fritzvis

Hi,

Just introduced myself in the proper section of this forum. I recently bought a 1989 Cadillac Brougham that has an Oldsmobile 307 engine. I have a check engine warning and pulled code that engine temperature sensor is faulty. When I look at front top of the intake manifold I see 2 different sensors. on the left side there is a sensor with only 1 green wire leaving the sensor. On the right side (right next to the other sensor) there is another sensor with 2 wires leaving the sensor, a yellow and black wire.
I need to change the sensor that controls the engine management...
I also noticed that when I start the car, the cooling fan is immediately on, even with a cold engine... it is not an electric fan, but the original fan that was on the car...
all the help is appreciated because I have no experience with those fine V8 engines, all we have here are those boring 4 cilinder diesel engines

oldcutlass

The sensor is the one with the green wire. The fan will always spin with the engine, the mechanical clutch it is attached to will vary in strength depending on temperature.

fritzvis

Hi Eric,

thank you for the info. So the sensor with the green wire is connected to the management system and communicates with carb and transmission. The other sensor with the yellow and black wire is just there for the red light on the dash that warns for high coolant temperature.
The sensor with the green wire has only 1 connection. How can this sensor be tested. I tried to test it with an Ohm meter, but the red wire of the tester on the connector and the black wire on the brass casing of the sensor but I end up with a solid 1 on the meter. Is that the correct way to test the sensor, or is there another way?

rob1960

fritz,I believe the sensor with the green wire is for the temp light on the dash not the engine mgmt system. Gm used a green wire for the temp lamp(or gauge) for years. If you touch the green wire to ground quickly with the ignition on the temp lamp should light up. The websites like rockauto etc, show the computer temp sensor having the 2 wires.

oldcutlass

Sorry that's what I meant the green wire is the temp sensor and the 2 wire is the management sensor. Rob is correct, if you have a temp light, that sensor is either on or off.

fritzvis

Hi and how can i test if the sensor with green wire is good or faulty? Since there is only 1 wire connector I used an Ohm meter and put red wire on the sensor connector (where normally the green wire is) and the black wire on the brass casing of the sensor. i got a 1 reading on the meter. When i put sensor in boiling water, it still reads 1... Or is there another way?

oldcutlass

The single wire sensor probably won't close until the temp is greater than 260F. Boiling water is 210F. Like Rob stated, touch the green wire to the engine and the light should come on.

fritzvis

You are correct Eric, when I ground the wire the red light on dash lights up thanks for the very useful info best regards,
Fred

fritzvis

Just installed a new sensor and boy what a difference in throttle and gear change response like driving a completely different car i had 2 check engine codes : coolant temp sensor and tps sensor fault and replacing the coolant temp sensor solved both the trouble codes oh, and I tested the old sensor and yes it was fried

oldcutlass

Glad you got it fixed.

Octania

details on how you tested the fried sensor would benefit others who read this in the future.

Ohms meter, what reading is good, what is bad, stuff like that.

fritzvis

Your help is very much appreciated Eric, posted my problem also in another forum without a clear answer your post made the difference best regards

fritzvis

Hi Octania, testing the faulty sensor with my Ohm meter just gave me a solid 1 reading on the meter... Means that there is no more current flow between the 2 contacts. When set on 20000 Ohms my good sensor gave 5800 Ohms in cold and when putting it in warm water water it should go down... Very easy to check. but when it says 1 to start with, you know it's lost

Octania

so, instead of "some" ohms, it showed infinite or open circuit?

fritzvis

Yes. There are a few things to take care of when testing your sensor. The easiest way is to take it out of the engine. When doing that coolant fluid will run out of the system. I play the bagpipes and have rubber plugs to block the drones of my pipes. I use such rubber plug to close the hole from the removed sensor. That is very easy. If you don't have a plug you could drain the system partially but that is more work just to change or test a sensor. Watch out what you use to plug the hole, that it does not leave parts in you cooling system. Plugs like cork can break and if there are particles that are left inside the engine could mean trouble

Start with testing if there Is 5V of current reaching the sensor. Use a Volt meter, ground the black wire of the sensor and with red wire touch the yellow wire of the harness that goes into the sensor. If there is no 5V, check fuse in fusebox or check harness plug or search for a cracked wire.
Then check continuity with you multimeter. Again ground black wire of the multimeter and touch black wire of the harness plug... If there is no audible signal from the multimeter then again start searching for a problem with the black wire coming from the harness plug... If all that is ok, test the sensor with the Ohm tester on the multimeter. There a 2 contacts on top of the sensor. Touch one contact with the black wire and the other contact with the red wire from the multimeter. Heat up a bowl of water. Put the sensor with only the tip in the water that is heating up. You should see a reading that is going doing while the water is heating up. Take the sensor out and again put it with tip in cold water, you will see the reading on the meter increasing. That is a good sensor! If you have no reading to start with (reading 1 on the Ohmmeter) then the sensor is faulty. I put a lot of teflon tape on the treat of the sensor when installing is back in the engine to be sure it is not leaking. Make sure you top up your cooling level afterwards or testing your sensor could be a costly mistake

oldcutlass

The Teflon tape can act as an insulator with these sensors. I would use a light coating of liquid thread sealant. Pipe thread is tapered to allow for the joint to seal as you tighten it.