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I have an 05 5.3 354k miles (original motor) and I’m having what I think is an ecm issue, but I want to be sure. A few months ago it started saying “engine overheated” or “engine coolant hot” and the temp needle on the dash would rapidly go up and down. Another thing it does, but only when you drive the truck cold is that around 45 mph when it says “engine overheated” and the needle goes up, the truck will do a shudder. I’m thinking it may be a bad torque converter. I read up that it goes into an engine protective mode that reduces the power when it’s overheated. I didn’t do a scan then, but I went ahead and changed the thermostat and coolant temp sensor. Then after driving for a few minutes it did it again. I decided to scan it and I had the codes P0327, P0449, P0117, and P1258, with the last two being new ones. From that I decided to change my coolant to make sure there wasn’t any air bubbles in it, but it didn’t work. I then put on a new temp sensor harness after the temp needle stopped working altogether (it works now), but it still says it’s overheating. The last thing I could think of is that it may be the ecm. If it is I haven’t decided if I would get mine refurbished, or get a new one and have the dealer program it for me.
 

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Discussion Starter #2
I forgot to mention it before I posted it, but after putting on the new coolant temp sensor harness only the P0449 code showed, the other 3 went away.
 

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Did you check the actual engine temp when the ECM reports overheating?
Other than what the needle says on the cluster no. It just shoots up to 260 then will go back down to 200. Other than using a nice scan tool, I don’t know another way to get the temp
 

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You need to verify that the temperature is actually changing.
It could be a loose wire, or a bad temp sensor.
 

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Harbor Freight has a pretty decent non contact infrared thermometer for around $29.
 

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so the temp gauge got to max temp then drops to 200F rapid changing THEN the wire to the temp sensor has a short circuit .. when the two wires short then the temp gauge goes to the max..

IF THE WIRES TO THE TEMP SENSOR OPEN THE TEMP WILL INDICATE -40F..
IF you have a low pressure in the coolant system the coolant will boil and the water pump will not pump air bubbles... check the pressure cap or a leak..
 

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Discussion Starter #8
You need to verify that the temperature is actually changing.
It could be a loose wire, or a bad temp sensor.
It doesn’t seem like it is changing, but I need to get a way to make sure. It’s a new temp sensor and a new harness and it still did it.
 

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so the temp gauge got to max temp then drops to 200F rapid changing THEN the wire to the temp sensor has a short circuit .. when the two wires short then the temp gauge goes to the max..

IF THE WIRES TO THE TEMP SENSOR OPEN THE TEMP WILL INDICATE -40F..
IF you have a low pressure in the coolant system the coolant will boil and the water pump will not pump air bubbles... check the pressure cap or a leak..
It has a new temp sensor and when I replaced the harness to it, I drove it around for about 8 min and it acted normal. I was happy and pulling back into my driveway and then it did it again right when I was pulling in with the new wires. For a bit before I spliced in the new wires it wasn’t giving a reading at all and staying at the bottom. How can I check if it has low pressure? Idk if it makes a difference, but back when I was in high school (6 years ago) I had a coolant leak that would just drain it like nothing. I couldn’t afford to keep putting actual coolant in there constantly, but I would put 64oz of tap water (Ik it’s not good) in it every time I drove it. I did that for about 4 months before I could afford to get it fixed
 

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2014 GMC Sierra Z71
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The radiator cap has a spring on the underside and it may be weak and not providing the spring it needs to put proper pressure on the system. Sometimes there will be evidence of coolant leaking out from under the cap.

Check that area. Get a new radiator cap and swap it out for the old one. See if that fixes the issue.
 
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