View Full Version : Tracking a Short Help Requested

October 6th, 2017, 22:05
01 XJ 4.0 Automatic 165k miles.
Anyone have any knowledge of shorts in the starting sequence. 2 days ago drove home from work with no issues. Pulled in driveway shut it down and waited on the wife to come out to run to grocery store. When she came out I attempted to start it. No response at all. Tried one more time and nothing. Thought maybe one of the terminals was loose but all were solid and no corrosion. Let it sit a few minutes and it started right up. Drove it to and from work since then with no problems until I stopped to get gas on way home tonight. Filled the tank and went to turn on and same thing. No response, but lights turn on, radio turns on but the head unit had completely reset like the battery was dead (did this both times). I waited 10 minutes tried to start again amd nothing this time. Had the wife come get me and just in case tried to jump it off with no success.
Any ideas or input would be greatly appreciated.

October 7th, 2017, 04:01
Check connections at starter.

October 7th, 2017, 06:17
You don't have a short.

Begin by cleaning the battery cables and terminals completely.

October 7th, 2017, 07:21
Loose ground

October 7th, 2017, 08:39
Possibly. OP needs to start at the battery and work back from there.

October 7th, 2017, 21:12
Loaded tools up and tried everything mentioned and then some. All grounds were good. Terminals and cables cleaned and tightened. Tried it in neutral and nothing. Off to the shop out goes.

October 7th, 2017, 21:22
Nuetral safety switch can be bad and won't let it start in park or nuetral I've gone through probably 3 in the last 5 years in my 94

Rob Mayercik
October 9th, 2017, 10:29
Nuetral safety switch can be bad and won't let it start in park or nuetral I've gone through probably 3 in the last 5 years in my 94

Interesting thought, but that wouldn't deprive the radio of power.

October 12th, 2017, 17:28
For what it's worth (and future reference), there's two kinds of shorts- a short to ground and a short to power.

For most folks, a "short" is short for a short to ground. That is to say a wire with voltage flowing across it somehow connacted a body panel, a ground wire, the enhine, a metal part attached to the engine, etc. The most common symptom of a short to ground is a blown fuse. That's what they're there for. When the wire shorts to ground, it wants to pull as much amperage as it can (which is as much as the battery will provide.) Ever accidentally welded a wrench to battery terminals or when you were trying to remove a starter? You get the idea. To trace a short to ground, I like to break the circuit into as many "pieces" as possible by disconnecting connectors. Then I break out my DVOM, set it to read resistance, and starting poking around. Place one lead on the wire or "piece" of the circuit you want to test and the other on a good ground point. Pretty much any old sheetmetal bolt should work. An "OL" reading indicates "these are not the droids you are looking for", but low resistance indicates you have found the "piece" of the circuit that is shorted. A good, visual inspection of said piece should reveal the short.

A short-to-voltage is a little bit different. This is when a circuit that have a set amount of voltage or variable voltage becomes shorted to a circuit with more or non-variable voltage. A great example would be the signal wire gor a TPS shorting out to the 5-volt reference wire. Indeed, sensor circuits are the most suspectible to shorts to voltage, and as a result, the most common sign of one is a CEL with an associated DTC. However, the same basic rules apply- break the shorted circuit into "pieces", break out your DVOM, but test for voltage on the circuit instead of continuity.

October 15th, 2017, 08:45
Wiggle the PRNDL and see if it starts in neutral. Thats the neutral safety switch. The next thing to do is jump the starter at the starter. The round end of an adjustable wrench works well. A remote starter switch also works better.

This will prove the starter is good and not failing due to heat.
Next swap relays in the power center with the AC relay to verify it has not failed.
Sadly the next may be a corrosion problem. If the backup lights work in reverse with ignition (good ground)on I would check the neutral safety switch connector which is by the trans dipstick unplug it and check for corrosion. This is a good place to start.