Temp Sensor help, please

[chef_tim]

Hi all, got the CCR long block and it runs great. I only have one small issue. When I put the motor in the only thing I didn't hook up was the temp sensor. The cooling fans come on at start-up and it is running very rich (apx 13mpg w/the trailer) I plugged in the sensor and had Auto Zone clear the computer, code 117 "low voltage to temp sensor". the fans went off, but about 30 seconds later the fans came on and so did the CEL. I am assuming that it is the same sensor. Is there a trick to getting it to stay off??? Thanks for the help, Tim

[Cougar]

The best thing to do Tim is measure the resistance of the disconnected sensor and see what it is. If the resistance is real low the sensor may be bad. There may also be a wiring problem to the sensor causing a low voltage to it. You could try substituting the sensor with a resistor that would be the proper resistance of a warm engine. If the problem is cleared then the sensor needs to be replaced. I'm sorry I can't give you any specs on the resistance. My manual doesn't give any. Also check the resistance of the sensor leads to ground. They should normally be isolated from ground I think.

 

As a science project you could measure the resistance of the sensor as the engine warms up. Record the cold reading and then record the warm reading. You should see a pretty good change in resistance between the two readings if the sensor is good. Remove the sensor connection before measuring the reistance of the sensor.

[Olnick]

Wow, Tim, I feel for you. You must be dying to get out on the open road with that beautiful new engine!

 

Did you put a brand new sensor in or re-use the one that was in the old engine? Is the electrical connector clean and tight? Wire look okay? Listen to Cougar--he's the electrical wizard!

 

Guess it's time to go back to Autozone and make sure it really is the same code.

 

Wish I could be more help but I'm sure you'll track it down. Good luck.

[chef_tim]

Thanks Glen, unfortunatly I have no idea how to measure the resistance or for that matter any thing else you recomemded:confused: . It is true, when it comes to electronics I am a complete idiot. I have a multi-meter but about all I know how to do with it is see if the alt is charging. Could you give me some details, and I'll give it a try.

 

I'm not sure if it matters, but the guage works the same as it did before the motor came out. Thanks, Tim

[Cougar]

Tim,

 

I did see one note about resistance in my manual. It stated that measuring one of the pins (pin 2) of sensor with the ignition off should not be less than 5 ohms to ground. It looks like my idea of being isolated to ground is wrong. The sensor is bad if the reading is less.

[Cougar]

Thanks Glen, unfortunatly I have no idea how to measure the resistance or for that matter any thing else you recomemded:confused: . It is true, when it comes to electronics I am a complete idiot. I have a multi-meter but about all I know how to do with it is see if the alt is charging. Could you give me some details, and I'll give it a try.

 

I'm not sure if it matters, but the guage works the same as it did before the motor came out. Thanks, Tim

 

Using a meter is pretty easy Tim. Before long you will wonder how you got by without it. Is you meter a digital or analog (with a meter movement)? Analog meters usually require a calibration of the meter before testing.

[chef_tim]

It only has a single flat conector. Unless I missed a second wire, but I about posssitive I only saw the one conection. Thanks, Tim

[chef_tim]

Analog, with a needle pointer.

[Cougar]

This is your new '97 model correct? What kind of meter do you have? Refer to my last post.

[Cougar]

Analogs are a little more harder to use on resistance than digital and you need to be sure that there is no voltage to the circuit when you measure resistance. It can damage the meter otherwise. Do you have an instruction manual with the meter? If so, you should read it.

 

Another thing you can do is measure the voltage of the sensor while things warm up. Also it seems to me that if the sensor has only one lead then that would be the one for the gauge and there may be another for the ECU that has two leads to it.

[Cougar]

I need to go get dinner. I will check back in about an hour.

[Olnick]

I need to go get dinner. I will check back in about an hour.

 

So Tim, what are we going to do while Cougar eats dinner?

[chef_tim]

I'm hit'n the rack for the night, I'm about 3-4 hours ahead of Glen . I'll look for the book in the morning, I save everything like that, just a matter of finding it. Again, thanks, Tim

[Cougar]

Your welcome for the help Tim.

 

Learning to use an analog meter is a little more difficult than a digital one but not hard. You need to be more careful when making measurements because the meter movement can be damaged if the scale or the function is set wrong while taking a measurment. All meters need to have power removed from the circuit when measuring resistance. This is because the meter sends out a current to flow through the device under test and measures that current in ohms on the meter face.

 

Most analog meters have a zero adjustment along with a multiplier scale (R x1, R x10, R x1000, R x10,000). The multiplier scale is needed so that when measuring either very low or very large resistances you will be able read them on the scale. If you measure a resistor and the needle moves to 4.5 on the scale you then need to check what multiplier is selected. Let's say it is at R x 100. Then you need to multiply the reading by 100, 100 x 4.5= 4,500 ohms or 4.5k ohms (k stands for kilo or 1000). If the multiplier was set at R x1 then it would be just 4.5 ohms.

 

Before measuring anything though you need to set the zero point on the scale. You do this by set the resistance multiplier you want to use and then short the meter probes together. Then set the needle to read "0" using the zero adjustment. The meter is ready for use then. This is needed for changes in the battery voltage in the meter. Always check the zero when changing scales.

 

To measure current you need to know the polarity of the voltage and place the meter leads in series, with proper polarity, in the circuit you want to measure. You should always start using a large scale so you don't peg the meter and damage it. It is good practice to first remove power to the circuit, place the meter in the circuit you want to measure, then apply power. You need to watch what scale you are set to in order to read the correct current.

 

I guess you know how to read voltages already so I won't mention anything on that unless there is a question.

