Hoping for some wiring help on my 87’ swapped with a 2004 5.3 out of a Silverado. It’s wired up using a hawks harness. I can not get the temp sensor to work I’m getting a po118 code and it’s reading out at -38 degrees. I don’t have a 5volt reference at the sensor so I ran new wires back to the ecu. A Haynes manual I have for the truck said it should be pins 42/33. After running new wires I still don’t have 5 volt reference at the connector and it’s still reading -38 degrees. I’m wondering if it’s possible my harness is pinned wrong/ or the manual is wrong. Or I’m just missing something. Thanks in adva

 

Always just got to chase it backwards. You've mentioned running new wires since you didn't have reference voltage at the ends, but did you check that you had reference voltage at the source?

With no real info on the PCM, best I can find is THIS that suggests you're looking at the wrong pin.

 

You don't have a 3 wire coolant temp sensor so you won't have a 5v reference. You have a 2 wire sensor so you'll have a ground and signal. You've got a bad sensor or bad ground. Where in the hell did you get the idea you need to have 5v reference??

 

Probably just trying to sound electronically sophisticated without actually knowing what's going on.

 

I'm not sure this guy is even real. He posted the exact same chit over on ls1tech

 

Yeah, he's real, he gives good, idiot-proof advice, and he says it in a funny/ memorable way.

What do you think the "signal" is?!

PCM sends out 5 volts, it goes through the thermal resistor that is the sensor, and the voltage that makes it through goes back to the PCM, where it is interpreted as temperature. For the record, try "grounding out" that low-reference wire, and see how well that works out for you...

The three wire sensor has that, PLUS 12 volts going to pin C, and that runs the factory analog gauge.

I really wish that we had a "downvote" button on these forums...

Hey OP, this kind of problem is exactly the reason why I don't like aftermarket harnesses.