Temp gauge not working and Check Engine Light on.

Ok......2006 LaCrosse/ 3.8L/80,000miles.

Today I noticed that the temp gauge stayed all the way cool and the check engine light came on. I looked at the two wire sensor under the thermostat housing and checked 0V on one wire and 1.55 V on the other when connected. When disconnected I had 4.65 V on one wire and 0V on the other. The resistance was 290 ohms across both wires going to the sensor. I assumed there was only one temp sensor feeding both the computer and gauge? Is this right?

What do you all think? Sensor bad? Is there an easy check to see if the sensor is bad? I have tried to find some scale showing me the resistance/deg F nut no luck.

Anyway....thanks guys

I'm not 100% on your model, but a lot of vehicles have two separate sensors. One for the gauge, and one for the ECU.

according to my chart, 287 ohms is equal to 85C, which is 185F.....

So 290 ohms would be about 183F.....

Would like to see live data vs the gage data...

Was P0128 set?

I have had cars idling in the bay in the garage where it is warm, and the needle slowly moves up to normal......but go out on the highway and it drops immediately(especially in this cold weather).......fix, thermostat...

according to my chart, 287 ohms is equal to 85C, which is 185F.....

So 290 ohms would be about 183F.....

Would like to see live data vs the gage data...

Was P0128 set?

I have had cars idling in the bay in the garage where it is warm, and the needle slowly moves up to normal......but go out on the highway and it drops immediately(especially in this cold weather).......fix, thermostat...
Thanks....Where did you get chart?
I can't imagine thermostat because the needle on gauge was set all the way on cold. Even when I drive the car without a thermostat (which I did at one time for about a month) the needle came up to about 1/4 gauge. BTW...I'm in the Keys so it's 75* down here...

Ok....found the chart and everything looks good with resistance checks at certain temps. I checked for input voltage supplied to ECT and it had about 4.9V...which I assume is correct. I also scanned the codes and they were P0116, P0115, P1116, etc.. they all indicated ETC problems.

After these checks, the gauge is starting to work now. I assume a loose or dirty connection that I "repaired" by fiddling with it BUT the engine light is still on. I disconnected the battery for 20 secs. and the engine light still stays on. I guess I'll have to go to the store and rescan my codes now....

On a side note...I noticed when the temp gauge stopped working, I noticed that the Voltage information on the digital instrument cluster only read 12.8 V. I put a meter on alternator output and it was a normal 14.8V. So there was a big discrepancy. Now that the temp gauge started working, the Voltage reads 14.8 on the instrument LED cluster, which matches my meter perfectly....

Thanks

That's why I would like to see live data vs gage data...possible cluster or connection problem....

That's why I would like to see live data vs gage data...possible cluster or connection problem....
What do you mean "live vs Gauge" data? Thanks

Data from a scan tool, to compare to the gage....

Data from a scan tool, to compare to the gage....
Ok...the gauge stopped working again. I don't have a scan tool right now but I used my temp gun and checked the resistance on the ECT sensor. The resistance matched the temperature pretty close. The temperature is 192*F and the resistance is 228 ohms. This tells me the sending unit seems to be working ? Any other ideas? Thanks

When you checked the voltage on the wires, how did you do this?

Did you attach meter to ground, and with harness disconnected, touch each lead one at a time? In this scenario, you would get the voltage readings you got...

Did you connect both leads to each wire in the harness? Doing it this way, you should have got around 5.0 volts, but if you got 0.0 volts, that means there is an open in either wire......when you do this test, you should flex the harness wire to see if the voltage drops, indicating a bad connection/open wire....

When you checked the voltage on the wires, how did you do this?

Did you attach meter to ground, and with harness disconnected, touch each lead one at a time? In this scenario, you would get the voltage readings you got...

Did you connect both leads to each wire in the harness? Doing it this way, you should have got around 5.0 volts, but if you got 0.0 volts, that means there is an open in either wire......when you do this test, you should flex the harness wire to see if the voltage drops, indicating a bad connection/open wire....
I attached one meter lead to one wire at a time with the other lead to ground. I figured 5V was the correct incoming reference voltage used to drop across the varying resistance of the sensor.

That's true but if the ground circuit isn't tested, there will be no signal to the PCM........an open circuit is high resistance which results in a low coolant data reading....

That's why I would attach both leads to the harness, key on, engine not running, and watch the meter for a voltage change from 5.0 volts as you flexed the both wires......

Ok...to recap.....basically, every once in a while my temp gauge stops working (all the way to left) and my computer throws a P0115 code. Here's the thing.....I hook up my scan tool and read that the ECM is showing the correct temp but the gauge still doesn't work. As soon as I clear the fault the gauge starts working and the Engine light goes off.

Is this normal? Does a temporary fault glitch kill the output to the gauge and does it require a reset to get that temperature data flowing to the gauge again? Thanks

Anyone?

You can answer your own question, by disconnecting the temp sensor, the code will set and the gage should go to low........now reconnect(do all this without shutting the engine off).......

The problem could be the sensor, or either line to it from the PCM....or the PCM itself, which is very unlikely....

You can answer your own question, by disconnecting the temp sensor, the code will set and the gage should go to low........now reconnect(do all this without shutting the engine off).......

The problem could be the sensor, or either line to it from the PCM....or the PCM itself, which is very unlikely....
Thanks.....but I'm not asking how to troubleshoot this...I petty much have it figured out. I am just wondering if it is normal for an intermittent glitch that causes a p0115 fault will cause the gauge to stop working until you actually reset the fault........even when the temperature is accurately reading in the ECM? Just seems weird that it would be programmed to disarm the temperature gauge until someone hooks up a scan tool and resets the fault even when the ECM is reading he proper temperature.