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Possible Bad Crank Position Sensor Or Other Electrical Issue? (Won't Crank)

2K views 33 replies 10 participants last post by  rep-tile 
#1 ·
Hi, I have a 2002 Overland with the 4.7 H.O. and I'm having some weird electrical issues and the Jeep won't crank.

With a new battery, the dash is only showing around 9-10 volts and is possibly a bit dim. When turning the key forward, the Jeep won't start and the starter doesn't turn over or make any noise. The headlights seem about normal brightness, though the dash seems a bit dim.

I've checked every relay under the hood and tested all the fuses, as well as inspected all connections and wiring, including ground points and battery terminals and everything seems okay as far as I can tell.

I'm not getting any codes on the dash when doing the key dance.

Does this seem like a Crank Position Sensor going bad? A friend of mine seems to think it might be the starter, but a new Mopar starter was put in this Jeep not too far back and this starter probably has less than 70 or so cranks on it.

Thanks for any help. :)
 
#2 ·
I'd check your battery voltage directly on the battery, not using the Jeep sensors. Sounds like it's low. My first thing would be to charge it on a charger to it's full 13 or so volts. See if it holds a charge. It's possible that your new battery is bad. Low voltage would cause the symptoms you're describing. If it holds a charge, then the alternator could be bad and not charging the battery while driving. I think this would cause a check engine light or battery light though. Can you stick another battery in it that you know works and kicks out 13 volts? That will help rule out these two theories. If those two are not the cause, then you could have a loose wire somewhere between the battery and the starter.
 
#3 ·
With a meter check the battery directly from terminal to terminal , not on the cable but the post itself, a fully charged battery should be about 12.6v or maybe a bit more. Start the vehicle put the meter back on the terminals you should now see about 14.6 or so with the vehicle running.

Less the 12.6 with the engine off and the battery is weak. Less than 14.6 +or - with the engine running and the alternator is not charging properly.

With the engine off check the cables themselves with the meter. Cable to cable do you still get the same 12.6 that you get from battery post to battery post?
If not the cable where it attaches to the battery post has a bad contact.
Check from the negative terminal and put the red wire down on the starter bolt where the big red battery cable attaches. You should see 12.6 there also. If you don't you have a bad connection or a bad cable.

No I don't think a bad crank sensor has anything to do with this particular case.
 
#4 ·
Sorry, I forgot to mention earlier that we've tested the battery and it tests okay on the meter. It's actually brand new. It showed 12.75 volts on the meter. I was in a bit of a hurry this morning so I neglected to mention that. The Jeep has produced the same results with 2 batteries, both of which tested okay, so I'm pretty certain both batteries are good to go.

The Jeep won't actually start, so I'm not able to test the voltage with the engine running but my next step is to test the starter as soon as I can get back to it with enough daylight left. :)

Thanks for the responses so far.
 
#5 ·
No crank condition has nothing to do with the crank sensor. Chances are you have badly corroded battery cables, which WJs are prone to. You need to splice the cables insulation near the battery connectors to see the actual conditions.

Here is a pic of my cables that "seemed" totally fine.
 

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#6 ·
12.75 is perfect. You now just néed to check the cables to the starter and the main ground point. By placing you meter on the ground at the battery and the little red meter wire to the starter bolt where the red battery wire connects. 12.75 is what you should see. Repeat the procedure to the bolt where the big black battery ground wire attaches to the engine or firewall. 12.75 is what you're looking for there also.
 
#8 ·
^ Neutral safety switch is also a possibility. The starter will not engage without an input from it. It's easy to bypass. All you have to do is disconnect the black round 3-wire connector located on your transmission. Connect the middle pin of the connector to a good ground (such as the transmission outer case) with a piece of wire. First you can try throwing the gear lever in neutral to see if that helps.
 
#10 ·
Thanks for the responses for far, everyone. Between the rain we've been having here and me getting home so late lately, I haven't had time to do much to it yet. I hope to get back to work on this issue this weekend.

I did try cranking with the Jeep in neutral with no luck. I don't notice any corrosion on the battery terminal cables but maybe I need to cut back the insulation and check them. rep-tile, were you able to see the corrosion by just pulling back the insulation or did you just sort of jump in and start cutting? I know I need to have a deeper look, but I hate to chop my cables all to hell if I can avoid it lol. >:)

Thejarhead, I plan to check the cables and everything as you've mentioned, as soon as I can get home in enough time with some daylight left. :D

Thanks again everyone. I'll update this as soon as I am able to do some more testing.
 
