Intermittent ECT Troubles

At my wits end with 2002 Z06, need some help please. Problem began with Check engine light. warning alarm and "Engine Coolant Overtemp" indication after a 50 mi. trip with no issues but occured immediatly after start returning home. I removed and replaced the ECT sensor (from GM dealer) and for several trips had no faults then it came back and has haunted me every since for about 3 months. It appears to be intermittant and I have accomplished the following steps in troubleshooting:
1) R&R ECT Sensor (initially ok)
2) R&R Battery (GM Dealer)
3) Disconnected PCM and ohms check point to point wiring continuity and checked for shorts on each (2) wires. Wiggled wires during checks to verify no intermittant issues. All checked good.
4) Cleaned all wire connectors (CAIG Products) even though they did appear to be ok with no visible corrosion or dirt.
5) Disconnected MAF sensor and cleaned pins with CAIG product.

I have looked at the parameters with Auto Tap tester and they are intermittantly good and bad just like the DIC readings.

The temp become erratic and spikes to high readings (sets off protection mechanisims and warnings) although I have seen it swing from high to low (0) temps.

After all this troubleshooting I currently have P0117H code and temp still spikes and sets off protection sequence which can be felt while driving the car as a momentary surge or hesitation.

Fans appear to be working ok and I have the problem with A/C ON and fans running from the startup or OFF and not running at startup.

I was extremely careful when installing the new ECT and torqued as per the manual. It ran OK for several trips with no issues then intermittantly the problem reappeared.

Beginning to think I got a bad ECT from the dealer or the PCM is not doing its job. There are no other codes which would point to any other problem with the PCM other than the fact that some trips it does not occur and others it occurs on/off the entire trip.

Open to any suggestions as where to go from here.

Thanks in advance for your help with this issue.

[c4c5specialist]

HI there,
Replace the connector for the ECT sensor.
Allthebest, c4c5

C4C5specialist, Thanks for your quick response. I am aware of your technical abilities and knowledge from following multiple forums but I find it quite difficult to accept this as my problem. The rubber environmental seal is in excellent shape, and the 2 connector sockets are tight as well. Could you please further explain the rationale for your fix for my edification. I am a technician and troubleshoot/fix fighter aircraft for a living and have seen solutions like this that may not make since unless past experience proves it to be the right thing to do.
Could you please steer me to a place where I can buy the connector and what special tools do I need to R&R the wires. Should I also reterminate the wires with new pins ?

Thanks again for your help, Doug

I have another question, does the PCM input or output (pin 80,74)have a resistor (~350 ohms) in this circuit or does the ECT thermistor provide the only resistance to the PCM 5 volt reference signal ?

[c4c5specialist]

Pin 74 is your voltage OUT to your sensor. 5.0 volts.
The PCM monitors how much voltage is seen taken from it in order to determine actual temperature.
GM does not give you a resistance value, as the PCM should not be tested this way.
Pin 80 is your ground source through the PCM.
That being said, normally, my diagnosis is due to the fact that this code is set from a short to ground on CKT 74, which pulls all the voltage, thus setting the code.
As the sensor wiring harness routes by the alternator bracket, the wiring is rubbed through, creating the condition.
That is why I recommended replacing the harness and using all the connector harness wiring.
There is one other possibility. The harness at the fuel rail crash bracket could have rubbed through.
This is at the REAR of the drivers side fuel rail.
Allthebest, c4c5

Thanks c4c5specialist for your help.

Here is what I did to fix my problem. Pulled the ECT connector and rang the circuit out again. Measured 5.0 vdc on pin 74 and good ground on 80 with vehicle running. Measured 4.2Kohms from 74-80with the ignition off. Pulled the stand off wire cradle attached to the generator bracket and found the wires strapped with 2 wire ties extremely tight from the factory. I peeled back the heat resistant cover and found the wires were sharply bent where they entered and exited the wire cradle so I reshaped the wires, wrapped each individual wire with coiled wire wrap and re-wire tied them loosely but secure. Also found sharp bend in the wire harness at the end of fuel bar (where c4c5specialist said to look) that was rubbing on a bracket but did not appear to be chaffed. I rewrapped that area and located the harness away from the bracket.

I have had 12 successful runs on the car with no issues/codes. Although I'm unwilling to declare victory till I get more runs on the car it appears that all signals are rock solid and behaving well. The car also seems to run better I guess because the ECT signal is now solid and the PCM has a good ECT signal to schedule other parameters.

Hope this info may help someone else in the future with the same problem. Thanks again, this forum rocks.