CRD Died While Driving

tigafila · **Posted:** Sat Aug 16, 2014 12:03 pm

Hello group, my CRD (183k) died while driving Thursday night. It was like someone turned the key off and as it happened I first noticed the tach and speedo instantly went to zero and I looked up at the EVIC and the outside temp read -40F. I popped it in neutral while I was coasting, hit the key and nothing. When it stopped I tried the key again to see if it was clicking or cranking or some sign of life and there was nothing. I visually checked the fuses on the side of the road and towed it in. I had a few minutes last night and only had access to my scan tool, no volt meter or even a test light, there is no communication with the scan tool whatsoever. I am going out now to start checking fuses, power, etc., but would appreciate any input. I did several searches and didn't find any posts with these particular symptoms, maybe I'm breaking new ground again. :banghead:

Thanks in advance, Tigafila

WWDiesel · **Posted:** Sat Aug 16, 2014 1:22 pm

Get yourself a voltmeter if you do not already have one and a 12 volt test light. Start at the battery checking for power 12 volts. Check main fuse in under hood fuse box. Sounds like you have either lost the battery or a major bus failure?
Batteries do completely die sometimes, internal failure, seen it a couple of times.
Good luck, let us know what you find! :wink:

geordi · **Posted:** Sat Aug 16, 2014 1:44 pm

Sounds like the battery either completely failed - seen that before plenty of times... OR the alternator quit and sucked the battery dry and it finally quit when it didn't have enough power to run the computer.

Diesels don't require a lot of power to run, so it could have been a LOOOOOOONG time between losing the alternator and losing the battery entirely.

Try a known-good battery first, and proceed from there.

tigafila · **Posted:** Sat Aug 16, 2014 2:53 pm

Update, fuse 14 in dash blown, replaced and drove, runs fine but I still don't know what caused it to blow. Any ideas?

geordi · **Posted:** Sat Aug 16, 2014 3:56 pm

What is fuse 14 powering? I don't have the chart memorized...

papaindigo · **Posted:** Sat Aug 16, 2014 4:17 pm

05 and 06 - interior fuse 14 is PDC Fuel Pump/AC Clutch, Starter Relay/Engine Controller/Transmission Controller (Diesel Only)

geordi · **Posted:** Sat Aug 16, 2014 5:37 pm

Ok - reasons why your engine died and was instantly cold-dead: That fuse powers both the ECM and the TCM. No computer, no workee.

Now, reasons that I can see why that fuse would have popped... The starter is a relay, so that shouldn't be feeling full power, and it happened while you were driving. So eliminate that. The AC however... It SHOULD be a fairly light load to activate the electromagnetic clutch, but perhaps with the summer heat, the resistance in the wires rose *just enough* to kick the fuse. If that one burns again, step up one size in fuse and see if it fails again. A dead short in the electromagnet clutch will burn the fuse before ever imperiling the wiring, so no fears of overheating any of the wiring. Most vehicle wiring is oversized for the job anyway, so that the fuses can be the weakest link. Even with that, there is still a significant safety factor involved.

tigafila · **Posted:** Sat Aug 16, 2014 7:18 pm

I hate intermittent shorts! :dizzy:

naturist · **Posted:** Sat Aug 16, 2014 9:56 pm

tigafila wrote:

I hate intermittent shorts! :dizzy:

There is no doubt intermittent problems blow chunks. Hope you find it quickly.

Billwill · **Posted:** Sun Aug 17, 2014 4:56 am

tigafila wrote:

I hate intermittent shorts! :dizzy:

Yeah that is the worst type of problem to have!

First thing is have a full range of spare fuses with you at all times and then try to follow the various harnesses wherever you can access them to see if there is any chaffing through to the chassis somewhere.

If you do not already have the circuit diagrams available then download your 2005 KJ Service Manual here...includes the circuit diagrams http://www.colorado4wheel.com/manuals/Jeep/KJ....and get a reasonable Digital Multi-meter to try to track down where the short may be coming from.

You can also put the Meter into DC AMPS 10 Amps Mode or higher and put it in series with any fuse that keeps blowing..you may find that circuit is drawing very near to its rated fuse value and just by switching on some extra item such as the air-con you go above the level that the fuse can handle. You then need to track down what is causing the initial high amperage being drawn. :wink:

WWDiesel · **Posted:** Sun Aug 17, 2014 11:35 am

My bet would be on the AC clutch. If it happens again and conditions allow, unplug the AC clutch power wire and drive around for a period and see if it happens again. If it does not, you have found the problem! If it pops the fuse with the AC clutch unplugged, problem is elsewhere.... :roll:

You could just turn the AC off on the dash, just remember the AC runs in several different settings even with the AC button turned off unless you have done the switch mode like some of us have?

geordi · **Posted:** Sun Aug 17, 2014 1:19 pm

You really are a sadist, you know that?
Drive around in August with the AC off? That is just cruel and unusual punishment.

If the fuse was 15 amp, bump it up to a 20. If it was 20, bump to a 25. The individual wires are more than capable of handling that small increase in power, and if the AC is the source of the short, the fuse will still pop the same way. Dead shorts jump the amperage to maximum almost instantly, and the total length of each wire segment is part of what determines how much power it can take.

The fuse is (by design) narrower than the cross-section of most of the power wires in the car, even at 5amps over the current rating. Obviously, the system is *right* at the threshold if it isn't popping instantly when you start the engine or the AC, it has to build up resistance in the wire. The heat of summer is what is helping that.