#13 ·
I don't notice any corrosion on the battery terminal cables but maybe I need to cut back the insulation and check them. rep-tile, were you able to see the corrosion by just pulling back the insulation or did you just sort of jump in and start cutting?
I had to strip a portion of insulation down to the bare wire with a cardboard cutter to expose the corrosion. There was absolutely no way to tell except maybe that the insulation appeared slightly discolored. Needless to say I wasn't expecting this. You can always cover it with some electrical tape if it turns out fine.
 
#11 ·
Check for voltage drop across the battery cables. I'm sure there are plenty of YouTube videos on checking voltage drop. Do you really have battery voltage at the big terminal on the starter? After checking voltage drop on both the POS and NEG cables, don't rule out the starter just because it's "new".

As @rep-tile said, the crank sensor has nothing to do with the starter. It's a sensor that gives input to the computer as to the position of the crankshaft.

I started the search on YouTube. https://www.youtube.com/results?search_query=no+crank+no+start

Here's a search in YouTube on voltage drop. (might be covered in the "crank no start") https://www.youtube.com/results?search_query=voltage+drop
 
#12 ·
Another supporter of the batt cables being the issue. I swapped out my entire harness due to it being so bad. It connects the batt temp sensor, alt connection, an engine block connection, and probably a couple more. A little tedious but not a big operation.
 
#14 ·
Small update to this, I did as much probing as I could this weekend, before it started to rain... again... :brickwall

I tested the cables and ground at the starter and I'm getting almost exactly the same voltage as at the battery (Almost 12 volts).

I tried again to start with the Jeep in neutral and wiggled the shifter as I started, with no change. I also notice the reverse lights come on when I shift into reverse, which I've read means the switch is likely okay?

The dash is still dim, but both headlights and taillights seem normal. There is no clicking or any noise whatsoever from the starter or the dash, etc.

I didn't make it as far as bypassing the switch before it started to rain on me. I'll try to get to that asap.

I did try to bypass the solenoid switch on the starter, just for the hell of it and it did make quite the spark, but no start. :D:rofl:

I did hold off on cutting open the battery cables apart, since I seem to be getting good voltage at the starter. Wouldn't that mean the problem is likely somewhere else? If not, I'll pull back the insulation and check those out.

I'll swap out the harness if necessary, as much of a pain as this has been, it'd be worth it just to be done with it. (Of course, I'll check everything else that I can first.)

Thanks again for the help everyone, I really appreciate the input.
 
#17 ·
I tested the cables and ground at the starter and I'm getting almost exactly the same voltage as at the battery (Almost 12 volts).
Voltage doesn't mean much. It doesn't just take voltage, it takes amps to run the starter, lots of it. A resistance test would have told you a lot more than a voltage test. If you have corrosion in your cables, it will create resistance, which means a significant amp drop.

I tried again to start with the Jeep in neutral and wiggled the shifter as I started, with no change. I also notice the reverse lights come on when I shift into reverse, which I've read means the switch is likely okay?
No because the reverse lights are triggered by a different prong on the NSS.

Oh, one other question out of curiosity; would the neutral safety switch be responsible for the voltage drop that my dash is showing? The reading of 9 or so volts? Perhaps the thinking here is that the switch possibly being bad may be causing the voltage drain/resistance?
No the NSS doesn't consume power, it is just a switch which input allows the starter to engage. The voltage drop is probably the load from the starter. If there isn't enough amp to run it, though, it is not going to turn over.

Have you done a load test? Batteries can have a charge of 12.6v but if, under load, it drops to 9, then you won't get a crank. Do a load test before standing by that battery.
Battery is a possibility. Note that bad battery cables will also cause a battery not to charge properly and shortens its lifespan.
 
#15 ·
Oh, one other question out of curiosity; would the neutral safety switch be responsible for the voltage drop that my dash is showing? The reading of 9 or so volts? Perhaps the thinking here is that the switch possibly being bad may be causing the voltage drain/resistance?
 
#18 ·
I haven't done a load test, because I was pretty certain the battery is good. I bought a brand new one for this when the Jeep first began exhibiting this problem, thinking it was likely the battery at fault. The old battery was showing the same voltage on the Multimeter and on the dash and the new one has displayed pretty much the same readings, on meter and dash.

The only time I've ever had cranking issues with this Jeep in the past was because of a dead battery (a few years ago) so I'd figured this was the same issue again and bought a new battery. When the old battery seemed to show good voltage, I'd assumed maybe it was a dead cell or something, since the battery was a few years old at that point.

Just to clarify, my dash is showing only 9 Volts just by simply turning the key forward, even without trying to start it. I can turn the key to the On position and it shows 9 Volts, but turning it all the way forward to the Start position shows no change. I still get 9.

