Weird Heating Problem!

paulydude · December 19, 2004

Dudes,

Can you come to my rescue.

My heater works fine in the morning for the first 30 mins or so. Nice and warm blowing out all vents. Then after 30 mins starts blowing cold!! Any ideas. I had a new heater control/clock installed about a year ago so i`m at a loss as what is causing this.

Cheers Dudes

davepruce · December 20, 2004

I have the same problem, if you turn the heater control up 3-4 degrees does yours come back, mine does?

I dont think the new clock/temp would have any effect because they only report what the system is telling them, also had mine replaced and its made no difference

I'm beginning to think that mine maybe the temp sensor wherever that may be, (if anyone knows where it is, can they let me know please) but as I dont do that many long journeys, it doesnt cause me much of a problem

Cheers

Dave.

Rob · December 20, 2004

do u have climate control on that model of LS? if so there will be a small grill somewhere around the dash area - the sensor will be there, as air is drawn in you might find that dust and dirt has accumulated on the temp sensor. that might be the prob????

paulydude · December 20, 2004

Dude,

yeah, if I turn it up a couple of degrees it does come back but not for very long!

I will look for a sensor and let you know how I get on (Fluff).

Does the Temp/clock display have any diagnostic checks that a Simpleton like me can do!!!

Cheers guys :P

ROYT · December 21, 2004

To check the aircon system, turn on the ignition while pressing the AUTO button and the REC [recirculate] button simultaneously.

After the indicator light check the diagnostic code check starts automatically

00 is normal

11 is open circuit or short in the room temp.sensor circuit

12 is same for ambient temp

THERE ARE 11 CODES

Press the OFF button to cancel the test.

To clear the stored code remove the DOME fuse for 10 secs. or more[under bonnet] B)

Silk · December 23, 2004

To check the aircon system, turn on the ignition while pressing the AUTO button and the REC [recirculate] button simultaneously.
After the indicator light check the diagnostic code check starts automatically

00 is normal

11 is open circuit or short in the room temp.sensor circuit

12 is same for ambient temp

THERE ARE 11 CODES

Press the OFF button to cancel the test.

To clear the stored code remove the DOME fuse for 10 secs. or more[under bonnet] B)

←

I am having a similar problem. What are the other 8 codes? I perform the Aircon check above and seem to get codes of 14 and 15.

ROYT · December 23, 2004

Hi!

This is the info from a series 2 ls 400 w/shop manual.

There is no code listed with the number 15

Code 14 is open circuit or short in the water temp.sensor circuit

code 13 open or short in evaporator temp.sensor circuit

code 21 same in the solar sensor circuit*

code 22 same compressor lock sensor circuit*

code 31 same in air mix damper position sensor circuit

code 32 same in air inlet damper position sensor circuit

code 33 open circuit in air mix damper sensor circuit

open or short in air mix servomotor circuit

air mix sevomotor locked

code 34 open in air inlet damper position sensor circuit

open or short in air inlet servomotor circuit

air inlet servomotor locked

*Open circuit in solar sensor and locking of the compressor are detected only when

they are current troubles.Other codes detect both current troble[buzzer sound]and

past trouble[no buzzer sound] ;)

Alex JB · October 24, 2007

Gents,

I was trawling through the posts about heating problems and found this thread.

Has anyone fixed their problem buy sorting the codes?

I have a heater problem where the heaters just about get hot then go cool again unless the car is given some beans and then the heaters get hot again for a while.

I also have a bled out lcd so I'm assuming that's where you can see the codes - so if I di the test I can't see them.

What's the dome fuse look like and where's it located, may pull it out anyway and try to clean the sensors if I can find them.

Thanks,

Alex JB.

Chris Skelton · October 24, 2007

Wow!! All those possibilities....of problems!! Frightening!

Oh for the days of opening or closing a vent!

microcat36 · October 24, 2007

The dome fuse is in the fuse box under the bonnet, behind the Battery, 10 amp.

Alex JB · October 25, 2007

Thanks Microcat

Anyone confirm that the codes are on the heater control screen?

