Temp guage malfunction

Help.....2001 venture 3.8 liter. On roadtrip noticed temp guage was showing just a bit above cold mark. Later on it was not registring at all. Heater was working fine. After getting home checked coolant level found that they were ok. Thought it might be the sending unit, but would this not trigger a fault code and sevice engine light. I need a direction to go here from all the good readers out there. Thanks in advance.:runaround:

My understanding of how the temperature gauge arrives at a reading is as follows:
1. Engine Coolant Temperature (ECT) Sensor reads coolant temperature
2. That reading is transmitted to the ECM
3. ECM 'reads' that signal, then sends a corresponding signal to the temperature gauge.
4. Temperature gauge 'reads' the signal from the ECM, and the needle moves to the proper position.

That being said, possible failure modes for a temp gauge that appears to be totally inoperative could be:
- ECT Sensor is shot - does not read temperature correctly
- ECM malfunction - some problem in how the ECM decodes the signal from the ECT and translates it into a signal to the Temp Gauge
- Temp Gauge malfunction - temp gauge does not correctly translate signal from ECM into the proper needle position

I'm going to say the most likely culprit would be the ECT Sensor. And to my knowledge, a faulty ECT Sensor would not turn on the CEL, as it is not sensing any kind of Emission Control condition that would cause OBDII to set a code and turn on the CEL. Just based on my knowledge and experience.

The Haynes manual for my 98 Venture explains simple procedures to test the ECT Sensor and the temp gauge. I used these procedures to qualify each as OK or bad when my temp gauge was floating all over the place (ended up being air entering my coolant system through a bad head gasket).

I hope this helps!

Help.....2001 venture 3.8 liter. :
As far as I know the Ventures only came with a 3.4 engine.

goto autozone or other parts store and get code read. with symptoms you have, will bet it may be a P0128, and that means you need a new thermostat. the following are codes that can be set by the ECT. If the ECT is faulty, it can cause the vehicle to remain in open loop and thus effect emissions and so on.
P0115....Engine Coolant Temperature Circuit
P0116....Engine Coolant Temperature Circuit Range/Performance Problem
P0117....Engine Coolant Temperature Circuit Low Input
P0118....Engine Coolant Temperature Circuit High Input
P0119....Engine Coolant Temperature Circuit Intermittent
and then the beloved: P0128....Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). point is to get it scanned and post back here, guessing at what is wrong with an OBDII system is futile. codes point the way to find the real problem.

kospotts , when you get the new thermastat get one made in u.s.a. if you get one made in mexico your gonna be pulling it back out. as a couple years ago i changed thermastats in mine i just went and grabbbed one stuck it in temp gauge went nuts , heat then no heat, pulled the thermastat out went back got another different brand put it in same thing. pulled it out and so on for 8 times i got to where i could put the thermastat in half asleep and watching tv . 8th time i dropped the brand new thermastat in boiling water it never opened. then i got to thinking all of them had one thing in common---- made in mexico. went all over to a bunch of parts stores and each time they would lay one on the counter made in mexico and i would ask them you got one made in usa and they would reply nope.i finally found one made in usa at carquest and boiled some water dropped it in and low and behold opened like it should. i learned a lesson that i won't ever forget a thermastat made in mexico isn't worth the time spent stamping it in it.