Dead 05 KJ CRD

senatorjohn · **Posted:** Sat May 09, 2015 6:33 am

Killed the Jeep on Wednesday. Accidentally left the scan tool plugged in overnight. Disconnected, and went for a drive. Everything OK. Reconnected the tool to clear the usual codes, air inlet pressure sensor circuit and multiselect transmission solenoid. Drove for less than 5 minutes and the car died. Scan tool would not communicate with the vehicle. MIL would not light up for the bulb check at key on, but would come on after about 20 seconds. No crank, no fuel gauge and a few other lights on. Body module doing all the right things. Swapped engine computers for the one I have previously used to start and run the engine until the security system shuts it down after a few seconds. No crank and run with this computer also.
Looks like I am in for a fun time.
John

gmctd · **Posted:** Sat May 09, 2015 11:44 am

Battery voltage must be above 12.6v or ECM won't start - check for excess oxidation on posts\terminals, which is resistive

senatorjohn · **Posted:** Sat May 09, 2015 10:33 pm

Battery terminals have been on and off dozens of times in the last 6 months, nice and greasy and no corrosion. Battery voltage read over 13V. Currently on charge. Getting familiar with circuit diagrams so I can check all relevant circuits.
John.

senatorjohn · **Posted:** Sun May 10, 2015 6:18 am

Update on battery voltages. 13V when taken off charger. 12.81V key off. 12.66V key on engine off. 12.48V after cranking a few times. Cranking 3.68V - appears multimeter is faulty as engine was cranking over quite strongly. Would have expected minimum of 11V if battery is OK. Will buy a new meter tomorrow.
John

Sir Sam · **Posted:** Sun May 10, 2015 12:42 pm

Try a new battery, these things can still crank nice but the voltage drops too low to drive the Bosch ECU. The Bosch EDC15 ecu seems particularly sensitive to low voltage. Typically 9V is the minimum to drive an ECU, but the bosch does seem to bomb out below 12V.

senatorjohn · **Posted:** Sat May 16, 2015 2:28 am

Problem solved in part. ECM power up fuse no. 14 on the junction block was blown. Next problem is finding out why. Is it excessive current draw by the associated circuits, or intermittent short circuit caused by chafed wire? Only repetitive failures and investigation will find the cause.
John

geordi · **Posted:** Sat May 16, 2015 3:13 am

Fuses aren't perfect devices, they aren't ultra-precise. Also, as voltage drops the current increases, which could account for the killed fuse b/c the computer would still be trying to operate even as the power was dropping too low to be usable.

Change the fuse with the same rating and drive on - worry about it only if the fuse pops again.
If you have a 2006, the wiring bundle that passes behind the fuel filter head usually finds a sharp spot right there to wear through. Look for this and put some padding in there if you see any damage to the coverings.

WWDiesel · **Posted:** Sat May 16, 2015 11:50 am

Just a reminder, as voltage drops, amps (load) can increase exponentially and that can blow a fuse.... :wink:

If it pops another fuse, you can make a couple of wires with male ends to plug into the fuse slot and connect a multimeter to them and read the amp load being drawn across the fuse.... :idea:

senatorjohn · **Posted:** Sun May 17, 2015 4:14 am

Checked the wiring behind the fuel filter when I first got the vehicle. Will check current draw on the circuit to see if it is near the fuse rating. AC clutch is also powered by this fuse, so will check its current draw. Thanks for all the input.
Regards John

geordi · **Posted:** Sun May 17, 2015 11:05 am

Ah yes, I forgot that the clutch is also on that fuse. Since the failure happened while you are driving, it is entirely possible that the clutch is the cause and was drawing just a touch too much power. Dirty contacts in the system also increase the resistance and the load on the fuses.

senatorjohn · **Posted:** Mon May 18, 2015 6:14 am

Died again today on a right hand turn, same as other time. Put in another fuse and started wiggling the harness. no problem when I moved the harness behind the fuel filter or around the computer. Blew the fuse when I moved the harness where it was resting against the auto trans dipstick. Replaced fuse and repeated procedure. Engine faulted but continued to run. No further movement would reproduce the initial result. Removed the over flow coolant bottle and closely examined the harness. No sign of a problem. Next step is to un-wrap harness for closer inspection. Will go for a drive tomorrow to see if I can kill it again. Purchased a better multimeter today so I can do some accurate current draw tests.
John

geordi · **Posted:** Mon May 18, 2015 1:33 pm

There is a fray, obviously - I'd start at the AC compressor and work your way backwards to the transmission computer area and continue from there. A large portion of the harness drops down the driver's side of the engine and runs near the steering column - of course it is under the intake elbow area and hugely crowded - but this is the most likely source of a rub and could pop up when you are turning. This has happened before to others.

Dead 05 KJ CRD

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