Looking for help confirming that the voltage measured at the ECT should measure ~5v? I know the ECT gets its reference voltage from the VCM which it uses to communicate. My TSM states the same (using a 5v reference from VCM). To be clear, I am not referring to voltage being communicated, but rather the raw feed from the VCM to where it first enters the ECT. I back probed and got less than 2.5v. Just need to insure there is a problem and its not a matter of the VCM correctly sending less than 5v? Can anyone confirm my thoughts or shed some light?

 

Not the way to test anything with the coolant sensor. Sometimes sensors pull reference voltages down and this is how they work. Just monitor coolant temp with a scan tool. With the coolant temp sensor plugged in it should read actual coolant temp (ambient if car has not been started).

 

Probably wasn't clear. Not working on the ECT... I'm testing the wiring looking for excessive resistance, shorts or opens in the entire circuit, to include the VCM.

But I did find my answer and wanted to share for the good of the order. My thoughts were incorrect. The voltage measured by back probing the feed wire is indeed supposed to reside around 2v. This also showed the same voltage when measured using my Autoenginuty tool. Once I disconnected the sensor...voila! The feed wire now showed my 5v reference coming from the VCM

 

What I described will do exactly that, plus test the sensor itself. If anything is wrong then scanner doesn't see correct temp. If it does see correct temp, then the sensor + all wiring in the entire circuit is OK. Any problems in the circuit will skew the temp reading the VCM sees to the wrong value. Simple as that.

 

What you described did not answer my original question. Readings at the DLC are only half the story. The scan tool will display the info it gets from the DLC. However, the ECT circuit information can be skewed due to several reasons and the scan tool will not know this. As we know, it is reporting information it is getting from the VCM on the ECT circuit. As stated in my original post I was not seeking the volts the VCM was reading, but rather the proper volts that the VCM should be putting out from the reference wire to the ECT sensor. You answered that was not the way to check anything with the ECT. Actually, though that wasn’t my question, that is incorrect also. The TSM specifically takes you through steps of measuring the feed line and return line when you have low and high voltage ECT DTCs. There are other checks and repairs before it gets to “replace the sensor”. (Brain dead me didn’t find it until after I had posted my question).

Since it is entirely possible for an ECT circuit to be out of range and not set a DTC...is it out of range because the ECT itself is faulty? Or is a “dirty” or erroneous 5v reference voltage from the VCM, or excessive resistance in a wire, a bad connector, a loose pin at the VCM, is the TPS causing a problem since it and the ECT share a return wire, etc, etc? Simply plugging in a scan tool is not going to answer those questions and seeing ECT volts and temp is no guarantee that all the wiring in the circuit is OK.

It is correct to say that any problems will skew the temp reading to the VCM. But that may be the issue. It may not be adjusting for optimal performance (no DTC set). The trims could be off enough to really effect performance and fuel consumption. For example, “A skewed sensor could result in poor driveability conditions.” (TSM). It is “garbage in, garbage out”. Though I knew it was a primary sensor and had a large effect on trims, it’s actually more than I and probably most people would think. Which is why I was running through the whole circuit and not just relying on the scan tool giving me a thumbs-up

Regardless of whether the data is skewed enough to set a DTC or not, the scan tool will tell you some things, it will not tell you “There is higher than normal resistance in the yellow wire due to corrosion which is adjusting the voltage the VCM is computing. Replace the wire”.

 

Seeing the correct ECT temp using a scanner DOES verify the entire circuit including reference voltage, sensor, wiring, and connectors are OK. I'm done with this. Sorry you don't like my answer.