Temp Gauge at Min - Again!

[GregA]

Hi Folks,

Well it has happened again - the Temperature Gauge went to the far left (minimum) again (2nd time I have noticed) while driving from a friend's house last night. I also noticed that the cooling fans were running on High when I got in the driveway. So this morning I went out and did a couple of tests.

When I started the van, the gauge was still at the bottom of its range and the cooling fans would start running within a few seconds of starting.

First, I suspected that the ECT (Engine Coolant Temperature) Sensor was starting to go bad, so I unplugged the connector to the sensor and made some measurements. With the engine cool (not cold), it read about 1.5 K-Ohms.

Then I started the van again and continued to take measurements of the sensor. Just as it should, the sensor started to read lower & lower values as the engine warmed up for a couple of minutes.

So now I was suspecting a loose connection between the sensor and the PCM (computer). So I examined the sensor connector for any dirt or other problems and it looked OK. I reconnected the sensor.

Since the gauge was still "stuck low" and the fans were still running all the time, I decided to connect my data reader/logger tool and verify that the PCM could not read the sensor. To my surprise, I WAS seeing about 150 degrees from the system and it was going up slowly.

Finally, I checked the "history codes" screen and saw a P0128 DTC. This decodes to something like "Coolant does not reach rated thermostat temperature." So I decided to clear the history code and see what happens.

The next time I looked at the temperature gauge it was back to its "normal" behavior - no longer at its minimum setting. I also looked under the hood and noticed that the cooling fans were off now.

So the system seems to be back to normal, but I do NOT know what caused the history code. It could be my thermostat sticking open sometimes, or it could have been caused when I took the connector off to make those measurements (engine WAS running), or maybe some "other" loose connection.

I also don't know why the gauge would show minimum while the PCM is receiving other values. Strange!

I will keep an eye on the gauge and see what happens in the future.

Take Care,

[clee425]

Originally Posted by GregA

Hi Folks,

Well it has happened again - the Temperature Gauge went to the far left (minimum) again (2nd time I have noticed) while driving from a friend's house last night. I also noticed that the cooling fans were running on High when I got in the driveway. So this morning I went out and did a couple of tests.

When I started the van, the gauge was still at the bottom of its range and the cooling fans would start running within a few seconds of starting.

First, I suspected that the ECT (Engine Coolant Temperature) Sensor was starting to go bad, so I unplugged the connector to the sensor and made some measurements. With the engine cool (not cold), it read about 1.5 K-Ohms.

Then I started the van again and continued to take measurements of the sensor. Just as it should, the sensor started to read lower & lower values as the engine warmed up for a couple of minutes.

So now I was suspecting a loose connection between the sensor and the PCM (computer). So I examined the sensor connector for any dirt or other problems and it looked OK. I reconnected the sensor.

Since the gauge was still "stuck low" and the fans were still running all the time, I decided to connect my data reader/logger tool and verify that the PCM could not read the sensor. To my surprise, I WAS seeing about 150 degrees from the system and it was going up slowly.

Finally, I checked the "history codes" screen and saw a P0128 DTC. This decodes to something like "Coolant does not reach rated thermostat temperature." So I decided to clear the history code and see what happens.

The next time I looked at the temperature gauge it was back to its "normal" behavior - no longer at its minimum setting. I also looked under the hood and noticed that the cooling fans were off now.

So the system seems to be back to normal, but I do NOT know what caused the history code. It could be my thermostat sticking open sometimes, or it could have been caused when I took the connector off to make those measurements (engine WAS running), or maybe some "other" loose connection.

I also don't know why the gauge would show minimum while the PCM is receiving other values. Strange!

I will keep an eye on the gauge and see what happens in the future.

Take Care,

Mine has been doing the same thing for over a year on and off. I have change the sensor and still does it. I keep a code computer in the van. When it happens I clear out the codes and it works great again. Its done it 5-6 times over the year. Cleaned connections on the computer and still does it.

If you find out a cure let me know..

Thanks,
Donnie Lee

[GregA]

Originally Posted by clee425

Mine has been doing the same thing for over a year on and off. I have change the sensor and still does it. I keep a code computer in the van. When it happens I clear out the codes and it works great again. Its done it 5-6 times over the year. Cleaned connections on the computer and still does it.

If you find out a cure let me know..