If the fuse does pop instantly, or in any predictable way (like only when the AC cycles on) then that is the answer - something is shorted.
Intermittent problems are a huge pain however.

Do you have an 06? The wire loom behind the fuel filter is a popular place to rub through, causing no end of haywire operations. Check there for damage.

dkenny · **Posted:** Sun Aug 17, 2014 7:13 pm

rig a light bulb in place of the fuse..if its a short the light will light and not burn up the wiring.
use a 55w halogen light bulb. you might need 2 or 3 in parallel if the circuit actually draws
that much current.
I would suggest against upping the fuse size..why? so the intermittent shorts draw 22 amps on the 20amp fuse
yes this will pop a 20amp fuse but not a 25amp..so where is the extra heat going..the worst place..melting the
insulation on the wire..making to thinner..leading to more hard to find shorts..or fires..

-dkenny

WWDiesel · **Posted:** Sun Aug 17, 2014 9:02 pm

geordi wrote:

You really are a sadist, you know that?
Drive around in August with the AC off? That is just cruel and unusual punishment.

Heck, he's in Ohio, he does not have to deal with the GA heat and humidity like we do.
Ride around for a while with the windows down, no sweat!!!! :lol:

I agree with the next size fuse test, only problem is, that may be masking the root cause.
My money is still on the AC clutch! :SOMBRERO:

user113 · **Posted:** Sun Aug 17, 2014 9:54 pm

dkenny wrote:

I would suggest against upping the fuse size..why? so the intermittent shorts draw 22 amps on the 20amp fuse
yes this will pop a 20amp fuse but not a 25amp..so where is the extra heat going..the worst place..melting the
insulation on the wire..making to thinner..leading to more hard to find shorts..or fires..

-dkenny

Fuses are not some sacrosanct holy interrupters that trip instantaneously. In fact, they will probably run indefinitely at 110% of current rating. At 135% of current, they might last close to a second or as long as 10 seconds. At 200% of current rating, less than a quarter second to perhaps 5 seconds.

So if the "short" (i.e., --the problem--) draws 22 amps (i.e., 110% of rated current), a 20 amp fuse will not trip for a really long time, possibly not at all; probably longer than you would want to wait.

Now, if it really is a "short" where the +12v is connected to ground, there will always be the battery's internal resistance in series with the circuit. The internal resistance for car batteries is measured in milliohms, often in the low single digits. Even assuming a ridiculously high internal resistance of 0.1 ohms to model a possible maximum current (i.e., 100 milliohms), the current in the short would instantaneously draw over 100 amps (138 amps for a fully charged battery). That would be at least 400% of current rating of a 25 amp fuse, which would not be tolerated more than a half a second. So for a true "short" to ground, there really isn't much difference between a 20 amp and a 25 amp fuse!

See http://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/blade-fuses/littelfuse_mini_58v_datasheet.pdf.

Of course, this shows that fuses are relatively poor tools to measure current. A better way to measure the current in a circuit would be to use an ammeter as suggested by Billwill, but an even much better idea would be to put a really low resistance, high power (say 0.001 ohm) shunt resistor in series and use your voltmeter to measure the voltage drop and calculate the actual current, like the cheap car starter current meters do, or use a clamp on meter like the pros have.

See http://www.rcgroups.com/forums/showthread.php?t=393591.

boilermaker2 · **Posted:** Mon Aug 18, 2014 9:42 am

I would not get a one step higher fuse when my ECM/TCM was involved. Those two items have enough problems. I would check the A/C. Remember that full floor, floor/drefrost and defrost setting all trip on your compressor whether you have the A/C button pressed or not.
Boiler2

WWDiesel · **Posted:** Mon Aug 18, 2014 5:57 pm

boilermaker2 wrote:

I would not get a one step higher fuse when my ECM/TCM was involved. Those two items have enough problems. I would check the A/C. Remember that full floor, floor/drefrost and defrost setting all trip on your compressor whether you have the A/C button pressed or not.
Boiler2

That is the reason I suggested unplugging the power wire to AC clutch for a test. Makes no difference what position the selector switch is placed in.... Unplugging the AC clutch is a simple test to rule it out :wink:

I also agree with not going to a higher amperage fuse; as I posted earlier, it would only mask the problem and getting to the root cause is most important especially since you are dealing with a circuit that also supplies both on board computers.... :2cents:

Billwill · **Posted:** Tue Aug 19, 2014 4:58 am

Which fuse 14 blew? The 10 Amp fuse inside the cabin or the 40 Amp fuse under the hood? That 10 Amp fuse 14 does indeed power the ECM and TCM which is why the Jeep died completely.

The following advice is based on it being fuse 14 (10 A) inside the cabin that blew....if it was the other fuse 40 Amp under the hood I will post later!

A Pink/White wire comes out of the interior fuse box (Junction Block) and goes to ECM,TCM and Mass Airflow Sensor.

So the air-con has nothing to do with it.
You need to physically trace this Pink/White wire to all the places it goes to look for any fraying to chassis

When I was in Support in the Field fixing Mainframe computers etc. I used to carry a selection of DC circuit breakers in the most common current range used. I could then replace the fuse with the circuit breaker while trying to find the problem! :wink:

CRD Died While Driving

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