Coolant temp sensor gauge maxed out?

DALTONTROTTER

MEMBER
2004 CHEVROLET SILVERADO
5.3L
V8
4WD
AUTOMATIC
320 MILES

I had to replace a gasket for my exhaust manifold and unplugged my coolant temperature sensor sensor and after I was finished I plugged it back in. I turned the ignition on and the coolant temp gauge was reading maxed out even tho the truck was cold. I unplugged the sensor and same reading on the gauge. Truck is throwing a p1258 overheating code and dash is saying limp mode overheating. I inspected the wires all the way to the y and they look good. I replaced the sensor and nothing changed.

Saturday, January 10th, 2026 AT 7:38 PM

6 Replies

KEN L

MASTER CERTIFIED MECHANIC
55,009 POSTS

So it sounds like the electrical connector to damage or one of the pins in the connector is pulled out of the connector so the connection of the gauge (PCM) is open which will cause this problem, please remove the connector and use a flashlight to inspect the pins.

P1258 - Engine Protection Mode Active

This is normal when the coolant temperature sensor circuit is open. If it looks okay let do a hard reboot of the PCM/Gauges which can help reset the system. Please go over this video.

https://www.youtube.com/watch?v=INiDRO5A5MY

Please go over this guide and get back to us. Please upload a short video in your response of the problem, so I can see what's going on :) Ken

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Sunday, January 11th, 2026 AT 10:51 AM

DALTONTROTTER

MEMBER
9 POSTS

Ok I did what the video showed I’m going to let it sit for a few minutes but the pins in the plug look good and the sensor looks good to

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Sunday, January 11th, 2026 AT 12:34 PM

DALTONTROTTER

MEMBER
9 POSTS

I just plugged the sensor back in and put the negative terminal back on and it did not fix the problem

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Sunday, January 11th, 2026 AT 1:22 PM

KEN L

MASTER CERTIFIED MECHANIC
55,009 POSTS

Yep, something must have got pulled on the wiring you are going to have to test the wiring from the sensor to the PCM. Here is a guide and the wiring diagrams so you can run the test. Also, check the engine harness grounds, if one of the grounds is off it will cause this problem.

https://www.2carpros.com/articles/how-to-check-wiring

Check out the images (below). Let us know how it goes

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