1990 Chevy Lumina Need Help ASAP PLEASE.

I was told to check the ECm by tap test and also by heat test.

Also to check the ECM relay. Where is it located at?

Hello! I am Mechanicmagg's wife. I wanted to let you know what I did and was wondering if you could tell me what you think about it. I unhooked the coolant temp. Sensor and now both of the fans run constant and the car idles great. I still get a troublecode #15 but I am sure that is because the sensor is unhooked. I have not driven the car for fear that I may damage something but I did let it idle for approx. 30 minutes. It goes into gear great as I have driven it up and down the driveway. Please let me know what you think. Thank you in advance!

What do the terminals look like on the coolant temperature sensor? If any of them have a green tint it is probably corrosion. It can cause a faulty temperature signal. Try cleaning them with a baking soda and water solution about the consistency of heavy cream. Be sure the ignition is off, and coat the sensor terminals with the paste. It will create a chemical cleaning reaction so give it a few minutes to work before rinsing out the connector. Sometimes scrubbing with an old tooth brush helps also. After rinsing dry the terminals and connector thurouglhy. If you have any silicone grease put a light film on the terminals and reconnect the sensor.

I just did that on my wife's car and it solved a persistent, irratic, idle problem. Hope that helps!

Its not a terminal corrison problem because the pigtail and the sensor have been changed. If you unhoon the sensor and use a paperclip to short the wires together in the terminal and the fans run constantly the cars runs OK. When you hook the sensor back up the engine dies.

I am thinking a short in the yellow wire from the ECM to the CTS (Coolant Temp Sensor).

Does anyone have any ideas that make sense.

We really need your help badly.

Thanks.

"Does anyone have any ideas that make sense."

I'm going to choose to assume the last comment was not directed at my previous suggestion. You did not mention replacing the sensor.

"If you unhoon the sensor and use a paperclip to short the wires together in the terminal and the fans run constantly the cars runs OK. When you hook the sensor back up the engine dies.
I am thinking a short in the yellow wire from the ECM to the CTS (Coolant Temp Sensor)."

A "short" means the signal has an alternate path to ground. It should be easy enough test that theory with a mutlimeter or continuity checker.

If, when you short the sensor connector terminals the engine runs properly, it would suggest the output signal to the ECM is OK. I don't know which is the "yellow" wire, but as I recall it is at least a three wire sensor which suggests it requires external power in addition to the output connections. Is there power to the sensor when the ignition is on? Do you have access to a wiring schematic for the sensor? Even "brand-new" sensors have been know to be defective. I'm don't have access to my Lumina manual right now so I can't check myself.

Hello, this is the wife. The CTS has been changed twice. The second time I thought that maybe the first one was bad. All I know for sure is that if I put a paperclip in the wiring, I am able to drive the car. I also know that without the paperclip in and with the fuel pump relay pulled out, that the car also runs fine. But as soon as I plug the CTS back up, the car will not run correctly. By the way the CTS is a 2 wire sensor. I am going to test the wires tomorrow, from beginning to end. Will let you know what I find. Thanks

AutoZone website has free, online, repair manuals. They aren't great, but might be of some help.

see AutoZone 1990 Lumina Ignition Electrical info
https://www.2carpros.com/articles/mitchell1eautorepair-car-repair-manuals

I hope that helps.

I have a Chilton and a Haynes. Thank you anyway.