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Just bought the truck, and P0128 popped up this morning.

1K views 6 replies 3 participants last post by  elementaltoad 
#1 ·
So I bought a 2005 LLY, and I'm wondering if this isn't turning out to be a mistake. I love the truck, but it just threw P0128 this morning while sitting at a stop light on my way to work. (seems like the T-stats are stuck open) The truck has always since I've had it, seemed to run at or below the 1/4 mark, especially on cold days. I've had it for a couple of weeks now, and I just checked the coolant and topped off the other night, it was about a 1/4 low in the reservoir.

I have come across more than a few threads saying this is the beginning of head gasket issues, is that a common first sign of bad head gaskets? Should I stop driving the truck?

I am going to replace the thermostats tonight and check pressure on the system, as I imagine the dealer will just laugh in my face if I bring it in.

Any advice?
 
#3 ·
That's one of the threads I found. I'm going to check it before I drive it back home during lunch and watch the temps. I haven't noticed any leaks, but I know these pumps like to die right around the 100k mark. Otherwise it appears to be a well maintained truck, so I'm hoping it was never abused with tunes.
 
#4 ·
I checked the hose after sitting over night, it's not hard and i can squeeze it closed fairly easy (makes the overflow tank slosh around). I changed both thermostats refilled and bled the system then took it for a drive. It got up to the quarter way mark within 5-10 minutes so I will see if this fixes it. It's around 40* here right now so if it warms up that quick it should be fine during the day. However, if it idles in the driveway it never reaches 160*. Do these things just run cold?
 
#5 ·
Duramaxs don't build heat at idle like a gasser. As long as it comes up to operating temp driving you're good. I would double check with a cts2 or scanner of some sort since the gauge is just a dummy gauge.
 
#6 ·
I set up my HP Tuners scanner with a config for diesels, since it's all I have. I cleared the codes, and oddly it had a p0700 pending along with the p0128 I had. I took it for a drive and it came up to about 150 and just hung out there, so I flogged it with some spirited entrance ramp entries and got it up to 185* but it just drops off as soon as I let out of the throttle. I came back home and rescanned for codes, and it has another p0128 pending.

We bought this thing used, but I'm tempted to bring it back to the dealer. With less than two tanks of diesel on it, I'm already popping trans and engine codes. Paying that kind of cash for what will amount to a roller truck 200 miles in seems like theft, especially when I traded in the trusty Excursion on it.
 
#7 ·
I did some more scanning and logging. I believe the p0700 was from my "romp" after clearing the computer, and spazzing out the trans before it had a chance to relearn. The shifting is getting much better and I have not had any more p0128 codes pop up over the last two 40-50* days. Now that it is back in the 70-80s, the truck is running right below the 210 mark which seems to be about 180-190 on the scanner. It will sit right between the 1/4 mark and 210 mark when idling for extended periods.

All seems well so far as far as I can tell.
 
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