http://forums.corvetteforum.com/zerothread?id=847842

 

You more than likely have an "open" (or is it a short?) from the temp sensor on the block to the PCM. You must have unhooked, snagged, jiggled or otherwise affected the continuity between these two items. If you have an ohm meter and a service manual, you can fix it. Otherwise, wait for others to chime in with the "short cut" methods. Either way, the readings are bogus, so I wouldn't panic.

 

Thanks for the info. Makes me feel better!
Well I have a OHM meter but I dont have a service manual..
Anyone know the "shortcuts"....

 

If no one responds in a timely manner, I will look it up for you in my factory manuals.

 

Thanks alot buddy..

 

O.k. so you are in luck. The ECT (Engine Temp Control) circuit is very straight forward.

1. Interestingly, it seems a DTC / DIC code is only set upon a too low temp condition / no code for too high.

2. There is a sensor "loop" between the PCM pin 74 on C1 (BLUE connector) to pin 80 on C1 (BLUE connector). Pin 74 is sensor signal-side (yellow wire), pin 80 is sensor ground-side (brown wire).

3. The PCM generates a 5v signal along the loop. Sitting in-line is the ECT sender unit (engine temp sender, located on the LH side of motor, under the generator.) The ECT has a variable resistance across it based on the temp.

4. At the extremes; too cold = high resistance value on ECT = low voltage drop across loop = low degree reading on DIC.

5. As above; too hot = low resistance value on ECT = high voltage drop across loop = high degree reading on DIC.

6. So, it would follow that assuming a non-defective ECT sensor, that a disconnected ECT wire (pulling the connector off of the temp sending unit) would result in a very low DIC temp reading (-20 degrees, for example), and shorting the ECT signal wire to ground would result in an extremely high DIC temp reading (+280 degrees, etc.), i.e. your condition.

7. So the obvious.. Trace the ECT wire in the engine bay, pull it off of the ECT. The DIC should read a very low temp. If it doesn't, bingo, you have a portion of the ECT sensor wire touching ground somewhere.

If the DIC does go low, then maybe you do have a "bad" temp sensor, although I'm not sure how common that is. You might want to try and measure the resistance between the two terminals on the ECT, to see if it's a dead short.

8. Based on your previous statement that recent engine work was performed, I can only assume the possibilty that the temp sensor wires are pinched / ECT unit damaged somehow.

9. Good luck, let me know if you have any other Q's about this.

 

Thanks for all your help.

But something wierd happened. I started the car up today and the gauge was working. Drove it around with no problems.. I have no idea how it fixed it self. Maybe it needed time to just recalibrate
Oh well, but all is good. Thanks again for helping me out quickly if I did have the problem.

 

Hey CraZee,

Too bad your engine wasn't running hot. I'd have made some beef's on a stick and brought them to ETown tomorrow and "cooked them" on the engine for you.