Keep blowing fuse 5
 

2001 X5, replaced head gaskets, everything was fine for 2 months, then shifted hard, wouldn't start. Found fuse 5 blown, replaced it, as soon as the car shifts, it blows the fuse again. Per information on other threads, checked oil level sensor, alternator wiring, and efan. No bare wires, shorts, etc. Fuse box says fuse 5 is Eng Control. Anyone had this problem, and how did you fix it? Any thoughts.


Thanks in advance

You have a short somewhere in the wiring circuit that pertains to transmission shifting. You are going to have to isolate the circuit in different places and test to make sure that wiring is sound in that area before moving to the next area. As a beginning step you will want to have the vehicle scanned to see what the codes are. Will have to erase them start the vehicle and then scan again for any new codes and then debug from there.

This might help. Maybe something is almost shorting and when the motor/trans moves on shift it touches.

• F5 (7,5A) Alternator, engine oil level sensor, fuse box/relay plate cooling fan motor
• F31 (5A) Engine management
• F54(15A) Transmission control module(TCM)

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Guess I should have said in the initial post that there's no codes. I've (as stated), checked the alternator wiring, oil level sensor wiring, efan wiring. Put the car up on a hoist and checked the wiring looking for bare spots/rubbing. How does fuse 5 come into play during shifting that would cause it to blow? It doesn't seem to have any interconnection with the shifting.

I don't know the answer - sorry. But to address your point "How does fuse 5 come into play during shifting that would cause it to blow? It doesn't seem to have any interconnection with the shifting."

It may well not be involved in shifting, but something else that is? maybe able to short out the F5 circuit. Have you had a good look at the actual shift lever for wiring damage caused by the movement of the lever itself?

Does the fuse blow immediately you attempt to move the lever or when it selects a gear 'D - N - P - R' etc. Does it do it in Sport (or before you get that far? This may help to understand if it is the shifting action or the gearbox response that causes the fuse to fail.

On a previous X5 I owned somebody had attempted to chop into the loom to hook up a camera (I think) this had the result of truck occasionally refusing to shift of shifting up when I selected down etc. I recall reading of another case on a Mercedes forum where somebody had dropped coins down there and they were causing strange issues. Fizzy or sugary drinks are another thing to check out for, best removed with electrical switch cleaner. Good luck.

What code scanner are you using? My recent experiences show huge differences between scanners in terms of what they actually see and how much use they are. My icarsoft tells me I have no errors when clearly the car has an error. My air suspension being a prime candidate for this. Icarsoft shows "Okay" INPA shows errors 20 & 22 (sensors failing)

Fuse blows on the first shift. Using a BluePoint code reader.

problem still exists, it's been sitting behind the shop, we replace the fuse to start it and move it, but it blows as soon as it's put in gear, forward or reverse, any ideas anyone?

That’s crazy.

Only thing I can think of is your battery and alternator. I would watch voltage live while it’s running. Then see what happens when you shift. I have a feeling that minor pause in engine rpm blows something. Maybe voltage regulator is fried.

Have you tried putting in a bigger fuse? 2 years behind shop, I would have jammed a paper clip in there by now. For science.

I’d start with alternator.

I don’t know shit loads about the issue but being it happens immediately as it goes in to gear I might look at the neutral safety and or the inhibitor switch on the transmission.

Could also be something in the light harness as the rear indicator lights will “blink” momentarily as you pull the shift lever from P to D. (Also making me think neutral safety switch.)

SlickGT1 has a good idea too... not sure how much of a gambler you are but if you physically jump fuse 5, something upstream may “pop up” and give you another direction to follow... bit risky, but if you are to the point of “for science”, he has a good point.