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Lexus LS: Problems & Solutions



  • pj2323pj2323 Posts: 43
    paul: i checked the ac codes twice again tonight, 30 minutes apart. both times tonight it returned code 21. today code 00. does this help?
  • paul29paul29 Posts: 178
    The code 21 is indicating the solar sensor ( black sensor in the righthand windshield vent ) is not sensing light. When checking in dark conditions direct a flashlight or similar light source on the sensor and the code 21 will not appear, from what you've said the sensor is working properly . The 00 indication means no codes in memory . Have you installed the new belt/checked the tensioner ? Also when the system is working , does the engine rpm increase/decrease slowly by about 300rpm when turning the a/c on and off? (approx 600rpm off/900rpm on)
  • wwestwwest Posts: 10,706
    If the engine coolant should rise to 190F then the A/C compressor will be shut down but no fault codes will be registered.

    To test this possibility use a garden hose to spray the radiator/condensor assembly after the A/C shuts down. A/C should restart almost immediately if coolant temp is the cause.
  • pj2323pj2323 Posts: 43
    i did not have a chance to have the belt installed today. will try tomorrow. i did flush and fill with new coolant. the strange thing is as soon as it cuts down and i press the off switch, it starts right back up when i press auto. works perfect on the highway. only time it cuts off is idling and slow traffic, and this is not all the time. thanks for all help. will let you know about the belt and i will try the garden hose.
  • pj2323pj2323 Posts: 43
    in this post you said to close engine and radiator drain cocks,. when i drained my coolant today, i only drained the radiator. where is the engine drain cock located?
  • gee35coupegee35coupe Posts: 3,475
    On the 1994 LS? And should I go back with stock plugs or would the new Iridium plugs or Bosch +4's do?

    It's time for a major tune up.
  • paul29paul29 Posts: 178
    You can see the block drains without taking the under cover off by looking up and forward from the steering rack , near the main o2 sensor but on the block . It has a small pipette pointing down and there is one on each side of the block .
  • wwestwwest Posts: 10,706
    Trac code 19, 92 LS400.

    Installed new rear brake pads, forced piston to retract, fluid level in reservoir rose, trac diagnostic next, code 19.

    Removed fluid to below max line and no help.

    Lots of caution notes regarding overfilling brake fluid reservoir but no information regarding how to fix. fairly sure I have no fluid leaks but "19" says brake pressure pump is cycling too often.

    Anyone else experience this and know what to do to fix?
  • vchengvcheng Posts: 1,284
    Check the ABS sensors and their wiring harness. Also it is better to open the bleed fitting because pushing older fluid that may be contaminated back up the lines may not be a good idea.

    I know you are not a fan of fluid changes, but over 10 years, you'd be surprised to see the level of particulate contamination in brake fluid, not to mention water content.

    I'd suggest a brake fluid flush as well.

    When all else fails, there's always the dealer.
  • wwestwwest Posts: 10,706
    150,000 miles on this one, brake fluid is quite dark, I have always advocated changes/flush at ~100k.

    Diagnostic indicates brake pressure pump is cycling too often. Must be a leak within the system, to the low pressure side say, or accumulator gas pressure side may be "flat".

    But I still don't see how brake pad change, resulting in "over-fill" of the reservoir, could have resulted in this failure.

    Coincidence maybe?

    Dealer would be the last resort, but I'm betting they would simply start out replacing parts, assemblies (pump/accumulator), etc, until the diagnostic doesn't come back.
  • wwestwwest Posts: 10,706
    the weirder things get.

    Parking brake set, firmly, tranx in drive, voltmeter monitoring the output of the Trac brake pressure motor, each time the accelerator is "tipped in" even ever so slightly, the relay enables the brake pressure motor.

    On the tenth "tip-in" the trac failure indicator lights.

    Repeatable even in cruise control on the highway.

    Operationally this is exactly what it should do if on "tip-in" a rear wheel slips, but there is no indication of rear brake application nor dethrottling.

    The ECU is correct, the Trac motor is cycling more often than it should, but why?
  • vchengvcheng Posts: 1,284 errant signal from one of the ABS sensors in the rear?
  • wwestwwest Posts: 10,706
    Jacked up passenger side rear wheel, started engine, put in drive, wheel begins to rotate, applied very light throttle tip-in, Trac applies braking, rapid pulsing.

    Same with driver side wheel only off ground.

    Front wheels thoroughly blocked to prevent movement.

    Does everyone know this thing applies brakes to both rear wheels simultaneously?

    Not just to the slipping wheel?

    How stupid can Lexus be/get?

    Corrected on later models with 4 channel ABS?
  • wwestwwest Posts: 10,706
    I knew that the parking brake warning lamp was "failed" when I purchased the car. Since the speedo and tach needle "lighting" was also in failure mode I bought the entire assmebly from a wrecking yard and installed it yesterday.

