winter4w

Hello everyone,
I got a new issue I just noticed with my car. I got a 1996 Lexus LS400. My fan speed will randomly change to full speed for a second or two and then resume back to the normal setting set. The weird thing is the fan speed indicator does not change at all. When I turn off auto and set the fan speed to the lowest possible setting it will still randomly speed up to full blast then go back to the setting. Does anyone have any idea as to what's going on here?

Thanks

winter4w

Just did a Climate Control Diagnostics and the code I got is 00 which I assume means no errors? Seems like at random it gets stuck at full fan speed. Does anyone have any suggestions?

Thanks

Losiracer2

I think your ECU caps are failing, has the ECU been rebuilt?

YODAONE

Your cabin filter is not clogged?

Unsure if this would have any bearing, but if 96 climate control is similar to 99, then three temperature sensors.. one in each duct behind each front side vent,.and another in the dash undercover immediately below steering wheel near center console.

See:

https://www.clublexus.com/forums/ls-...000-ls400.html

I have a spare 96 control control head and amplifier.

The 7-segment LCD Display is black (LCD display component is available) but the amplifier board could be used to see if yours is tired. PM should you require help.

winter4w

It has not been rebuilt as far as I'm aware. Don't ECU failures have other issues show up too?

My filter is clean, if it was the temperature sensor failing wouldn't the climate control show the fan at max speed? Even when I set it to low speed and turn off auto it will still blow at the high speed.

YODAONE

My 1999 system is a little bit quirky.
Have replaced capacitors on my climate control amplifier and the under dash sensor. Mine was caked with dust.
Had a random code 42 that, but it coincided with clogged cabin filter(?)...mine clogs quickly.

Voltage Drop?

Your negative battery cable and grounds are in good condition?

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/828619-negative-grounding-issues-2.html

Running on original 32 year old fuses?

Replaced all fuses and fusible links (use only Toyota fusible links).

https://www.clublexus.com/forums/ls-...400-fuses.html

https://www.clublexus.com/forums/ls-...se-to-use.html

winter4w

Voltage seems normals, I do have a dash cam plugged in that monitors that and all looks good. I do still have the original fuses in there possible that can be the issue?

winter4w

Okay so here is a video I got of it acting up. It's hard to hear me in the video but as you can see I change the fan speed settings and the fan speed remains at full speed. I also played around with some of the other settings and as you can see it has no effect on the fan speed.


Looking around online I found this post here (https://us.lexusownersclub.com/forum...motor-problem/). This guy seems to have the same issue as me except his fan speed is going to the low setting where mine is going to the high setting.

I also came across this post (https://us.lexusownersclub.com/forum...ystery-solved/) which shows it could be a Blower Motor Controller / Resistor. Do you guys think this could be the issue? If so is this the correct part number for the part? #8716550010

Thanks

Yamae

Yes, the part # is 87165-50010.

Before replacing it, I would check the waveform of the drive signal at the pin #1 of the controller 's 3 pin connector below to confirm that the problem is caused by the HVAC computer or the controller. It's a PWM signal. Does the duty ratio change in accordance with the setting speed? If so, the HVAC computer seems to be OK and the FET in the controller is half dead. A simple voltage meter can be used to check the duty ratio reading the average voltage though.

I sometimes find these type of controllers have a partially dead FET inside. In order to fix it, I simply replace the FET using an equivalent one.

Yamae

This is for a Celsior but I think this might help you to find the location of the controller.

YODAONE

Have a spare controller and acquired several images of internal components.

Image of controller from 1999 LS400.


Cover removed. There are 4 capacitors. Values are on opposite side, but it appears complex formed capacitor leads are flattened where joining the buss bar structure as if they are fused/welded vs. soldered (??) Anyone know? Yamae?.

Yamae

Out of topic. Do not override the thread.
We are discussing about a 96 here. A unit for a 99 is newly designed to reduce both the size and dissipating heat. Those two are totally different. Why don't you start a new thread about a 99.

YODAONE

So, the only unit immediately at my disposal is from a 1999.
Four electrolytic capacitors reminds me of a ceiling fan speed control.

So back on topic, is the 96 unit repairable or is replacement the only option?

Perhaps someone with a 96 unit is willing to open and share circuit images.

Yamae

The replacement is the only way for most of people but some skilled people can repair it analyzing the circuit and find out the exact failed part. As far as I have experienced repairing different failed controllers for JDM cars and imported cars, majority of failed parts were the switching FETs and surge protection diodes. There were soldering cracks too. A controller handles a big current peaking sometimes more than 30A and the stress caused by the heat cycles damages soldering points. Smart engineers will choose the welding method to those high-current points. I seldom find Nissan's controllers welded like yours. Sometimes I find the problem is caused by the failing motor too, I must add.