89RsPower!

1989 Iroc 350 tpi. I'm having an extremely annoying problem with my coolant temp sensor, I'm not sure where to go from here, maybe someone can point me in the right direction. The problem is basically this, the reading is always too low (voltage reading too high). It operates in the proper way, that is voltage starts out high and slowly lowers as the car heats up, the problem is it never gets low enough for the fans to operate. At 240 degrees the voltage reading is around 1.5 volts. I've tried several different sensors, all with the same results. I tested the wires from the connector to the ecu, they both ohm out at .4 volts which leads me to believe they are ok. I've tried a different ecu (with the same prom), still same results. The only thing I can think of is maybe I have a crappy ground somewhere, does anyone know where the ground is located? Is there anything else that could be the problem? This thing is driving me nuts, I just want to be able to drive the piece of **** without it overheating and bogging off idle..

Viprklr

iTrader: (5)

What are you using to seal the sensor to the engine?
Sealant with Teflon seems to be the sealant of choice. It's apparently ground friendly.

Look in your repair manual for an ecm pinout/schematic. That should show you the ground. There's probably one on this site somewhere.

89RsPower!

Yeah, used teflon sealant on a couple of the sensors, one of the others came with some sort of lock tight on it. Anyway thats defently not the problem.. I know where the pinout for the ground side is and it ohms out fine, I'm assuming there is a ground point for it somewhere but I have no idea where.. hopefully someone will have some insight into this or at least know where to find the ground..

Viprklr

iTrader: (5)

According to the schematic there's a ground at the ECM and the sensor grounds on the engine. That's it for the grounds on a CTS.

89RsPower!

Hmm well that sucks.. haha hopefully someone will have some insight.. there has to be some explination... what would cause it to always read way colder then it actually is..
Another strange thing worth mentioning is that if I take a CTS and hook the connector up to it without installing it but sticking it between heater hoses and in a sense using it as a probe it reads the correct voltage/temperature until it reaches .94 volts where it suddenly jumps up to about 3.6 volts.. Can't pretend I have any clue how to interpret that but maybe someone else does..

89RsPower!

What I'm wondering is where that ground is physically located. The ecm it self as far as I can tell isn't grounded to anything, it mounts to a plastic mount which mounts under the dash which leads me to believe that there must be a ground through one of the wires that run to it through the harness. Also does anyone know if polatiry matters on the sensor? Would any damage occur if it was wired with the polarity reversed?

DENN_SHAH

iTrader: (1)

polarity of the CTS doesn't matter.

i believe what your seeing with the CTS volts jumping up is part of the way GM set it up.
on some systems there is a switching transistor in the ECM that once the engine has ran for so long, the transistor switches and you see the change in the voltage.
IIRC, GM did that for a more accurate reading from the CTS during warm-up.

about the grounds,
D2 at the ECM shows to be the ground for the CTS, TPS and the MAT.

A12, D1, D10, and D3 show to be ground for the ECM.
D6 shows to be the O2 sensor ground and ties in with the other ECM grounds.
G112 and G118 are grounds for the ECM.
there are many things grounded thru G112 and G118.

the blower motor, high speed blower relay, and A/C control head go to splice S112 and then to splice S185, then to ground G112.
the compressor clutch and wiper motor module go to S185.
there are several grounds from the ECM that go to splice S143.
also going to S143, the fan pressure switch, the MAF relay, and the fuel pump relay.
there is a ground from the instrument cluster, pass key module, ALDL connector, and gear selector switch that goes to S217, and then on to S143.
splice S217 shows to be instrument panel harness behind the center of the instrument panel.
splice S143 shows to be in the engine harness in the right hand side of the dash.
G112 shows to be on the back of the left head.
G118 shows to be on the back of the right head and also has a braided ground strap that runs to the body.

89RsPower!

turns out I have another problem. I hadn't thought to recheck if the fans even worked still so I did that today. Guess what? They don't. When I ground out the aux fan switch connector the relay clicks but nothing else. The fuse is apparently good but no power is going to either fan. Both fan motors are good however as they work just fine when I jump power to them. ideas?