Hey guys, in an effort to find out why my car doesn't run right/idle while cold, i checked the resistance on the coolant temperature sensor.

Key-on, when cold: 635 ohms
no key on, cold: 1350 ohms

And the weird thing is, the resistance rises as the temperature rises. I read the FSM, and the resistance is suppose to fall as the temperature rises. The temperature outside is about 40 degrees. Can the sensor actually go bad and make the resistance start low and rise? Or is this an ecu problem?

http://img.photobucket.com/albums/v465/djgeorge2k/fsm1.jpg

Also, i put a 150 ohm resistor in the coolant temp sensor plug to see if the fans would come on, and they don't. My fans do not come on at all. I bled the coolant system of air, also.

You need to unplug it when you test it Dave. You can't measure resistance when there's voltage going through it.

C

Yeah I have often wondered if this would cause an idle problem as well my U12 motor is running with a U13 ECU and GTI-R MAF, When I checked resistance on the temp sensor I got nothing out of it... Maybe I am doing it wrong? Anyone know how to check resistance so I can make sure I am doing it right? Also not to thread jack but does anyone know if the U12 temp sensors are the same as the U13? If not which one should I use....... B14?

If it's a single contact sensor, just unplug it, and test from the contact to ground. If it's a 2 contact sensor, then uplug it and probe both contacts. Polarity doesn't matter since it's just a resistor.

C

You need to unplug it when you test it Dave. You can't measure resistance when there's voltage going through it.

C

Ok, i went out and did that. I got 1230 ohms at the sensor, with it unplugged. I did run the motor for a bit, so i'll test it in an hour again. Going by the chart, at this temperature today, it should really read 4K ohms , around there.

Remember, it's reading the temp of your coolant, not the air. As a matter of fact, I don't even know if it's going to be immersed in coolant with the car off.

If you can keep the car running with the sensor unplugged, and your DVM hooked up, you should see the resistance value change as the car warms up.

Or just remove the damn thing and run some hot water over it in your sink, or drop it in a pan of hot water. And if you're a real Mr. Wizard, drop a thermometer in the water so you can see if the sensor's accurate.

C

I just noticed that the FSM shows Voltage vs. Temp also. In that case, you can plug it back in and test for voltage instead of resistance.

C

Remember, it's reading the temp of your coolant, not the air. As a matter of fact, I don't even know if it's going to be immersed in coolant with the car off.

If you can keep the car running with the sensor unplugged, and your DVM hooked up, you should see the resistance value change as the car warms up.

Or just remove the damn thing and run some hot water over it in your sink, or drop it in a pan of hot water. And if you're a real Mr. Wizard, drop a thermometer in the water so you can see if the sensor's accurate.

C

Maybe i'll be a Mr. Wizard.

Well, i just checked it again and it IS going up, so that makes sense right now (checked it and it was at 1325).

I can't keep the car on unless i rev to 3,000 rpm's while it's cold, whether or not the sensor is plugged in or not. When it isn't plugged in, the car will hardly start.

Ok, just checked it again...it's just shy of 2k ohms. I now believe that my ecu is to blame. When i discconect the sensor plug, the fans do not come on. When i put a 150 ohm resistor on the sensor plug, the fans do not come on (they should, as the FSM says they should). I jumped the circuit at the relay box, and the fans come on. It's not a wiring issue.

yeah sounds like an ecu or a relay

Ok so i tried a known good ecu and the car does the same thing. I'm stumped. There's not much left to check as far as the fan issue is concerned. I start the car and if i don't give it any gas, it shoots to 1200 rpm's for a second, then shoots down and dies. Bad throttle response under 2,000 rpm's, fans don't turn on unless i jump them at the relay box.

Dave, when you've replaced this many parts and still have this many problems I'm gonna say you should go over all the grounds in the system.

C

Dave, when you've replaced this many parts and still have this many problems I'm gonna say you should go over all the grounds in the system.

C

Ok, here's the deal. I tested the coolant temp sensor circuit again. I went over the whole fan circuit a billion times. I tested the voltage on a cold motor on the coolant temp sensor circuit: 3.3v (equivalent to about 55 or 60 degrees)
With a 150ohm resistor: .45v (equivalent to well over 200 degrees, aka which would turn the fans on)

At the relay, there is a coil part and a switch part. At the switch part, i get 12v, which is fine. Now the weird thing, i get a constant .67v at the coil side of the relay, whether or not it's reading 3.3v or .45v from the coolant temp sensor circuit. To set off that relay, it needs alot more than .6v. We tested the relay at the battery and it clicks. Now i don't know how much it needs, but i'm guessing 8 or 10v. So maybe i have a bad ground, i don't know. Any ideas why the ecu won't click the relay on? This is the second ecu i've tried, so that can't be it!

Some good info here Dave.
http://www.autoshop101.com/forms/hweb2.pdf

How about you list the voltage at each pin number for us.

C

I went through the whole self check in the FSM to test for the relay circuit.

Everything checks out fine. LOL and now i tried jump starting the car and it won't start. I am really getting frustrated. The car started this morning and now it won't turn over.

Relay #1 = 12V
Relay #3 = 12V
Relay #2 = 1.65V (before it read .6, now it reads 1.6, i don't know why)
Relay #5 = 0v (this goes to the cooling fans, when i connect this to 3, fans kick on)


Chris, i know how a relay works...........

OK! Well, i made some great progress tonight. For some reason, the fans now kick on with the CTS unplugged! Great news. So now i basically know that the sensor s bad and not the ecu. Very good news. I'm gonna order a new sensor and get it in there.

Funny.. ive had my car down for about a week now.. was runnign right before.. Now i have the same issue.. when its cold car starts right up and stalls unless I hold it for a few... I kept thinkin i had a big vacuum leak, but I think I have come down to this conclusion as well.

Did you figure out why the car wouldnt start?

Did you figure out why the car wouldnt start?

Well i added a ground from the IM to the block and the car started right up with a jump.....so i don't know if that was the problem or the car was just acting like a pussy last night :tongue:

dave what color ects are u using?blue?