Help! no heat.
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Driver School Candidate
Joined: Jan 2014
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From: nc
Help! no heat.
Hello, I have searched this topic to no avail. I have a 91 ls400 which sometimes overcharges the battery to 19 volts. haven't solved that problem yet, but now I have no heat. I have checked all fuses and none are blown. when I say no heat I mean I have no power to climate control.
Lexus Champion
Joined: Dec 2011
Posts: 4,078
Likes: 87
From: Birmingham, AL
It sounds like the two issues that may well be related
first, you MUST correct the over-voltage issue immediately - this is normally due to the voltage regulator circuit which is within the alternator - you can either swap out this portion of the alternator or else replace the alternator, but either way, you are going to ruin many circuits in your LS400 if you don't fix this now.
Once the 19 volt issue is fixed and your charging voltage is below 15V at the battery, then we can solve the heat issue, if the alternator repair or replacement doesn't immediately solve it!
also, the most common cause of alternator failure in the LS400 is power steering fluid leaking on to it, so if you have a power steering fluid leak, you need to fix that as well, or else the new alternator will quickly die
first, you MUST correct the over-voltage issue immediately - this is normally due to the voltage regulator circuit which is within the alternator - you can either swap out this portion of the alternator or else replace the alternator, but either way, you are going to ruin many circuits in your LS400 if you don't fix this now.
Once the 19 volt issue is fixed and your charging voltage is below 15V at the battery, then we can solve the heat issue, if the alternator repair or replacement doesn't immediately solve it!
also, the most common cause of alternator failure in the LS400 is power steering fluid leaking on to it, so if you have a power steering fluid leak, you need to fix that as well, or else the new alternator will quickly die
Thread Starter
Driver School Candidate
Joined: Jan 2014
Posts: 3
Likes: 0
From: nc
It sounds like the two issues that may well be related
first, you MUST correct the over-voltage issue immediately - this is normally due to the voltage regulator circuit which is within the alternator - you can either swap out this portion of the alternator or else replace the alternator, but either way, you are going to ruin many circuits in your LS400 if you don't fix this now.
Once the 19 volt issue is fixed and your charging voltage is below 15V at the battery, then we can solve the heat issue, if the alternator repair or replacement doesn't immediately solve it!
also, the most common cause of alternator failure in the LS400 is power steering fluid leaking on to it, so if you have a power steering fluid leak, you need to fix that as well, or else the new alternator will quickly die
first, you MUST correct the over-voltage issue immediately - this is normally due to the voltage regulator circuit which is within the alternator - you can either swap out this portion of the alternator or else replace the alternator, but either way, you are going to ruin many circuits in your LS400 if you don't fix this now.
Once the 19 volt issue is fixed and your charging voltage is below 15V at the battery, then we can solve the heat issue, if the alternator repair or replacement doesn't immediately solve it!
also, the most common cause of alternator failure in the LS400 is power steering fluid leaking on to it, so if you have a power steering fluid leak, you need to fix that as well, or else the new alternator will quickly die
Thread Starter
Driver School Candidate
Joined: Jan 2014
Posts: 3
Likes: 0
From: nc
Thanks lscowboyls! The overcharging has been plaguing me for months. Had the alternator repaired but same problem occurred. Went out today and checked the heater relay, plugged it back in and it worked! Also no more overcharging. Do you think failing caps could cause the overcharging? I have read your thread on that but I am not experiencing any of those symptoms. I have also inspected it very well and see no signs of leaking.
Lexus Champion
Joined: Dec 2011
Posts: 4,078
Likes: 87
From: Birmingham, AL
91 LS400 capacitors are not the problematic ones of 92-97, however, they are 23 years old 
, so while they may not be causing any major issues, replacing them with the ones I have specified in post #1 may very well result in even nicer shifting and more low-end power as so many people are reporting, due to the fact that these capacitors were meant to last around 12 years or so before their capacitance begins to degrade.
, so while they may not be causing any major issues, replacing them with the ones I have specified in post #1 may very well result in even nicer shifting and more low-end power as so many people are reporting, due to the fact that these capacitors were meant to last around 12 years or so before their capacitance begins to degrade.
Lexus Test Driver
Joined: Jan 2012
Posts: 832
Likes: 8
From: CA
I think that if the battery is receiving 19V at the terminals, two things will happen:
1. It will produce hydrogen at a pretty amazing rate, and will quickly deplete the electrolyte.
2. It will then permanently sulphate the plates.
LScowboyLS is spot on regarding the voltage regulator.
I am amazed that the battery will hold a charge at all (unless you are adding distilled water to it constantly).
IMHO, you need or soon will need a new battery.
LScowboyLS, what do you think?
1. It will produce hydrogen at a pretty amazing rate, and will quickly deplete the electrolyte.
2. It will then permanently sulphate the plates.
LScowboyLS is spot on regarding the voltage regulator.
I am amazed that the battery will hold a charge at all (unless you are adding distilled water to it constantly).
IMHO, you need or soon will need a new battery.
LScowboyLS, what do you think?
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