Can you ohm the CTS?
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Can you ohm the CTS?
I just went out and disconnected my CTS harness and tried to ohm the CTS. It looks like the FSM says at 70*f, it should read about 3,400 ohms. My harness reads 4.85v. It should work right??
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
I know Bogus, I even double checked and yes it was set on ohms. I tried to ohm the signal side with red lead and a known grond on the frame with black lead. Then I tried to ohm the signal side with red lead and black lead on the ground side of CTS. When I turn the meter to volts the harness reads 4.85v, but got 0 for ohms on the CTS. I guess this is a yes/no type of question with a little insight for more than I know.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
You can ohm out the CTS and you did that correctly it sounds fine. But you can’t ohm out the harness which is really looking back into the PCM (ECM) electronics. The PCM puts out a 5 volt reference signal which you measured. The PCM uses this voltage to interpret the resistance of the CTS and use it for its calculations. 
It is not a good thing to measure resistance back into the harness because the meter on ohms does put out a voltage and you are sending that back into the PCM. Not a good thing to do, you could damage the sensing circuitry.
I would say that it would work right because the resistance of the CTS is OK. You can’t tell anything by measuring the harness voltage other than it is there which sounds OK.
You have to know what a voltage should be for it to be useful data. Other sensors can be measured for useful information (i.e.; MAP & TPS), but not much gain with the CTS.
It is not a good thing to measure resistance back into the harness because the meter on ohms does put out a voltage and you are sending that back into the PCM. Not a good thing to do, you could damage the sensing circuitry.
I would say that it would work right because the resistance of the CTS is OK. You can’t tell anything by measuring the harness voltage other than it is there which sounds OK.
You have to know what a voltage should be for it to be useful data. Other sensors can be measured for useful information (i.e.; MAP & TPS), but not much gain with the CTS.
Melting Slicks
Joined: May 2001
Posts: 3,270
Likes: 26
From: Winchester VA
Cruise-In V Veteran
I don't see where you measured the resistance of the sensor itself. Set meter to ohms and connect leads to each terminal of the sensor itself with harness disconnected. In that case you should get a reading of ohms that correlates to a temperature such as 3400ohms at 70*.
Correct me if I'm wrong, but it seems you tested the harness and output from the PCM but you do not mention actually getting any ohm readings from (across) the sensor itself.
Correct me if I'm wrong, but it seems you tested the harness and output from the PCM but you do not mention actually getting any ohm readings from (across) the sensor itself.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
excuse me, just so I know, how can you get 0 ohms on an ohms test that should read anywhere from 185 ohms all the way up to 100,700 ohms depending on temperature...that's according to the FSM.
6E3-A-27, or 6E3-A-29. I'm lost here, and if his ohm meter was actually reading 0L, he has a problem with an open circuit! Help me here?
6E3-A-27, or 6E3-A-29. I'm lost here, and if his ohm meter was actually reading 0L, he has a problem with an open circuit! Help me here?
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Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
I disconnected the CTS from the connector and did a voltage check of the yellow and black circuit wires. The yellow measured 4.85/ close enough to the 5 the ECM sends with the key on and code key in place. I then turned to ohms and stuck the red lead into the CTS and the ohm meter read 0 even after wiggling the lead around. I had the black lead on a known ground and then on the TPS ground which is the same ground for the CTS and MAT. I never saw an ohm reading with all of this. It was a little difficult sticking the red lead in there with it still on the intake manifold but did good enough I should have got a reading. I did it correctly. When using an ohm meter how do you guys check the ohm reading of the CTS while still in the manifold??
Melting Slicks
Joined: May 2001
Posts: 3,270
Likes: 26
From: Winchester VA
Cruise-In V Veteran
The leads should be touching the the sensor terminals. Not one to a terminal and the other to some other ground. Across the terminals as it it sometimes refered to. And it really doesn't matter which lead is on what side.
Again, meter leads to sensor terminals.
Again, meter leads to sensor terminals.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
I'm going to assume your working on your 95. With your ECT unplugged If you measure from ground to either lead of the ECT it should not measure any ohms or infinity (not 0). There should not be any connection to ground from any terminal of the sensor. The reading is measured across the two terminals of the ECT.
I have to use terminal extenders to make the measurement myself. They are to recessed and I can't see them. If you are really measuring the sensor on the water pump and the reading is 0 ohms to ground, then the sensor could be shorted to ground. If you are measuring correctly.
I would get a known value resistor say 1000 ohms and measure it just to make sure the meter is working OK.
I have to use terminal extenders to make the measurement myself. They are to recessed and I can't see them. If you are really measuring the sensor on the water pump and the reading is 0 ohms to ground, then the sensor could be shorted to ground. If you are measuring correctly.
I would get a known value resistor say 1000 ohms and measure it just to make sure the meter is working OK.
Last edited by pcolt94; May 24, 2006 at 06:38 AM.
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Originally Posted by RainDelay
The leads should be touching the the sensor terminals. Not one to a terminal and the other to some other ground. Across the terminals as it it sometimes refered to. And it really doesn't matter which lead is on what side.
Again, meter leads to sensor terminals.
Again, meter leads to sensor terminals.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Just some suggestions;
1) Make sure the meter is working right.
2) Make sure you are on a scale that will allow you to measure the resistance value you expect to see (if you don't have auto ranging).
3) Are you sure you are making contact with both terminals of the CTS.
If all is good then you might have a bad (open) CTS.
1) Make sure the meter is working right.
2) Make sure you are on a scale that will allow you to measure the resistance value you expect to see (if you don't have auto ranging).
3) Are you sure you are making contact with both terminals of the CTS.
If all is good then you might have a bad (open) CTS.
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Originally Posted by pcolt94
Just some suggestions;
1) Make sure the meter is working right.
2) Make sure you are on a scale that will allow you to measure the resistance value you expect to see (if you don't have auto ranging).
3) Are you sure you are making contact with both terminals of the CTS.
If all is good then you might have a bad (open) CTS.
1) Make sure the meter is working right.
2) Make sure you are on a scale that will allow you to measure the resistance value you expect to see (if you don't have auto ranging).
3) Are you sure you are making contact with both terminals of the CTS.
If all is good then you might have a bad (open) CTS.
2) I tried it in 20, 200, 2,000
3) I wiggled both leads around in there for about 30 sec
Sounds like a bad sensor if this is the case.
I will give it one more try this afternoon.
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Alright, I removed some of the crap in front of the sensor and used the ohm meter again. It reads 2,200 ohms and the ouside temp here is about 80-85*. I think it should read higher than that what do you guys think?
Thread Starter
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Sorry guys, It is reading correctly. At 70*f it should read 3,400 ohms and at 100*f it should read 1,800 ohms. It is about 85 here and it reads 2,000 ohms, just right. Well troublshooting paid off this time guess I'll save that $12. Thanks for everybody help on this one. Looks like case closed.
