1994 Lexus LS 400 Heater not working

Tiny
PREACHDAVE
  • MEMBER
  • 1994 LEXUS LS 400
  • V8
  • 2WD
  • AUTOMATIC
  • 103,524 MILES
We've got a 94 LS400 which the heater stopped blowing any hot air. First thought, thermostat. I've changed it twice---no change. Next, heater valve, or heater core. NOPE clean as a whistle through and through. Tried the valve manually in case it was broke, nothing again. Flushed and filled. Changed all the hoses. Nothing. Relays, fuses, OK, OK, OK. NO CODES SHOWING. Vent motor is working. I have had almost everything out and checked. ZIPPO. I'll take any ideas before I'm completely gray headed. Thanks!
Thursday, November 20th, 2008 AT 9:12 PM

6 Replies

Tiny
BLACKOP555
  • MECHANIC
  • 10,386 POSTS
First thigns first, with a hot engine feel the heater core hoses.

Both hot? One hot one cold? One hot one warm? Both cold? Both hot?
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Friday, November 21st, 2008 AT 5:46 AM
Tiny
RAIDERSAFC
  • MEMBER
  • 1 POST
  • 1994 LEXUS LS 400
  • V8
  • 2WD
  • AUTOMATIC
  • 190,000 MILES
Heater problem
1994 Lexus LS 400 V8 Two Wheel Drive Automatic 190000 miles

We've got a 94 LS400 which the heater stopped blowing any hot air. First thought, thermostat. I've changed it twice---no change. Next, heater valve, NOPE clean as a whistle through and through. Tried the valve manually in case it was broke, nothing again. Flushed and filled. I cut the hose to see if there was any fluid coming out while the enginer was running but there was nothing coming out hte heater core side. Changed all the hoses. Nothing. Relays, fuses, OK, OK, OK. NO CODES SHOWING. Vent motor is working. I have had almost everything out and checked. Nothing. Could the heater core be plugged up? I'll take any ideas. Thanks!
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Monday, February 20th, 2017 AT 6:03 PM (Merged)
Tiny
KAVUE
  • MEMBER
  • 1 POST
Heater Problem- 1994 Lexus LS 400, 204k, car runs excellent, blowing cold air when heat turn on, I thought it might be the fuse but that did not solve the problem. After replacing all the heating fuse it worked for a day then stop. Please help. Live in Minnesota.
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Monday, February 20th, 2017 AT 6:03 PM (Merged)
Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
The engine thermostat may be bad. The heaer uses coolant from the motor so if it is cooler than operating temperature, the heater will make it cold and running the heater even makes it colder.
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Monday, February 20th, 2017 AT 6:03 PM (Merged)
Tiny
  • MEMBER
  • 0 POST
  • 1994 LEXUS LS 400
  • 180,000 MILES
I am getting very little heat in the car. I't will blow out luke warm. Also when on defrost very lttle air comes out of the defrost vents.
My second problem is. I am getting a code 13 I was told I need a new ECU/ECM. Can you tell me where it's located so I can get a used one. And replace it.
I have dune the timing belt and I installed a new water pump and new thermostat at that time. The problem exsisted before the timing belt change.
I have checked the heater contol valve and it is working properly.
I also checked the heater hoses to make sure that both hoses were getting hot to make sure there was no blockage in the heater core.
I cant afford to take it and get it fixed.
My chemothearpy treatments are taking everything from me.
So any help would be apreciated.
Hopefully down the road things will be better. And I can come back to this site and make a donation.
Thank You for Your Time and Help.
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Monday, February 20th, 2017 AT 6:03 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Refer to diagram for Code 13. I don't see it being an ECM problem. Was any testings done?

For the heater system, have you tried checking for trouble codes?
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Monday, February 20th, 2017 AT 6:03 PM (Merged)

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