Intermittent Starting Issue 07.5 2500 6.0 LT

danmdevries · December 29, 2016

Twice towed into local dealer unable to replicate the issue. Yet it persists.

First time was a warm restart. Drove about 4 miles in traffic so most everything up to temp, ambient 20°F. Stopped at store, came out and turned the key. Engine fired, fast idle'd to 1500, but on the "settle" it didn't stop and the truck turned off. Started again and it stayed running. Drove another 4-5 miles in lighter traffic 40mph ish, and got to where I was going. Got back to hot truck after 5 minutes and turned the key. It acted as if the battery was totally dead. No lights, nothing. Turned key back and out, retried and it started for a second or two, but shut off. Repeat, tried giving it throttle but no response and it shut off. Third time nothing happened again. Sat for a few minutes, and tried again it started fine. On the drive home had two very brief instances of the truck shutting off. Less than a second each. Dash turned off (no warning lights or anything, gauges just went to zero) and no throttle response but it came back immediately. Got home and it wouldn't restart. No crank. Had it towed in. After two days they said it was the battery. I wasn't on board with this diagnosis, but they said there were no codes and couldn't replicate the issue so whatever, throw a battery in. I'd put the existing battery in the truck a year prior, though it came out of my old truck and was replaced a year before that. So a two year old Interstate battery.

Drove it around back and forth to work for a week without issue.

Second time was exactly the same drive loop as when the problem first showed up. Drove to store, 4miles in traffic, ambient temps around 20, then another 5mi to work for a brief stop. Came out and turned the key, engine fired and high idled, but instead of settling down, just slowed to a stop. Did this a couple times, no CEL, nothing abnormal on the dash. After a dozen or so tries, it stopped engaging the starter and acted like a 100% dead battery. Grabbed multimeter, had 12v at the starter. Had it towed back.

A week or so in a loaner car, and they can't find anything wrong. Starts every time. Cold/warm/hot, no issues. Drove it a total of 30 miles, logged a hundred starts. No codes, unable to replicate the issue.

Last night I drove to work without issue, but as I was walking out I hit the remote start. Heard it start, but it died on the idle down. Didn't reattempt remote start as I figured I was going to be calling a tow truck again. Got in the truck, turned the key and it fired immediately but died on the idle down, would not take throttle. Third time it was normal. Drove home without issue.

Any suggestions? I'm a former (non-car) mechanic and typically do my own work, but this is the newest vehicle I've ever owned and the interconnected electronics are not my thing. From what I've read, it looks like I need to chase after the theft protection system, but the only references I could find were on older half tons. My google searching didn't turn up any matches in the HD family, and the majority were older model years.

Cold idle and low throttle input when cold have variable RPM. Not terribly so, but noticeable. I would think IACV, but not sure these trucks have it. Has been this way since I bought it last year.

The things I've found for this problem are almost exclusively posted regarding the half ton, and lead me to think it's theft control module failing.

Any other takes on the issue?

Raptordude · December 29, 2016

Sounds similar to what my truck did. Try a new crank position sensor

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danmdevries · December 30, 2016

Sounds similar to what my truck did. Try a new crank position sensor

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Shouldn't that trigger a code?

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Raptordude · December 30, 2016

It didn't when mine went bad, but in some cases it might. Man that was a pain. No lights, no codes, would only do it sometimes. It would either run 100% fine or not at all. There was no sputtering or anything I could use to diagnose the problem

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