I bought this car a month ago and it was running good till it started getting cold and gave me hard starting issues along with a check engine light. I found that my coolant temp sensor on the water pump wire was cut so I fixed the cut and that fixed the hard starting and check engine light but now the car will overheat and will not turn on fans unless I disconnect the sensor. I’ve already replaced the sensor itself and it didn’t fix it. Any help is greatly appreciated.

 

What temperature do you consider “overheating”? The fans don’t turn on at low speed until the coolant reaches 226°F, then go to high speed at 235°F (stock programming). When you disconnect the coolant sensor the PCM should set DTC 15, and turn on the fans.

The problem with the coolant temp sensor may be related to your cold idle problem, in your other thread.

 

Did you ever follow up with the low oil pressure problem you posted previously?

 

I decided to leave the low oil pressure alone it hasn’t thrown the check gauge light recently and when it did there wasn’t any knocking or anything so I don’t believe there is no oil pressure. Secondly for me overheating is going in to the red zone.

 

Then you need to test the coolant temperature sensors and the reference voltage being supplied by the harness. Sensor in the water pump may be faulty, or wiring is faulty. Sensor for the gauge may be faulty.

Here's the procedure:

4th Gen LT1 F-body Tech Articles

 

The gauge sensor and coolant temp sensor climb up to 18 megaohms then the reader went blank so I’m guessing it maxed out since it only goes to 20 megaohms. What does this mean? And maybe I mixed the black and yellow wire up. Do you know if the yellow is to the right or left of the connector?

 

I had to get a new pigtail since previous owner cut it

 

If I’m correct the yellow wire is on the right side of clip and the black is on the left

 

Turns out the voltmeter goes up on resistantance by itself, like if I touch the two leads and pull them apart it climbs to 19k then back to zero. Should it do this? Idk much about resistance

 

The harness leads for both tested good coolant temp sensor being 4.8 ish volts and the gauge sensor being close to battery voltage about 11.5 ish

 

PCM sensor in water pump should be closer to 5.0 volts. That is the regulated reference voltage supplied by the PCM. Anything less could throw the temp reading off a bit, not much.

Touching the two volt meter leads together should show 0 resistance or very close to it, or "low" for being off scale. Take the leads apart and it should show infinite (off scale) resistance, or the max reading of an auto-ranging meter. Mine shows ~11 meg ohms.

The PCM sensor connector should be labeled "A" and "B". Black comes from PCM pin B6 and connects to "A", Yellow comes from pin C25 on the PCM, connects to "B".

 

So when I use 2k ohms I get 1.95 for the coolant temp sensor and 1.46 for the gauge sensor. I multiple these by the 2k measurement right? So 3,900 ohms for the coolant temp sensor and 2920 ohms for gauge sensor

 

So that would be 74ish degrees at gauge and 64ish at coolant temp sensor right?

 

2K simply indicates the range of the meter on that setting. 2K is not the multiplier.. You are working in units of k ohms = 1,000 ohms. Multiply the meter reading by 1,000, not 2,000.

You have to test the resistance for known temperatures. There is no guarantee the sensor in the head will read the same as the one in the water pump, unless the engine has not been run recently and is stone cold. Then they might be similar.

Inconvenient as it may be, remove the sensors. Immerse them in a bath of ice floating in water. Should read 32°F. Then immerse both sensors in a bath of boiling water. Should read 212°F at sea level. If your location's elevation is significantly above sea level, you need to look up the temperature of boiling water in a table like this (scroll down to table below graphs):

https://www.engineeringtoolbox.com/b...de-d_1344.html