thats not confidence inspiring.
Ask around local Jeep or hot rod clubs for a guy who's good with electrical diag. Maybe BITOG members could make suggestions if you start a thread and post your location. Maybe in the electrical section?
Most flat rate shops want cut and dried component replacement with a clean book time. My concern is that tech has a parking lot full of cars waiting on him and will either throw a Hail Mary at it ("I did X, we'll just have to see") or fall back on "could not duplicate customer concern"
*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?
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?
I did the voltage drop test (car turned off). I couldn't remember which probe went where, so I did both. Negative probe to engine block (positive 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?
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Check your battery negative cable at both ends for corrosion (at battery terminal and at frame point connection.
Here's a trick, repeat the tests with a jumper cable between the negative battery post and a point on the frame, and also between the negative battery terminal and the engine block.
If the numbers improve, then that concludes that you have ground issues.
Here's a trick, repeat the tests with a jumper cable between the negative battery post and a point on the frame, and also between the negative battery terminal and the engine block.
If the numbers improve, then that concludes that you have ground issues.
I fixed it!
TLDR, Alternator field coil wire was shorting out against the valve cover, fixed with high temp tape and a new wire loom.
The wire that powers the field coil of the alternator runs through the fuse that kept blowing. It gets energized as soon as the car is turned on, unlike the backup lights and the rear defogger (which run through the same fuse), so I figured that might be it. I did a continuity test on the wire and got an intermittent, 'morse code' sounding beep as I moved the wire around. I lifted the wire up and got a steady beep. I couldn't see any bare wire, but the insulation was pretty scuffed where it made contact with the valve cover, as a lot of the plastic loom had broken off. I got some hi temp tape (forgot what it's called, kapton maybe?) and a new loom to insulate the wires. Checked and got continuity again, replaced the fuse, and off I went. I drove for at least an hour yesterday in three separate trips without issue. All the accessories work too. I suppose the fuse held for a while when I first thought it was fixed, just because the wire had been nudged and wasn’t quite making contact.
I went to pick up my key today and the receptionist said, "Here's your key. Have a nice day!" Didn't charge me a dime.
Not the best pics, but you get the idea
Before:
After:
TLDR, Alternator field coil wire was shorting out against the valve cover, fixed with high temp tape and a new wire loom.
The wire that powers the field coil of the alternator runs through the fuse that kept blowing. It gets energized as soon as the car is turned on, unlike the backup lights and the rear defogger (which run through the same fuse), so I figured that might be it. I did a continuity test on the wire and got an intermittent, 'morse code' sounding beep as I moved the wire around. I lifted the wire up and got a steady beep. I couldn't see any bare wire, but the insulation was pretty scuffed where it made contact with the valve cover, as a lot of the plastic loom had broken off. I got some hi temp tape (forgot what it's called, kapton maybe?) and a new loom to insulate the wires. Checked and got continuity again, replaced the fuse, and off I went. I drove for at least an hour yesterday in three separate trips without issue. All the accessories work too. I suppose the fuse held for a while when I first thought it was fixed, just because the wire had been nudged and wasn’t quite making contact.
I went to pick up my key today and the receptionist said, "Here's your key. Have a nice day!" Didn't charge me a dime.
Not the best pics, but you get the idea
Before:
After:
