1996 Es 300...obdii Giving P0115 Code...

[1991LS400]

Overheating problem.

This morning while driving for 30 min, with the A/C on, I noticed that at one point in my trip I was idling in traffic for a while when I noticed my temp gauge going up to red drastically. Then the engine started smoking from the coolant reservoir side. I opened the hood to find the coolant ABOVE the full line and bubbling hot. It was so hot, the rubber cap had popped off and coolant was bubbling out of the coolant reservoir (overflow tank).

Immediately afterwards, a check engine light came on. I read it with the OBDII and it stated the following:

P0115

Engine Coolant Temp

Circuit Malfunction

Is this a CTS (coolant temperature sensor) problem? The radiator has been changed and has no leaks so that's not the culprit. I was thinking it was either a bad water pump and/or thermostat but I didn't notice any coolant coming out of that area this morning, however, I do want to change the water pump and thermostat soon. But for right now, I need to find out a quick fix to this overheating problem.

The engine only overheats when the A/C is on too. I also noticed the fan wasn't spinning as fast as I think it should be.

So should I change the sensor first to see if it fixes the problem? Also, does the 1996 ES 300 have a coolant temperature sensor and a coolant temperature circuit or is it both the same thing? Because each auto store I've gone to to try and find a CTS it isn't the right one and is significantly smaller than the one I pulled off that was located by one of the radiator hoses on the right side of the engine (standing in front of it).

Somebody knowledgeable in this area, please help. Much thanks in advance.

[1991LS400]

UPDATE:

- changed both the coolant temperature sensor and the coolant temperature switch

- no coolant leakage from the water pump/thermostat area

- ONLY starts overheating when car is idle with A/C on for 5 minutes or more, does NOT overheat while car is driving (even with A/C on or off)

diagnosis? hydraulic fan problem?

[CUMan]

I went through the same problem early last year.

Read this thread:

http://us.lexusownersclub.com/forums/index...mp;#entry200503

Your problem likely involves the operation of the hydraulic cooling fan.

[1991LS400]

I went through the same problem early last year.

Read this thread:

http://us.lexusownersclub.com/forums/index...mp;#entry200503

Your problem likely involves the operation of the hydraulic cooling fan.

but the mechanic here at the shop said he would change the hydraulic motor on the fan because that's "most likely" the problem. he said nothing about that solenoid on the power steering pump. how would I know if the hydraulic pump on the fan is bad or if it's the solenoid by the power steering pump?

I also noticed a skinny wiring harness that has a small white plastic clip unconnected near the back of the engine, passenger side, right by the firewall that was disconnected. I couldn't see where it would have originally been connected to. I have no idea if that unconnected wiring has anything to do with the overheating (if, as you say, it's not the actual hydraulic motor on the radiator fan).

[CUMan]

My guess would be that the disconnected wiring harness you saw is the source of your problem.

There is a fan control ECM somewhere under the glove box inside the car. This receives a signal indicating how hot the engine coolant is. When the coolant reaches some certain temperature level, this control sends a signal to the power steering pump to increase fluid flow. This, in turn, causes the cooling fan to speed up.

There is a solenoid on the power steering pump. The harness you saw should plug into this solenoid. When this connection is made, and the coolant gets hot, you should see a noticeable increase in the fan speed.

I think that this problem occurs because the cooling fan operation for some Toyota and Lexus models in the early to mid-90's is so unusual. Folks working on the engine do not realize the importance of this particular connector. My problems occurred after I had the valve cover gaskets replaced. In doing this, somehow the mechanic damaged the connector. He plugged it back in to the solenoid, but the damage he had done caused it to not give the proper signal to the solenoid.

[SKperformance]

On your 1mz fe the power steering pump double as the hydraulic fan pump. It is located at the back of the engine on the passenger side almost against the firewall , Sounds like you know what to do know . Plug it back it and it should activate the solenoid again.

[1991LS400]

On your 1mz fe the power steering pump double as the hydraulic fan pump. It is located at the back of the engine on the passenger side almost against the firewall , Sounds like you know what to do know . Plug it back it and it should activate the solenoid again.

SKperformance and CUMan, thank you both for all of your help! unfortunately, I figured it out myself this morning before reading both of your guys' posts but yes, you guys were right, that skinny wire with the white plastic clip was the source of the problem and was the reason why the fan wouldn't turn faster when the A/C was on and the car was idling. too bad I wasted $130 on the coolant temp sensor and the coolant temp switch. Oh well, I already replaced those two things, anyways, the old ones looked like they were going to crack in half anyway. so I guess those two things are out of the way now.