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Optimized Idle fails, check engine light.

When I have optimized idle set on the truck, I hear the warning buzzer that it's about to start up, it gives about half a crank, and then goes dead without starting and gives a check engine light. When it does this, it will not start until I reset by turning the key off about 10 seconds and then restarting, clearing the code in the process. It's not all the time, and usually happens in the middle of a long cycle like during a 10 hour break. There have also been a few times where the buzzer sounds and the engine doesn't even attempt to crank. It goes directly to the CEL. It also doesn't always happen, but usually a few times a week, and doesn't leave any lasting codes.

I've had it in the shop and they said everything was working normally and don't pick up anything in the code history.

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I was able to get back into a dealer and actually talk to the forman there. He said there was a service bulletin out for my DD15 (didn't say if it only affected a certain year model or range) about this issue. It had to do with a wire harness replacement or adapter. He wasn't too clear on all the specifics, but basically what was happening was the ECM would get a false reading that the truck was trying to move during the automatic startup. I.E. as if it was in gear. He said the threshold is very low and even a 1 mph detection would trip the safety. Even though the truck was out of gear and didn't move, the ECM would occationally think it is. Symptoms are the half crank startup like I originally mentioned, only happens periodically and can't reproduce on demand, the check engine code SPN001663, and no lasting codes once it's cleared up.

It will take a while with this cooler air to know if this repair fixed the issue for good, but have had a few cycles since then and all started ok.

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6 Answers

do you have really good batteries. I have 2000 S60 with optimized idle. my truck need LOTS of amps to start the truck and keep computer going that runs optimized idle. I have 4 1,000 amp batteries and it always starts. I use to drive a company truck that also had optimized idle and it alway had trouble. once the starter kicked in all the power when to starting the truck. Than the optimized idle would turn off.

My truck has light in dash that comes on you turn on optimized idle. If the light bulb burn out I can't even raise idle for sleeping or anything. Not sure how the new system is but in my older truck it really tied into the truck. Detroit told me their was nothing worn because their was no codes in computer. Well their is no code for light bulb burned out in older optimized idle system, Their is no code for not having enough batter power and it not the 12v it the amps you need, well thats what my truck needed

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The truck is a 2012 model with 33000 miles on it total. The batteries haven't been tested, but I've had it draw down to the low voltage cut off and still start as if they were fully charged. So I know that's not the problem when trying to start based on the temperature settings.

It happened again last night and I was able to pull the fault code from it. On the diagnostic display, it read:

"Engine 000 SPN001663

Idle Mgmt Itlk 07"

I was able to find a fault code list from another question on here and under the SPN column of codes, I found one listed as 1663, and the description said "Optimized Idle Safety Loop Faulted." Could this be something as simple as one of the safety switches (clutch, shift lever, or hood) being overly sensitive/defective, or something deeper like faulty electronics? Being a company truck, I don't want to start digging into things myself. I'm looking for what direction I need to point the shop in.

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I have been idle my truck all nigh because of heat. I also had a engine aux output drive 8 electrical fault on dash display. So i was going to use optimized idle tonight. Not working. Dash light for optimized would not turn on. So i check the bulb. It was burned out. I put new one in and my dash warning for engine aux output driver 8 also went away.So their is a code if the bulb goes out on the dash on my old 2000 truck.

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If it's not the light bulb, have the optimized idle controller box, ECU and cab thermostat checked for correct programming. Also check to make sure you have good, strong batteries and that your wiring is in good condition. It could also be a defective hood, shift lever or clutch switch.

Have the shop do a through inspection of all of the components in the Optimized Idle system, and they should be able to find the issue.

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you may check the hood safety switch, on mine it's mecury switch, you should be able to test by putting a jumper in the plug.

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I have that system on my 07 Century. It stopped working in 09. No one can seem to fix it.

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my 02 didn't work when i bought it, took some time to figure out why. turned out i would of had to have the 5 min auto shutdown enabled.

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I am maintenance director at MAG Carriers/MAG Transportation. We have all 2015, 16, 17, and 18 Freightliner Cascadias. I have had this problem with a few of the dd15's. Check for loose ground wires on the starter. I had one that the nut holding the wires on the ground stud of the starter was missing/gone all together. It's a common problem with them elsewhere as well. This also could cause charging issues which could be another cause for not only the optimized idle to fail but startup all together.

Only other cause I've seen for this fault is yet another very common issue for quite a few other electrical faults with the new Cascadias and that's the main power disconnect. It can be unplugged and not active in the system at all but make sure it is in the "ON" position before disconnecting the switch from directly through the floor. It is a small 3 wire plug and very easily accessible for disconnecting.

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