TrevorK · October 12, 2014

I have a problem, if anyone has any ideas. Just bought 2005 LS430. Great Car. The temp control on driver's side of centre console is the problem. If I set it at "cold" then cold air blows from everywhere, but as soon as I change it to 16 deg or above it just blows hot air, with no apparent regulation. The temperature I set it to doesn't seem to matter. It just keeps on blowing hot air until I have to open a window or turn back to "cold"

Anyone else experienced this and any suggestions would be most welcome

Trevor

steve2006 · October 13, 2014

There have been cases where the servo motors have failed and caused these problems or the flaps have jammed or broken off.

The system consists of piping and then various control flaps that control the airflow to different parts of the car as required ( windscreen/feet etc ) and then another flap which controls the warm air/cold air mixing to provide the correct requested temperature.

Not sure how you would go about testing these but perhaps try turning the temperature from cold/hot/cold and listen carefully under the dash for any flap movements.

I would imagine Lexus could also diagnose this with their equipment at a price :(

TrevorK · October 13, 2014

Thanks Steve.

If it is quiet then when changing from cold/hot/cold you can hear a flap (or something) move. Certainly the air warms up instantly and cools down equally quickly..

It just that changing the temperature setting has no effect. I can either have full cold or full hot air.

Will probably take the route through the Lexus engineer and let you know the result

Thanks Again

Trevor

TrevorK · October 20, 2014

Thanks again Steve, and everyone with ideas on this forum.

I used the self diagnosis technique shown on some of these pages and it suggested a fault No 11 (which is either an open or short circuit on the room temperature sensor)

I removed the sensor cover to find a loose connection, which when repaired seems to have solved the problem, at a cost of £0

I am one very happy bunny

So many thanks to everyone on this and the USA forum without whom this would not have possible

Trevor

steve2006 · October 20, 2014

Excellent result :)

goldtop · November 7, 2014

Another heater hiccup here. A Mk4 and the heater has an intermittent issue, where it will sometimes not supply any heating to the air being blown into the cabin. Then, it will come back OK. On some journeys it's fine, others it's not.

In combination with the Front button being used to keep the windscreen demisted, this results in a VERY cold car. :-o

I will try the diagnistic trick above (although I think that's for a Mk3 with a different control layout?)

One other thing to mention (saw it mentioned on another heater thread here): occasionally I hear a water 'sloshing' sound from somewhere in/under the dashboard when accelerating. I had initially thought that this was perhaps rainwater collecting in a void in the bodywork and that I should check it out, but now I wonder if the sound is from the heater unit/pipes and the sloshing sound indicates the presence of air? Which could mean an intermittent air lock stopping the heater from getting a supply of hot water...

cruisermark · November 7, 2014

just an idea - the ls430 has a cabin temperature sensor - have a look if the 400 has one and make sure its clean

http://www.lexusownersclub.co.uk/forum/topic/83025-cleaning-my-cabin-temperature-sensor/

goldtop · November 7, 2014

Thanks - I will take a look (it's doubtless covered in fluff anyway, so worth a clean). Will report back...

ShaksR · March 11, 2018

Just bumping up this old thread as I'm having the same symptoms as goldtop re: cool air being pumped out by the climate control on a Mk4. Did cleaning the cabin temperature sensor under the steering wheel resolve it for you?

JohnDavis · March 12, 2018

On 11/7/2014 at 10:48 AM, goldtop said:

Another heater hiccup here. A Mk4 and the heater has an intermittent issue, where it will sometimes not supply any heating to the air being blown into the cabin. Then, it will come back OK. On some journeys it's fine, others it's not.

In combination with the Front button being used to keep the windscreen demisted, this results in a VERY cold car. :-o

I will try the diagnistic trick above (although I think that's for a Mk3 with a different control layout?)

One other thing to mention (saw it mentioned on another heater thread here): occasionally I hear a water 'sloshing' sound from somewhere in/under the dashboard when accelerating. I had initially thought that this was perhaps rainwater collecting in a void in the bodywork and that I should check it out, but now I wonder if the sound is from the heater unit/pipes and the sloshing sound indicates the presence of air? Which could mean an intermittent air lock stopping the heater from getting a supply of hot water...

The sloshing sound is probably condensed water from the refrigeration, but it should run out of the condensate drains before it ever gets to sloshing volume, so check that the system drains (including rainwater drains) are clear.