Mal code 15 Coolant Temperature Sensor Circuit

GNICETRY

Cat&wife post starter
Make a long story short, new (Highway Stars) ECM. New Caspers Pigtail for ECM. Getting a code 15 and it is reading -39 on Scanmaster. With the old ECM it is reading the same -39. AND before anything was changed it was reading -39. Wire at CTS (green/black sensor on driver's side) tests at 11.9V. When the wire is wiggled it stays at 11.9V. Old CTS ohmed out and was no good. New AC Delco sensor does not ohm out and tests OK. All grounds were checked and are good. Car is at the mechanic and I am getting this second hand and do not have access to the car.
It is not rocket science here, it is either the ECM (very unlikely), a ground issue (checked) the CTS (again very unlikely) or the wiring? Correct?
Can I just run a jumper wire from right off of the CTS sensor to the ECM CTS pigtail? That would eliminate any wiring issue?
 

GNICETRY

Cat&wife post starter
I asked him specifically the 2 wire sensor on the driver's side and he said yes. But he definitely said whatever wire (I would guess the yellow one) was getting 11.9V. It should only be getting 5V???
I will have to go there to verify.
I replaced the connector to the sensor to get rid of the code.
I will have to order one from Caspers tomorrow.
 

salvageV6

Daily Driver
The coolant temp. sensor has a 5V yellow feed as Eric mentioned and a ground wire from a shared spliced dedicated ground wire to the ECM with the TPS sensor and the MAT sensor. Easy to check and test not something you want to rewire without knowing exactly what is going on.

The green one wire high speed fan switch, and green one wire over temp. coolant indicator will both read battery voltage through the Ignition switch until the simple internal sensing switch is triggered to ground at the respective water temps. of about 220 and 240 degrees then that wire will read to ground to trigger the high speed relay and light the lamp in the dash.

Most likely they are reading voltages that are correct and on the wrong "sensor" when doing the readings.
 

salvageV6

Daily Driver
If you short the two wires in the coolant temp. sensor together the yellow and the black, key on, the scan tool should read a temp. of 210 degrees or more. That would be my first test.

-39 is an open circuit meaning bad sensor or bad connection to the sensor from the harness connector as mentioned, or at the ECM, worth double checking the splice work and connections,
 

GNICETRY

Cat&wife post starter
That should help them. Thank You.

So I stopped by the shop today and with the ignition only on the ECM (both my old one and the new Highway Stars one) were showing 11.9V at the CTS prong on the ECM. Go to the yellow wire at the sensor and 11.9V. I know it should only be 5V. When the car was running the ECM CTS prong and the yellow wire at the sensor were both 1.7V. I saw it. Told him to check the splices again because that is crazy. I am too frustrated at this point and they assured me that they would find the issue and fix it. I will pass the Code 15 diagnostics to them.
If you short the two wires in the coolant temp. sensor together the yellow and the black, key on, the scan tool should read a temp. of 210 degrees or more. That would be my first test.

-39 is an open circuit meaning bad sensor or bad connection to the sensor from the harness connector as mentioned, or at the ECM, worth double checking the splice work and connections,
He connected the yellow and black wires and the temp was still -39 on the Scanmaster.
 

salvageV6

Daily Driver
C12 is the black/yellow factory harness wire that runs inj. #6, if that wire got swapped into C10 for the coolant temp. signal it would read battery voltage +12 through the injector harness power.

And it's only 2 slots away....

The Caspers splice doesn't use the factory colors for the injector wiring, so it can get confusing without an accurate chart made up first of what color on the splice goes to what color on the factory wiring.
 

GNICETRY

Cat&wife post starter
It is fixed!!! The CLT temp sensor wire which should be C10 was in the C9 spot on the Caspers pigtail.
Thank You all so much for the help. Now on to my manifold situation. LOL
 
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