    It turns out that in the speedo assembly I removed the Trac failure lamp in the "shroud" above the speedo hade had the bulb removed.

    Now, do I really need a (useless??) Trac system that applies braking to both rear wheels while dethrottling simultaneously, or do I simply remove the bulb in the new assembly?
  • wwestwwest Posts: 10,706
    Comprehension, understanding...

    Trac code 19: "TRAC motor ON and OFF operation is higher than a predetermined number of times (accumulator pressure leakage)."

    Trac code 19: Circuits/devices to check...
    "(1) Fluid leakage in actuators or tubing."
    "(2) Pressure leakage of accumulator."


    Up until just a few moments ago I was assuming "Pressure leakage of accumulator" meant brake fluid pressure leakage.

    Then I remembered that a water well pump short- cycles (repetitively, quickly, on and off, on and off, etc. )if the pressure on the bladder side of the water storage tank (accumulator) is low.

    So now my guess is that each time the throttle is "tipped-in" (from ANY current position) the ABS/Trac ECU checks for sufficient Trac brake fluid accumulator pressure and actuates the pump until the accumulator fluid pressure switch opens.

    With no gas pressure on the "bladder" side of the accumulator the pressure switch would not likely remain open (indicating high accumulator fluid pressure)for very long. But that condition wouldn't be detected until the next throttle "tip-in".

    Ten cycles in a relatively short period and the Trac failure is illuminated and Trac is disabled.

    Sure wish the wording had been "Gas pressure leakage of accumulator".

    Anyone know if Lexus (or anyone) can recharge a Trac accumulator?

    Oh, well, nice relaxing and easy-going father's day.
  • pj2323pj2323 Posts: 43
    paul & west.tried the water hose, did not work. had the belt replaced today , and the mechanic said the tensioner was ok.the ac cut off 2-3 times in his shop after he had replaced the belt.finally it started working with both condensor fans running for 10 min.i shut the engine down, started it right back up and the ac worked for another 10 min. without the fans soon as i backed out to leave, the ac light started blinking. i drove the car 25mi this afternoon to an appt. worked fine until i stopped and put in park. light started blinking.left there it worked fine. parked at wmart and stayed appr 40 min. started engine and compressor, ac started blinking immeditately. switched the ac off and back on, it worked fine. drove 25miles back, with no problems. i left it running in my driveway, and ac still worked. it was a really hot day in ga. today. could the heat cause some sensor to malfunction? how about you q45 man, any ideas?
  • wwestwwest Posts: 10,706

    In hot weather, A/C compressor running, the fans should run at low speed (connected in series, 6 volts each) unless the engine water jacket temperature begins to rise above ~190F, in which case relay act to run fans in parallel, 12 volts each.

    How did you creat the circumstance wherein the fans did not run and the A/C subsequently shut down, therein lies the problem.

    Parked, on a hot day, with the A/C running, if those fans don't run at least in low speed the A/C will shut down due to threatened engine over-heating.

    Also check and make sure the viscous clutch is engaging the engine driven fan, forcing it to turn with the engine. Heat flowing downstream of the radiator increases the vicosity of the clutch fluid thereby tightening the coupling.
  • wwestwwest Posts: 10,706
    the electric condensor fans operated (and not) like that on their own then you have an intermittent circuit connection.

    On the 92 the "high" side refrigerant pressure sensor/switch (controlling low speed operation) is behind the passenger side headlamp assy and the relays or behind the driver side headlamp.

    How many miles?

    You might be losing the brushes (intermittently in one of the fans which would prevent low speed operation and then by the time the engine coolant temperature begins to rise it may already be too late for both fans at full speed to reverse the trend.

    I would actually place bets on intermittent failure of the refrigerant high pressure sensor/switch myself.
  • wwestwwest Posts: 10,706
    car parts feel threatened?

    Went to the auto wrecking yard today and bought a used Trac accumulator (38k mile LS carcuss). On the way home I noticed that the Trac fail indicator wasn't illuminating. Once I got home I tested the Trac functionality in the method under which it failed every time yesterday, ten throttle tip-ins, in drive, with the parking brake set.

    No failures.

    So what gives?

    I'm relatively sure that some past owner knew the Trac was failing and disabled the Trac fail bulb to prevent a new buyer from knowing/noticing.

    On the other hand I was once also relatively sure that my work replacing the rear brake pads had created the failure via excess fluid in the master cylinder.

    Oh, well, now I have a spare Trac accumulator, just in case.

