Temp Gauge instantly goes in the red

[MBruneaux]

Hello All, my son and I just finished replacing the engine on our '01 740iL and bought it non running. Now that it's running we get to find out all the other things wrong with the car . The one problem I can't figure out is the temperature gauge immediately goes full hot when the key is turned to run and the computer reads 298 degrees (checked with a scan tool), I believe this indicates an "Open" ? It's a new temp sensor and tried two other known temp sensors to make sure. I've researched the issue but can't locate the problem, don't want it to be the cluster (IKE?) I've done so far;

1. New sensor and checked with other used sensors
2. Unplugged the battery for 30 minutes
3. Cleaned the terminals
4. Checked for corrosion at the ECM

I am about to dig up the wires from the sensor to the ECM looking for a break.

Thank you in advance

[jpilk99]

Hello All, my son and I just finished replacing the engine on our '01 740iL and bought it non running. Now that it's running we get to find out all the other things wrong with the car . The one problem I can't figure out is the temperature gauge immediately goes full hot when the key is turned to run and the computer reads 298 degrees (checked with a scan tool), I believe this indicates an "Open" ? It's a new temp sensor and tried two other known temp sensors to make sure. I've researched the issue but can't locate the problem, don't want it to be the cluster (IKE?) I've done so far;

1. New sensor and checked with other used sensors
2. Unplugged the battery for 30 minutes
3. Cleaned the terminals
4. Checked for corrosion at the ECM

I am about to dig up the wires from the sensor to the ECM looking for a break.

Thank you in advance

My gut would be either option 4 or likely your closing comment about "dig up the wires from the sensor to the ECM". I've had the Trans Failsafe Error because of a tiny break in the insulation on the wire to the ...thermostat(?). But it was grounding to the block and triggering the error. As you likely know, on these older vehicles, that plastic insulation - after years and years of heating up and cooling down, if you even look at them too hard, the insulation can crack and either break the wire or expose it to grounding.

That would be my guess. Good luck.

Jay

[oldroller]

Here's a shot in the dark... I think I remember a old post about the same circumstance, but I can't find it now.
Seems the owner swapped two connectors, possibly the coolant sensor and thermostat map connection on reassembly
doing tcg's. Swapped them around to correct the issue.

If it wasn't raining like big dogs I'd go check my '01 to see if that is even possible.
Maybe someone with a memory can chime in.

[acspecialists]

The connections on my 00' are different. When I had this problem it was the temp sensor on the water pump. As you did an engine swap I would be checking the wiring.

[MBruneaux]

I plugged in the original temp sensor and the condition was still present. What gets me is, the circuit that feeds the gauge is separate from the circuit that feeds the ECM. So that would mean we have TWO bad wires. The only thing they share is the two way Temp sensor......

[MBruneaux]

It was the &%%@$# sensor.... Replaced the battery, replaced the new sensor with an old one and it worked. Don't know why it didn't work before but it does.

Thank you everyone

[racer2086]

If you tested the sensor not screwed into the water pump, it may not have had a good ground and would have registered as an open circuit. I don't think it can be hanging there... Glad to hear you got it worked out.

[MBruneaux]

If you tested the sensor not screwed into the water pump, it may not have had a good ground and would have registered as an open circuit. I don't think it can be hanging there... Glad to hear you got it worked out.

I believe that is what happened..