i posted this in the electronics forum realizing that may have been the wrong section...i am open to almost any suggestions, the car is in a heated garage downstairs so i can try whatever i'm told as soon as i'm given something to do. Basically the run down...i got a code 15 since i got the car 6 or so months ago - tryed different ECU (suggestion of a fellow member, it happens to be remanufactured by delco so it's not 20yrs old like mine was): still got it. as far as the harness for that car, there is absolutely NO corrosion on the harness for that ECU as thats how i took it out, by cutting the harness and computer out. - disconnected ECU and put 12V at the yellow wire and the black wire (seperately), and tested the other side (CTS harness plug) and got exact voltage of source, no drop what so ever - checked for corrosion at the CTS harness plug and ECU (after reading that that is a problem for some), there is NONE - dash temp switch in driver side head works the guage - fan switch in the passenger side head does not work people are running auxilary fan switches which i'm assuming they are just grounding the fan switch wire anyways, so i'm not assuming that is the fault, but the switch is rusted solid and i'm having difficulties getting it out so i can't change that right off the bat although i do have a replacement. i haven't figured out how to use my digital volt meter to test ohms properly, as i continue to get a 10.00 with a blinking 1 reguardless of if i'm touching something to not. So i can't tell you the resistance of the wires, but as i said i put a 12.19 V source on one side and got exactly 12.19 on the other side of the wires. As far as the car...with the ECU reset, the car starts, and at normal cold, it will idle high for like 5 minutes, then at 5 minutes, something clicks over, kicks the code, and then sputters for a second, then idles at ~700 RPMs, of which i need to kick on the a/c to activate the fan so i think it spikes to ~800 RPMs, nothing serious...just at 5 minutes it clicks over and goes down significantly (closed loop??). Anyways, if in the first 10-15 minutes of idling i step on the gas, it has the fuel injection quick responsive throttle. After 20 minutes or so of idleing, it acts almost like a poorly tuned carbeurator and i step on the gas quickly and it's like i'm closeing all the air off from the engine and it wants to choke/die, but will fight it's hardest to stay alive (to the point of maybe 50-150 RPMs), and eventually come back to steady idle...just a couple more details that might prove useful.

Code 15 is for CTS low. This is basically an open circuit failure. It can be caused by: bad ECM harness ground (back of pass head), bad CTS, bad CTS connector, open wire, or open or intermittent connection at the ECM (harness pin).

Some stuff you can try: remove connector from CTS, key-on, engine-off, measure the voltage from each pin to the engine block (ground). The yellow should be at 5V, the black should be at 0 volts.

Check the pins at the ECM. You may need to pop them out of the connector and re-tension them.

RBob.

thank you for your responce!

as mentioned, tried a second ECU with the same results (i understand if it's the harness plug that would still do that)

just tested the leads with the ignition in the "ON' position: 5.08V at the yellow wire, 36 mV on the black wire...what does that mean!? if i hold the lead on the black wire it will slowly (.1 mV per second) count down. This was grounded out on the bolt to the thermostat housing. Does this rule out the ECM harness ground mentioned in your post or are there multiple grounds to the engine?

How would you describe re-tensioning the pins?

Also how can i properly test the CTS ohm resistance? I'm heating the garage to 70*, which from the research i've uncovered is the start of the temperature/resistance chart that i found. As i said i put the positive terminal of the digital volt meter on one terminal of the sensor and the black on the other terminal and i get 10.00, with a blinking one (reguardless of if i'm touching it or not). So i think i'm doing that wrong, if you could steer me in the right direction i would like to rule out a dud CTS (as it was new off the shelf).

Thanks!!!

The CTS is a variable resistor. At room temperature it is about 3.2K ohms. Can measure this with the ohms scale on the DVM.

RBob.

The DVM that I'm using, you put it on ohms, and you get 10.00 with the 1 blinking. This is regardless of touching the sensor or not. I believe I may have to find another DVM unless I'm doing something wrong.
Thanks

Ok, physical temperature of garage is 66.5*F

Set the 2nd DVM to "20K Ohms" and got a result of 5.05 ohms, went back to my original DVM (of which decided to work finally), put the setting to ohms, and got 5.05K Ohms.

From the charts that i have found and above information...between 67*F to 70*F should be around 3100-3200 ohms. Why am i getting 5050??? I understand atmosphere temp and phsyical temp of the block may be different, if it was another 10* or so colder on the block of the engine, would it spike 2000 ohms? What is a bonafide way of testing temperature/ohm rating without an infared temperature gun?

Going to tinker with the ECU harness pins now to see if i can re-adjust them, as mentioned i get 5V from yellow and the black is connected to 3 other sensors...i don't see if it was that wire why i wouldn't get more codes but i will go check that now...open to all suggestions!!! Thanks!

Most likely you just have a bad coolant temp sensor. If you the best way to check is with a scanner and see if the temp sensor reads the same as the actual coolant temp(measured with a therometer in the coolant). If the scanner shows a temp of -45 definatly a bad sensor. Running the engine with the scanner and thermometer and comparing the readings will show any problems, both should be within a couple degrees, if not -bad ECT sensor.

ok question...ECT sensor and CTS is the same right...? just double checking. I have a scanner, but i have a feeling is strictly codes even though i swear when i bought the damn thing is said that it did live journalling of engine stats.

Anyways, figured i'd remove the seonsor and hold it in my hand with a thermometer to heat it up. Got the thermometer up to 92*F and took a resistance test. Yeilded 2100ohms, which according to the chart i have is right on the scale so i'm going to think that the sensor works. I was running the engine at the time with the radiator flush mix/water, so i'm going to drain the system and put radiator fluid in there and go from there. I took out the CTS and there was no fluid in there, so i'm praying that the water evaporated or went somewhere, since i did an intake swap i'm worried that it's leaking gaskets so i'm going to change the oil in the same turn to make sure it's not going into the engine. Hopefully the water just evaporated somehow. I will get back to you once i change the fluids.

when testing the CTS...should i have instant Ohm readings when touching each terminal? or do you have to move your readers around a bit. I have to try touching it a couple times to get it to work...and it's happening on both digital volt meters...i don't have the original CTS to test for similarities.

HI, I have an 89 camaro with a v6 and got the same problems you had. When I turned the ac on the engine idled down to low 500-700 rpm and turned off a couple of times. After 3 months of storage. The car would not start at all. I got a reader and got a code 15. Change the colant sensor and now I get code 12. Car still will not start. Seems like it is not getting fuel. I don't have alot of fancy tools. Any help would be appreciated.

Code 12 is the "handshake" code. That's normal.