    My plan was to replace the accumulator and have Lexus drain and flush the brake system(s) and reset the airbag code 41 which I apparently caused inadvertantly by switching out the speedo/tach module without disconnecting the battery.
  • pj2323pj2323 Posts: 43
    has 153,000. complete ac system has been replaced within last 3 years. all but condensor. all i did to create the situation was to switch the ignition off, to see if the compressor would start back up. it did, but the fans did not. i dont remember seeing these fans run but at one speed, and that seems to be a high speed. i did not know they are two speed. there is a switch that turns the fans on that is on the dryer. think this switch is ok if it turns them on?
  • wwestwwest Posts: 10,706
    Now I'm betting real money that the refrigerant pressure switch behind the passenger side headlight is intermittently failing. There are three switches/sensor in the one "module".

    1. A low pressure switch that is open if there is little or no pressure in the system. This one prevents the compressor from running at all if there is not enough, or no, refrigerant in the system.

    2. A high pressure switch, ~220PSI, that turns (sw opens) the compressor off once enough liquid refrigerant is accumulated on the pressure side upstream of the evaporator.

    1 & 2 are in series internally to the module, either one open stops the compressor. 4 wires in the connector, one pair for 1 & 2, and one pair for 3.

    3. A medium pressure switch ~100PSI(??) that activates the fans at low speed, series, 6 volts each, when the compressor has run long enough to begin accumulating liquid refrigerant.

    The fourth sensor/switch is within the engine block, water jacket, and causes the fans to run at high speed, 12 volts each, if the engine water jacket temperature begins to climb in spite of the low speed fan operation.

    If the engine water jacket temperature continues to climb even with the fans at full speed then the A/C compressor clutch circuit will be opened to prevent engine overheat.
  • wwestwwest Posts: 10,706
    Suction tube (bulge in this tube under and between the two condensor cooling fans)is covered with rime (white) ice at least 1/4" thick after about an hour of operation.

    The A/C compressor doesn't shut down except if you turn it off somehow or it goes into engine overheat fault mode.

    Refrigerant pressure switch(s)has/have failed.

    Don't know why Lexus does not provide some protection/detection for this type of failure. Ford A/C system used to provide a fusible link between the high side and the low side such that if the pressure difference exceeded a certain value the high pressure due to continuous compressor operation was bypassed into the low side.

    Apparently Lexus just lets the refrigerant keep being pumped until everything is frozen solid all the way to the compressor suction inlet and then the compressor itself fails due to "slugging", liquid refrigerant entering its suction side.
  • paul29paul29 Posts: 178
    The pressure switches in the early LS's are set to operate with pressures encountered with R12 . Are you presently using R12 or R134a ?
  • My 1999 LS 400 just rolled over 30,000 miles. Should transmission fluid be changed at 30,000 miles or just checked? I have heard Lexus recommends changing at 30,000 miles - my manuals say check at 30,000 miles?
  • wwestwwest Posts: 10,706
    the dealer is just out looking for extra coinage.
  • q45manq45man Posts: 416
    What most do and we recommend [since Toyota T4 is an ultra premium product $6 quart] is a simple 3-3.75 quart pan drain and refill. While only 30% gets changed this way eventually enough additives get replentished for it to function.

    The question is how long do you want the tranny to last 100k, 200k, or 300k.
    Replacement will cost you $4800......[5 speed AT].

    Think the $25 plus labor is good insurance every 30k.

    We have many customers with 90-92 LS400 with over 250k on cars same tranny [but this was a different 4 speed unit]. Since tranny was new for 98 not enough years/miles are showing to predicit how the 5 speed will last......YET!
  • wwestwwest Posts: 10,706
    do you think your tranny will last when the cheap mcD type help that dealers hire to perform ROUTINE maintenance leaves the sump pan bolts loose?
  • wwestwwest Posts: 10,706
    IC600, on PCB sub-assembly 177232-0433 appears to be the reprogrammable microcontroller/microprocessor in the 1992 Lexus LS400 climate control module. 42 pin dip, pin 21 grnd, pin 41 & 42 both VCC.


    501A 1109L
    9125 Z41

    "D" is most likely for Denso
    "9125 Z41" is undoubtedly a manufacturer date/batch code.

    IC600 labelling is the same for a 1991 and 1992 climate control except for batch/date codes, 1991 climate control module is "9004 Z13".

    CN7, connector 7, 4 pins, appears to be the programming connector.

    Pin 4 is grnd. Pins 1,2,3 are connected to pins 24, 22, 23, in that order/sequence, of IC600, each through a 200 ohm resistor via IC800 resistor pak.

    Anyone know who actually makes this microprocessor?

    I suspect Toshiba.
  • jeffmust2jeffmust2 Posts: 811
    What do the rest of you think?
  • blkmgkblkmgk Posts: 54
    With the help of a mechanic from lexus(who works for my friends shop), we were able to diagnose my sound that comes from upfront when I go over a bump. I need to replace the right side lower ball joint. The shop charges at least $400-500. I could get the part for $76.00. Is this a simple install for myself? Do i need special tools? Whats involved? Someone got details?
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