1999 Zx2 coolant temp sensor

[NHTennis]

I think my coolant temperature sensor (or gauge) is not working properly. After checking coolant levels, hoses, etc, I've narrowed it down to the sensor or the gauge itself. The gauge does not reset to zero after having sat in the driveway overnight. The gauge moves slightly lower, but basically, remains unchanged from where the temp was when the car was turned off. When driving, the temp gauge does move higher..probably the same distance as it would if it were working properly. This at first worried me, because the gauge was creeping towards the danger area.

I have a Chiltons manual, but can not seem to find the page(s) describing where this sensor is located and/or how to troubleshoot. I know if I were to disconnect the sensor, I am hoping the gauge would drop to "cold" when the car starts up. This would most likely indicate sensor problem..correct??

Also, the check engine light or other dashboard warning lights have not been triggered by this particular problem.

Thanks for any input anyone can give.

[jeffcoslacker]

Not quite sure what you want to do, but grounding the sensor wire to the engine (one wire sensor) or shorting the terminals in the wiring together (2 wire sensor) should make the gauge go full hot with the key on.

I'm not quite clear from what you wrote, but when you start the car in the morning, does the gauge go down to cold, and then warm up normally?

I'll have to look at my wife's car when she gets back, see if the gauge drops to cold when shut off, or floats.

[NHTennis]

Thanks for the response.

In the morning, the gauge starts in the middle of the temp range. Usually, after the car has sat for a while, the temp gauge begins at "c" once the key is turned and the slowly moves to normal temp.

Thanks!!

[mr_tw]

so the gauge starts at C in the morning then moves to warm? in my own car (a Taurus) when i turn it of the Gauge "floats", this is completely normal all it means is that when you turn the car off the needle dosent drop, it stays at where it was when the car was last on, example if the car is at the middle of the operating temp then when you shut your car off that what the needle will be at because that is the tempreature of the engine, and when the car is off it stays there because the sensor is no longer sending a signal (if all your sensors stayed on while the car was off you would stand a good chance of killing the battery) then when you turn the car on in the morning it goes to C becaue the sensor is on again and it sends signal to the gauge, if this is the case then you would probally want to get it fixed asap, because if your gauge is reading improperly you could be overheating your engine and doing serious damage, also you could look into the haynes manual, its what i use on my car and has saved me allot of money, well good luck

[NHTennis]

Thanks for your input.

Usually, my car when initally started in the morning, the temp gauge would be at "C". And when driving around, the temp gauge would settle somewhere in the middle.

However, the past couple of days, when I start my car in the morning, the temp gauge begins in the middle, and slowly works its way up to the "H" area--although it does not go into the red danger area. I've checked coolant levels, upper, lower radiator hoses, fan, etc. And, to my untrained eye, everything appears to be working properly with the cooling system.

I am thinking that somehow, for some reason, the sensor is not working properly because right now, my "cold" engine temperature is in the middle of the temperature gauge--that is where things start in the morning now. Since the sensor is a thermistor, a slight change in the resistence over the sensor would give me a false sense of engine temperature from the gauge on my dash.

I'll continue to look into diagnosing the problem.

Thanks!

I currently have an appt. next week with the Ford dealer, and am trying to learn as much as I can before taking the car in.

[jeffcoslacker]

Yeah now that I understand the problem you are right, sounds like unusual resistance in the sesor or gauge.

I went through something similar on a customer's Escort, and after eliminating every other possibility, it turned out to be a defective gauge, and since the gauge was part of the whole cluster, that had to be replaced.

And it was on backorder, D-99. Took six months to get the new one.

[NHTennis]

Jeff,

Thanks for the input. I think it is either the CTS or the gauge. I've measured the resistance across the two terminals of the CTS and compared those values to the ones listed in a Chiltons Manual. The car was driven to work this morning, and then sat for about 4 hours in the lot. I grabbed a voltmeter from work, and measured the resistance, and it was 5.6 kOhms. According to the specs in Chiltons, this would be approx. equal to ~100-110 degs F. My drive to work is about 2 miles. So, I'm not sure if the coolant temp would still be that high. I think my best bet is to wait until the morning tomorrow and measure the resistance afterthe car has sat overnight. This will give me a better indication of the resistance across that thermistor when the engine is truly cold.

Also, when I unhooked the CTS and started the car, the temp gauge on the dashboard stayed put. I thought it would have for sure moved to the cold. This might be an indication of a faulty gauge rather than CTS.

Thanks for any advice. I'll keep posting as I figure out what is wrong.

[NHTennis]

Here's an update :

I tested the resistance of the coolant temperature sensor this morning. The measured coolant temperature from the radiator was 25 degs C (77 degs F), and the resistance in the SENSOR was 27,600 Ohms. And, according to my Chiltons manual, this agrees well with what the sensor should be reading given that temperature.
I then started the car for 2 mins, turned it off, and measured the resistance again, and it read 15,500 Ohms. This resistance equates to approximately a coolant temperature between 40-50 degs C (104-122 degs F). I should mention that I did not measure the coolant temperature once the car was started, but just going on the chart in the Chiltons manual.

I do think that the problem lies in the SENDER unit, but I have yet to troubleshoot that particular device. I'm having a tough time locating it. I looked around the plastic housing where the SENSOR is located, and could not find another connector that looked similar. I will try and look again later.

Thanks again for all the help and input. If anyone knows where the sender unit is located, let me know! Thanks.

[justhere02]

Hello. I have an '02 ZX2 and I can't find mine either. Could someone please help us out?