ynctypes

Hi all,

I am having an issue with my 03 SC430. Starting from two nights ago, the engine temperature gauge has been in HOT position even when the car is cold. It looks like it got stuck in HOT position. What could be the cause(s) of this? Bad temperature sensor? Gauge needle got stuck somehow?

This happened after I forgot to plug a connector back in place. This is a 18-pin connector located under the radio. However, I am not sure how to correlate the two events together, since the wires in the connectors are mostly interconnects from the radio player to the stereo amplifier, and navigation to display monitor. However, there are two wires that go to the combination meter, from navigation ECU and stereo amplifer.

I appreciate any advise. Thank you.

Below is a picture of the connector, from Seattle_Scone

RTIS250

iTrader: (9)

When the ignition is turned off, can you shine a flashlight into the cluster and see if the needle is still stuck on hot? If so, then id blame the needle/guage assy. If it goes to cold, then i would tend to look elsewhere. I would check the sending unit, to make sure the wiring is tight and connected properly. You may have somehow inadvertantly shorted a wire to the cluster. If you can find someone with a Techstream scanner, they can do an active test on the guage and tell you if it is working properly, this would at least eliminate the guage. You can also try to reset the system by simply disconnecting the battery for 15 minutes or so.

ynctypes

Thank you for the information. My car has been parked in garage in the past two days, with the ignition off, the needle is still stuck on hot.

I only worked on the audio signal wires on the connector, R+, R-, L+, and L-. Those wires go from the radio to the stereo amplifer in the trunk.

I am looking at the schematics of the Combination Meter, it looks like the two wires on the connector interconnects the "SPD" on the navigation ECU and stereo amplifer to the combination meter/gauge. Do you know what do those signals do?

Like I mentioned earlier, I forgot to put the connector back in before I started the car. The car wouldn't start with that connector unplugged. The car lost power to everything when I tried to start it, and I had to reset the system by disconnect the battery. After plugged it back in, I could start the car like normal but with this issue on the temperature needle stuck on HOT. Any idea? Does the check engine light come on when temp is on HOT?

I would like to drive over to the dealership but wanted to make sure it is only the problem with the gauge display but not mechanical cooling system before I drive 10 miles.

ynctypes

RTIS250 - I just noticed you are a Lexus Master Tech. I have a question: I disconnected the battery and the needle still stuck on HOT. If I understand the mechanism correctly, the receiver gauge varies its needle position based on the amount of current passes thru it. The resistance of the coolant temperature sender varies with temperature. If I disconnect the battery, there should not be any current flowing thru the gauge, therefore if the receiver gauge is working properly, it should go to COOL. Since this is not the case, I assume it's the problem with the combination meter. Is this a correct assumption?

I wonder how come only the coolant temp gauge has problems but not all the others. The fuel gauge, speedometer, tachometer, and all other LEDs' for engine check, seat belt, gear shift lights, and so on are working properly.

Thank you.

RTIS250

iTrader: (9)

That is rather strange. But if the gauge stays on HOT, even with the battery disconnected, then i would lean towards the gauge being faulty. Start the car and let it run for a while, let the fans cycle, and you should be fine.

the "SPD" wire is the speed signal from the cluster to the navigation ecu. this allows the navigation to work properly, and also turn off certain buttons when you start driving.

It would be a whole lot easier to help if you were local, lol. You can try to pull the cluster out, and see if the needle is stuck.. ive seen needles stick in place, but you can knock them loose.

And yes, when the car hits 255 degrees, the check engine light turns on.

ynctypes

I will give that a shot, the longest I let the car run since this happened was less than 5 minutes. I hope this will solve the problem. Thank you for the advise.

ynctypes

The problem is fixed now. The service guy used a diagnostic tester to force the needle back down and now it's working like normal. I was told that the needle was stuck in place because of either going over a huge pothole (not sure the reasoning) or if there is a power glitch. In my case, it's probably the power glitch that caused it.

I am glad it wasn't the gauge going bad because it's a pretty expensive part.

RTIS250

iTrader: (9)

Glad you got it fixed.. I knew it would be best to run the active test on the gauge to make sure its working or not.