 

The nice thing about digital meters is you don't have to zero it or watch the polarity. It takes care of things for you and they are usually protected well when the meter is set wrong while checking things. You don't have to worry about what scale you are on also. You should get one when you can. They are not that expensive and really good to have on hand.

 

One thing you can do Tim is disconnect the sensor and see if you temperature gauge changes. I'm pretty sure it will. I think there may be another sensor for the ECU and fans. Have you noticed one?

[chef_tim]

The adventure begins again. I read up on the multi-meter then I tested some "stuff" ie fuses, an exstention cord, a relay. Then I got an old OP sensor with only a single blade conection, I couldn't figure out where to put the meter leads. Going back to the temp sensor, should I put one lead in the conector and the other on the sensor, in effect, making a bridge???

 

Sorry, got an idea and walked away for a sec. My hatch has the same type of conector and it is very accesable. I figured out I don't put it into the power lead, but I put one lead on the sensor and grounded the other one and as the car warmed up, the ohms went down, I ended up with a 4 ohm reading (.4x10). So, with that said I think I'll go check the sensor in the OB, it isn't nearly as accesable:-\ .

 

Really kind of fun learning this stuff:grin: . Tim

[frag]

It only has a single flat conector. Unless I missed a second wire, but I about posssitive I only saw the one conection. Thanks, Tim

 

If I may chime in, what I just quoted seems to point to your engine having two sensors one for the gauge (the single flat connector) and one for the ECU (this second sensors controls the fans and the fuel trim). So you're not looking for another wire but for another sensor (with two wires and probably a brick red connector) just above the one you've already found or very close to it.

Hope that helps.

[Cougar]

I think you will enjoy it even more when you start finding problems using the meter and really understanding the functions.

 

It sounds like you are measuring resistance while the sensor is hooked up and the car is running, if so, remember you need to have power removed from the circuit while measuring resistance. You can measure the voltage though.

 

Does the sensor only have one lead? If so, then you need to use ground as the reference and the meter's common lead (the black, or minus lead) would tie to ground.

[Cougar]

If I may chime in, what I just quoted seems to point to your engine having two sensors one for the gauge (the single flat connector) and one for the ECU (this second sensors controls the fans and the fuel trim). So you're not looking for another wire but for another sensor (with two wires and probably a brick red connector) just above the one you've already found or very close to it.

Hope that helps.

 

You are correct Frag. I've been tring to find out what is going on with that. I thought Tim just got a '97 OBW which I thought had just one sensor with two leads, but he hasn't stated what model this is yet.

[frag]

You are correct Frag. I've been tring to find out what is going on with that. I thought Tim just got a '97 OBW which I thought had just one sensor with two leads, but he hasn't stated what model this is yet.

 

I'm beginning to be a little mixed up with that question of one or two coolant sensors. It is certain that with the appearance of distributorless ignition the coolant switch that was connected to the rad and whose function was to trigger the rad fans dissapeared and was replaced by a dual function coolant temp sensor (fuel trim AND rad fan control).

But it is possible that even on a 97 engine, there is still the coolant temp sender dedicated to the temp gauge. I thought I had not seen any other sensor when I replaced the ECU coolant temp sensor on my 96 2.2L but maybe I did'nt look hard enough.

If Chef Tim's sensor has only one lead, it is certainly a coolant temp SENDER and is not the sensor that is giving him problems.

[chef_tim]

Sorry, 97 OBW build date is Jan 97. I just got off the phone with the service tech and they said there is a second sensor. Black with yellow strip and black wire. It should be toward the front of the engine, but I'm not seeing it. I'm starting to think I may have to take the intake back off and look under it:banghead: . Keep the ideas coming, I'm going back out to look some more. Tim

[Cougar]

I agree Frag.

[frag]

Sorry, 97 OBW build date is Jan 97. I just got off the phone with the service tech and they said there is a second sensor. Black with yellow strip and black wire. It should be toward the front of the engine, but I'm not seeing it. I'm starting to think I may have to take the intake back off and look under it:banghead: . Keep the ideas coming, I'm going back out to look some more. Tim

 

The sensor you're looking for is just under the IAC valve, just under the passenger side rear intake runner and screws horizontaly toward the front of the engine. It usually has a plastic connector of a dark red color. It should not be necessary to remove the intake manifold to get to it but you have to remove the PCV valve vac hose and the IAC air hose and push aside some wire harnesses to get to it with a ratchet extension. It is my experience (on a 2.2L though) that it's very hard to test on the engine (because of placement) and that you have to remove it to test.

You could at least check that it is properly connected. I suspect that this is the problem: this sensor is not connected. Just a hunch.

[chef_tim]

Gentlemen, we have a WINNER!!!!! I would have never seen that as it was. I'm still trying to plug it in (8 stitches across the back of my thumb don't help....lol) So, just for my own knowledge, what does "IAC" stand for, I'm assuming it is the fat hose that goes straight up and down. Thank you, thank you, thank you:D . Tim

 

The sensor you're looking for is just under the IAC valve, just under the passenger side rear intake runner and screws horizontaly toward the front of the engine. It usually has a plastic connector of a dark red color. It should not be necessary to remove the intake manifold to get to it but you have to remove the PCV valve vac hose and the IAC air hose and push aside some wire harnesses to get to it with a ratchet extension. It is my experience (on a 2.2L though) that it's very hard to test on the engine (because of placement) and that you have to remove it to test.

You could at least check that it is properly connected. I suspect that this is the problem: this sensor is not connected. Just a hunch.

[Cougar]

IAC is for Idle Air Control, Tim. So the connector was off as Frag suspected.

[frag]

IAC = Idle Air Control valve.

It's bolted on the passenger side of the throttle body. Easily recognizable by the relatively big air bypass hose that connects to it coming from the main air duct (about an inch in diameter, a little bigger than the PCV valve vac hose).