Thanks,
Donnie Lee

Hi Donnie,

So when & what conditions were present when yours did it?
And where does your temperature gauge "normally" sit?

I first noticed my problem when it was cold out (40-45 degrees) and the temperature gauge was pretty low anyway. Then suddenly - minimum reading. It was relatively cool a few days ago too when I noticed this again.

And both times I was running at highway speeds for a little while before I noticed the gauge being low.

What I think is the problem is that the thermostat is opening too soon, causing the P0128 code because the temperature doesn't get above about 170 degrees when on the highway. Then the PCM freaks out and turns the fans on, probably "playing it safe" - like maybe the temp sensor or wires are broken. I guess it is better to have too cool than too hot!

I want to change the thermostat, but it is kind of a pain to get at.

If someone knows an "easy way" to get to the thermostat, I'm all ears.

Take Care,

[clee425]

Originally Posted by GregA

Hi Donnie,

So when & what conditions were present when yours did it?
And where does your temperature gauge "normally" sit?

I first noticed my problem when it was cold out (40-45 degrees) and the temperature gauge was pretty low anyway. Then suddenly - minimum reading. It was relatively cool a few days ago too when I noticed this again.

And both times I was running at highway speeds for a little while before I noticed the gauge being low.

What I think is the problem is that the thermostat is opening too soon, causing the P0128 code because the temperature doesn't get above about 170 degrees when on the highway. Then the PCM freaks out and turns the fans on, probably "playing it safe" - like maybe the temp sensor or wires are broken. I guess it is better to have too cool than too hot!

I want to change the thermostat, but it is kind of a pain to get at.

If someone knows an "easy way" to get to the thermostat, I'm all ears.

Take Care,

It was running down the interstate on my way home. It seem to be at the 1/4 mark then just dropped to zero like it came unplugged. Pulled out the code reader, did a reset and worked fine. Changed the sensor and the themostat still does it. Cleaned connections same problem. Temp gauge displays are showing just before half way point with AC on, with AC off and warm it will go almost to 3/4 then fans come on. If its cold outside it will sit just before the 1/4 to 1/2 (middle).
Iam hoping to get rid of this thing in a few more months. It was a 2000 WB purchased used from the dealer. Had lots of problems. I patched the fuel connector problem, now the window on driver side will fall down. it has 127,000 miles. I have an 97 ford explorer with the 302 V8 gas mileage is crap but never had a problem. Its got over 180,000 miles on it. The WB Iam affaid to drive it. I don't know whats going to fall off next. Its a pile of garbage that looks good. When I go to the dealer iam going to reset the computer before I go in the show room. Seems that what they did to me. I didn't have it 3 days before problems started and dealer would cover nothing. Had the intake gasket leak, just put bars stop leak in till it stopped, then drained and put the green coolant in it the other day.

[4432flying]

To Greg A There is no easy way, but this is how I did mine. Drain the cooling system, remove the boot between the air filter and the throttle air flow control. You will need to unhook the steel heater tube, at both ends, below the air flow control and then remove the air flow control from the intake manifold. Then you should have no problem removing the thermostat. good luck. Bill

[LMP]

Greg....there are TWO coolant temperature sensors: one for the PCM (2 wires) , one for the gauge (one wire)!!!
Gauge sensor is left side of engine, PCM sensor is TOP left side of engine.

[GregA]

Originally Posted by LMP

Greg....there are TWO coolant temperature sensors: one for the PCM (2 wires) , one for the gauge (one wire)!!!
Gauge sensor is left side of engine, PCM sensor is TOP left side of engine.

LMP,

Do you have a diagram of where those sensors are?

I could be wrong (that happens sometimes), but everything I have seen on my 2001 (3.4L engine) shows there is only ONE sensor, mounted right next to the thermostat housing, that goes to the PCM, and then the PCM sends a signal to the instrument cluster (temp gauge) over a "serial communications link", to display the temperature to the driver.

Take Care,

[LMP]

May be you are right...I have the 3.4 diagrams from a few years before....It would be logical they have evolved in that way

[neoflee]

hey, having aprobs with the fans not turning on, the fuses are good and the coolent temp sensore is brand new. the fans do work cause i ran a hot to them and they turned on.. What else could this be?
[email protected]

['97ventureowner]

Closing this because I see you started a new thread. Thank you.