Engine died - no crank

Black Bear Jeep (Dan44)

Black Bear Jeep (Dan44)

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Joined
Sep 6, 2024
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40
Location
Athol, Idaho
Today as I was leaving the store, my Jeep (2008 Sahara) died and now has a no-crank problem. When it died, all of the dash lights came on. I got a tow home from my brother, and I am now in the process of trying to get it running again. The battery is new (2024), but I did have a loose connection. Everything is tight now, but it will not crank. During the tow home, with the key on, I put it in gear and let the clutch out. Engine turned over, but the tach didn't move. Engine didn't start.
Things I have done that have had no effect. Replaced the battery in the key fob. I didn't think that was the problem but now I know it isn't. I have swapped 2 relays in the TIPM, same relays, different locations.
Things I will be checking tomorrow: battery cable to the starter, at the starter. Battery cable where it grounds to the chassis/engine. Clutch safety switch. And some fuses. There are several relays with the same part number so I might pick up a relay.
Where else should I look? Ignition switch? This is not as simple as my '48 CJ2A.
This is my daily driver, but not my only vehicle.
I'm spending too much time on Youtube and not finding the right answer.
 
Do you have a multi meter and a test light? If so, do you know how to use them? How about a section of wire with alligator clips on the ends?

Don’t just throw relays at it. You need to do some testing.
 
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Mopar said:
Do you have a multi meter and a test light? If so, do you know how to use them? How about a section of wire with alligator clips on the ends?

Don’t just throw relays at it. You need to do some testing.
Click to expand...

I have several DVMs and know how to use them. I can get a crank when I jumper relay K3. I have less than0.1 volt when I check the MAP sensor. In the process of identifying the fuses to the PCM/ECU. Not labeled very clearly on the TIPM lid.
 
pc1p said:
Have you checked all the fuses? Are you dash lights (CEL, ABS, etc.) coming on when you turn the key on?
Click to expand...

I have lots of lights. PWs work, radio, etc. I'm narrowing it down to the PCM/ECU, an online friend is giving advice (he runs a 4x4 shop). What is common knowledge to him takes a bit to get sent to me.
 
Black Bear Jeep (Dan44) said:
I have several DVMs and know how to use them. I can get a crank when I jumper relay K3. I have less than0.1 volt when I check the MAP sensor. In the process of identifying the fuses to the PCM/ECU. Not labeled very clearly on the TIPM lid.
Click to expand...

Just something to keep in mind - the MAP sensor (among other things, including your fuel pump, injectors, etc.) will only show voltage for a brief period during the initial "key on". The ECM will energize the ASD relay for ~2-3 seconds, after which time if there is a no-start situation (with no crank), it will disable both the fuel pump relay and ASD relay.
 
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IT was hard to look for the cause. An internet friend pointed out where to look. But the lid to the TIPM has the fuse labels, but too small for me to read easily (old eyes). I asked an A.I. to give me a list of all of the PCM/ECU fuses and sensors. I do not trust all A.I.s, not even the one I asked, but in this case it gave me a list of fuses. Turns out it was the second fuse in the list. It wasn't the battery, or the cables, or the ignition switch. Just one bad 10A fuse. I have extra fuses on hand now.
 
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Black Bear Jeep (Dan44) said:
IT was hard to look for the cause. An internet friend pointed out where to look. But the lid to the TIPM has the fuse labels, but too small for me to read easily (old eyes). I asked an A.I. to give me a list of all of the PCM/ECU fuses and sensors. I do not trust all A.I.s, not even the one I asked, but in this case it gave me a list of fuses. Turns out it was the second fuse in the list. It wasn't the battery, or the cables, or the ignition switch. Just one bad 10A fuse. I have extra fuses on hand now.
Click to expand...

Likely also a worthwhile effort to trace the harness to see if there is rub through somewhere - it’s rare that a 10A fuse pops for no reason (internal corrosion is known though no common).
 
Black Bear Jeep (Dan44) said:
I found fuse M28 blown. I replaced it and she runs! Yay!
Click to expand...

Literally what happened to me. I ended up blowing a couple grand in parts before narrowing that down. Because I am stupid. I ended up putting a 20a fuse in there because when I initially replaced it, it blew again while I was driving.

I had ended up completely replacing all my wires with the Jeep Cables set, had my TIPM tested, bought a bunch of new relays, etc. I even replaced my starter and alternator. Nope, it was a single fuse.
 
Important rule of diagnosing…always start with the cheap or free stuff first.

Yes I have also ignored that rule and replaced good and expensive parts…….
 
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Mopar said:
Important rule of diagnosing…always start with the cheap or free stuff first.

Yes I have also ignored that rule and replaced good and expensive parts…….
Click to expand...

The Jeep Cables were a good investment at least. I noticed a huge difference in how my Jeep started after I replaced the stock battery cables and ground wires.
 
I've still been experiencing blown fuses. It only does it when the engine is warm and the outside air temp is warm (~90). I've replaced the fuse 3 times since my first post. I used a 15A to get home, and replaced it with a 10A once I got home. I've checked the plugs on the bottom of the TIPM and at the ECU. At the ECU, there are about 7-8 inches of wires exposed (no wire loom), and the wires were lying against a plastic cover. I could find no bare metal in any of the wires. In the cool mornings, I have no problems, but once the day warms up, I will need a fuse.
The connectors at both ends are clean, but everything under the hood has a fine covering of silt or thin mud. I guessed the previous owner had fun splashing through some puddles.
I carry extra fuses now.
 
The problems are growing. The fuse thing I found and replaced. I thought I fixed it, but today doing a short trip, under 10 miles, I picked up 2 new codes. My current codes -> P0403 (EGR circuit), P0344 (camshaft position sensor), C121C (torque request signal denied). I "think" it is in the wiring harness from the TIPM as this has been the only thing I have been working with at the ECU end. Wires don't bother me, but I'm at a point I'm thinking to replace it all.
 
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