Temperature Reads "---"

[Robinjo]

Fixed (Issue 1):Just needed an Ambient Temp Sensor. For some reason I thought the plug would read it. We all make stupid mistakes, this one is pretty dumb.
Fixed (Issue 2): Temperature read out at -40 degree F. This ended up being the Engine Temperature Sensor on the head. I actually had to get 3 units to get one that worked properly. I did check the wiring, got continuity between the ends and the ECM #2 connector and am getting 5v to the plugs 'hot' wire.

I asked this question in my build log, but making a formal spot for others that may have a similar issue in the future. Symptoms listed below, please add any information you might have here instead of my build log.

Symptoms
-Temperature on Tachometer does read, it did before stripping the Cobalt
-Return button does not work on button panel (may or may not be related)
-When plugged into Torque Lite I sometimes can see temperature and sometimes cannot.
-Cannot see Ambient Temp
-Randomly get "Reduced Power Mode" error (may or may not be related)

Things I've Done
-Replaced thermostat
-Replaced temperature sensor
-Cried and yelled

This is the star of the discussion in my build log as well (posts #164-172)

Robinjo #405 Full Cage - 2006 SS/SC Build "Drago"

It might have just been who I got. The lady next to her eventually had to help guide through the process. In the end, they got it done.

dfkitcar.com

 

[Robinjo]

Items to try from Ross

Robinjo #405 Full Cage - 2006 SS/SC Build "Drago"

It might have just been who I got. The lady next to her eventually had to help guide through the process. In the end, they got it done.

dfkitcar.com

Items to Try from GoblinFanClub1234

Robinjo #405 Full Cage - 2006 SS/SC Build "Drago"

It might have just been who I got. The lady next to her eventually had to help guide through the process. In the end, they got it done.

dfkitcar.com

Robinjo #405 Full Cage - 2006 SS/SC Build "Drago"

It might have just been who I got. The lady next to her eventually had to help guide through the process. In the end, they got it done.

dfkitcar.com

 

[Robinjo]

Swapped out to a 2nd new unit and the --- is still present. However, with this temperature sensor, it gives me a reduced power mode consistently. It could be coincidence but this began after swapping to the new (2) sensor. I'm going to revert back to the new (1) and see if that helps there.

 

[D&dgoblin69]

I’d start by pulling the engine coolant temp sensor connector off and looking at connector terminals. Does the connector have any signs of burnt or melted? Then replace ect connector with new pigtail

 

[D&dgoblin69]

Do you have a scan tool to see data? Do you have a dvom digital volt ohm meter?one last thing before testing. Disconnect the ecm connectors and lock back in sometimes connectors are not fully seated. Your ect sensor gets a signal and ground from your ecm

 

[Gtstorey]

Are you talking about engine coolant temperature (etc) or ambient temperature? You mentioned both in your earlier post.

 

[Robinjo]

Are you talking about engine coolant temperature (etc) or ambient temperature? You mentioned both in your earlier post.

Ambient Temperature issue has been resolved. It just needed a sensor attached to the plug. This did resolve the "---" on the dash.

However, I also am not getting coolant temperature on my ODB-2 connector. It read -40 oF. I've swapped out sensors and have ordered a new plug to install. Should I be getting voltage to the plug with the engine running?

 

[Gtstorey]

This is probably part of the reason that your fuel mileage is low since the ECM doesn't know the car gas warmed up.

I'd have to read the diagnostic procedure to see about voltage reading. I don't think so since it is likely measuring resistance. You need to check the resistance of all of your sensors to see if they are the same at the same temp or look up the correct resistance for your sensor on alldata. Then check and see if you get the same resistance at the pin or pins at the ecm with it plugged in. There are really only three parts to this, the sensor, the wiring and the ECM.

 

[Robinjo]

I watched a video about reading Ohms on it and will be doing that. I have changed the ECT Sensor and the Thermostat during the whole 'no start' issue. That was trying to fix the "---" issue and were easy things to replace. Those are what the internets said the issue would be, but it assumed I had an Ambient Air Temp sensor installed.

I'm not sure where the wires go to the ECM. I've looked at AllData to try to figure it out. I'll keep searching but these schematics are a bit confusing.

 

[Robinjo]

Found this, but I'm not sure what it's telling me.
One is going to PCM C2 - 52
Other is going to PCM C2 - 35

 

[Robinjo]

I think it wants me to go here?

 

[Ross]

You have figured it out! The yellow dot is pin 35, and the red dot it pin 52.

 

[Gtstorey]

And that is looking at the wire connector from the side that is towards the pcm.

 

[D&dgoblin69]

The powertrain control module (PCM) applies 5 volts to the engine coolant temperature (ECT) sensor circuit. The sensor is a thermistor which changes internal resistance as the engine temperature changes. When the sensor is cold, internal resistance high, the PCM senses a high signal voltage and interprets the voltage as a cold engine. As the sensor warms, internal resistance decreases, the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.

 

[D&dgoblin69]

35-2 52-1 what that wiring diagram is telling you is the ect engine coolant temp is reporting to the ecm coolant temperature. Your - - - is default ecm doesn’t know temp hence the reduced power. It’s trying to keep you from potentially overheating . rule out the harness with a resistance check ecm to ect . Ecm 35 to ect 2 resistance check should be about .3 ohms and ecm 52 to 1 should be .3 ohms. Becareful probing the ecm and ect terminals you don’t want to push a test lead to big can cause terminal to spread bigger then the pin of the ecm ect. You just need enough drag when pushing test probe in. if you get a open ol in one of the resistance test you can in splice in a new wire or pull on suspect wire. A open resinstance reading is a broken wire when pulling on suspect wire with enough finesse you will feel wire stretch because your only pulling on the plastic aka insulator

 

[D&dgoblin69]

You got a list of codes?

 

[D&dgoblin69]

i keep saying ecm i forgot it was pcm back then but same thang. On the wiring diagram for reference ye is yellow and bk is black so you can verify your on the right wires

 

[Robinjo]

The “—-“ issue has been fixed. It was the Ambient Air Sensor

The no coolant temp through my OBD scanner and Torque app is also resolved. I finally got a Engine Coolant Temp sensor that is good. I also checked that I was getting continuity through the sensor plugs and points 35 and 52. Also, with the engine running I get 5v to the yellow wire side of the plug.

So, both issues are now resolved. Thanks everyone for your inputs.