I will check the NSS as soon as it dies out enough for me to climb back under there. :D
 
#19 ·
I second the load test on the battery. You may have 12 v all day long but low amperage will not "push" that voltage to turn the engine.
If that comes back good, you've got little other option other than to freshen the cabling connections to the starter.
Then...if still no joy, short of finding a new harness, can you configure a supplementary wire (heavy) to the starter to be certain you have a good connection? (Be mindful of + & -)
The other route is to remove the current harness create new cabling & terminal ends and reinstall.


It's not as daunting a task as it sounds.
 
#20 ·
Read the battery voltage while jumping those two wires on the starter together.

You making a lot of sparks and no starter spinning has me wondering..............

If voltage stays above say 9.5v and engine won't turn over when you jump those wires together try rotating the engine by hand. If you have a battery charger I'd consider charging it some.
 
#21 ·
Read the battery voltage while jumping those two wires on the starter together.

You making a lot of sparks and no starter spinning has me wondering..............

If voltage stays above say 9.5v and engine won't turn over when you jump those wires together try rotating the engine by hand. If you have a battery charger I'd consider charging it some.
Interesting thought...86cj has.
When did it last run correctly? What else was happening at that time? Hot day, short trip, long trip, any overheating, any codes, etc.?
 
#22 ·
You can always remove the starter and use jumper cables and make sure it free runs on the bench

Edit. If you pull the start relay from the junction box beside battery and jam a wire in the 87 slot and touch the plus post of the battery and the starter starts turning over the engine you have a problem with the ignition switch or TRS plate.

If the starter makes a loud klick and you read battery voltage on the big wire of the starter the reman starter may be bad or is bad.

If you hear the klick and voltage drops to say 9-10v try and rotate the engine with a socket and breaker bar on the crank bolt. If you can't turn it over pull the belt off and try rotating it again.

If you can now rotate it with belt off spin accessories and see which one is seized.

If you can't rotate it with belt off.............

A free running test of the starter is still a good test.
 

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#23 ·
The Jeep last ran correctly around the first of this year I'd guess. Maybe January or so. There were no problems of any sort that I'm aware of and no codes that I recall. It sat for about 2 months in the cold without being driven but prior to that it always ran fine. When I returned to it after those 2 months, it wouldn't crank. I'd assumed the cold had killed the battery, so I replaced it with a new battery (recently). I'd been a bit busy, so I hadn't had much time to mess with it.

Of course the new battery didn't fix the issue and both the new battery and the old one were showing good Voltage on the meter, but only 9 or so on the dash. Both then and now. I'd only replaced the battery just in case.

The Jeep went from running fine for years, to not starting, just from sitting in the cold for a few months. :|

The last time I'd driven it before sitting, there was nothing abnormal about it that I'd noticed. I'd probably taken 2, 45 minute trips or so, at different times of the day with no overheating, or stalling or anything. Just normal operation. It sat up soon after that.

I'll try to jump the starter with some secondary wires and I'll also check the Voltage while jumping the wires. I'll also try to turn the engine by hand and do a load test on the battery. Before I started back at this, I'd put my battery charger on the battery to make sure it was fully charged and the charger says full charge as of a few days ago. The battery has been disconnected each time since then, so it doesn't discharge. I'll put it on the charger once more, just in case though.

86cj74.2L: It's funny you mention trying to start the Jeep from the relay box like that. When I was researching, I came across a video where a guy did something very similar to what you mention and thought I'd give that a try. I think I'll try that when I get home tonight.

Thanks again everyone.
 
#25 ·
Update: I tried starting the Jeep from the relay box and it worked! The Jeep started right up and ran like everything was normal. The dash was still showing 9 Volts when I turned the key forward but the Jeep started without hesitation.

Once the engine was running and the alternator was charging, the Voltage on the dash showed normal levels.

I guess this means the Neutral Safety Switch is bad after all? :smile2:
 
#26 ·
Disconnect the NSS connector and run an alligator clip jumper wire from the middle prong of the connector to the frame (you can use the transmission casing or anything else as long as it's bare metal) this will bypass the switch. Just make sure you're in park while you run the test.
 
#29 ·
Ahhh so it looks like the Transmission Range Sensor is likely bad then, given that it's a 545RFE and 4.7? That looks like it's gonna be a fun job. :mad::rolleyes:

One of the first things I tried was swapping the starter relay with another to test if the relay was bad. Actually, I tried several surrounding relays, just in case. No dice. :frown2:
 
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