AllStrFame

Two months ago after a rather rainy day, while accelerating uphill on a freeway entrance ramp, I hit a rather large puddle and my 1999 LS400 with 166K started a dramatic slide. The VSC beeped, kicked in and immediately corrected the issue and no one was the wiser, no lights, everything seemed normal. Two miles later I parked the car, went to an hour long meeting, and then returned to the car. The CEL came on upon starting and approx ten seconds later the VSC light came on. I had a OBD2 reader and it read P1126 which turned out to be the magnetic clutch circuit malfunction code. I reset the CEL and both CEL and VSC turned off the remainder of the trip. Tested out VSC with some hard driving and the system beeped and kicked on like normal, no lights present. Next time I fired the car up, CEL and then VSC turned on. Read same P1126 code but did not reset it; three drives later both lights kicked off and remained off for a few days until one morning they both popped back on. When I manually reset the CEL, snow mode and power mode work normally, just not when the CEL and VSC lights are on. If the CEL and VSC lights are off, I can use the VSC OFF button and it works normally. This has been happening intermittently for several weeks now and after reading through several hours of forum, I am unable to determine if the issue lies with the TPS, the ECU, wiring in between, the actual throttle control unit or if there is really an issue with magnetic clutch. I am looking for any one with thoughts on what could specifically be causing this, based on the symptoms I have described. As electronic components for this car are expensive and non returnable if installed, I am hesitant to make a guess at which component is the culprit. Thanks in advance for any insight you can provide.

PureDrifter

iTrader: (10)

it sounds like a TPS/APPS issue. Try using your code reader to read PENDING codes (codes that are close to triggering a CEL, but havent yet). if you see a different code it will shed light on which sensor is going bad/out of adjustment.

P1126: Magnetic Clutch Circuit Malfunction, this is the clutch between the throttle motor and throttle valve. So most likely you will see a code for either the TPS or APPS going too.

AllStrFame

It has been a few months and the symptoms have remained consistant. I have been monitoring as suggested on a frequent, almost ocd basis, however I fail to get any codes other than the P1126. The CE/VSC light still turns on only intermittently, and only when the engine goes from an off to an on state. It never trips while driving. I scan and check for codes several times a week but nothing besides P1126 ever shows. I have removed and cleaned the throttle body and all accessible parts to no avail. This LS starts, runs, idles and accelerates with no issue with the light on or off. The only thing that doesnt work when the light is on is the VSC/Traction control, and and soon as I reset the CEL, it immediately works as designed. Any other thoughts on the specific source of these symptoms?

PureDrifter

iTrader: (10)

sounds like the throttle body needs to be replaced...though it could also be the VSC ECU.

I think you need to have it diagnosed by someone familiar with the testing procedures for the ECU (multiplex system and all), magnetic clutch/Throttle motor, and TPS. these are electrical components, cleaning them after they've apparently failed won't magically bring them back to life.

Rockatansk

Where is the VSC Ecu located? Is it integrated in the main ECU ?
Perhaps you have some simple problems like corrosion on the contact surfaces?
Check all the connectors and plugs/cables to and from the throttlebody

AllStrFame

I will trace the wires this weekend and see if can spot any corrosion. What primarily kills me about this issue is that : 1. If I use my OBD2 interface to reset it, everything immediately starts sorking normally and then stays working for for ths next 1 - 20 times I drive the car. It might fail over between the next time I stop and then start the engine and even if I reset it every time, there is really no rhyme or reason to it. At this point I have resigned myself to thinking moon cycles might be the key.

The other bummer is that all the local scrapyards don't separate the above mentioned parts from the engine, so I can't even justify rolling the dice and getting the most probable part here locally.

GS4_Fiend

iTrader: (22)

P1126 Causes:
-Open/Short in magnetic clutch
-Bad magnetic clutch
-Motor clutch is stuck

burteboy

since you try another ecm and throttle body the with the process of elimination you have a broken wire between the computer and the throttle body connectors. you have two connectors 1 throttle position sensor and accel position sensor.the accel sensor. Each connector has 4 wires. Now the if you can trace the wires to the computer, il look at a diagram and let you know tomorrow. In the meantime you can just hold each wire firmly and give it a thug to check for any break. disconnect your battery get your ohm meter and connect one end to the pin at he connector and the other at the computer. i think you connector is the second connector from the end. Look at the wire colors and it would be easy. try and let me know.

ALLS

I had the exact same problem described in the original post for close to two years in my 99 LS400. CEL and VSC illuminated on start of ignition, lasted for days or weeks, then turned off on its own. Or, I could reset the code with my tester to turn it off. Whenever I tested it, the code was always the pesky P1126. Other than the VSC being deactivated when the CEL/VSC was illuminated, the engine ran absolutely the same as normal. Once the light went off (either on its own or from me resetting the code), I could go for days or weeks without it turning on again.

I searched several times online for an answer. Every time I searched I ended up at this thread, which is the only thread I found that described my problem exactly. But the original poster never returned to explain what, if anything, he did to solve the problem. So, I was not sure how to proceed. First I thought it might be bad wiring since that is what the Lexus mechanic's notes say and is also suggested in this thread. I had my independent mechanic check all the connections. I also did this myself and sprayed them with an electrical connection cleaner. Nope, still had P1126 problems. Next, I took my best guess on what parts were failing and ordered the following parts from parts.com: (1) 89452-30140, which is a Throttle Sensor (Apprx $75); and (2) 89672-47010, which is a Throttle Control Motor (Apprx $292). Had my independent mechanic install these new parts. P1126 has now been gone for 4.5 months. It never previously stayed off for more than a month. I had thought that perhaps only the second of the two parts would have done the trick, but it made sense to me to spend the extra $75 just in case it was the throttle sensor.

If installing the parts in the preceding paragraph didn't do the trick, my next step would have been (a) live with it or (b) replace the ECU (ECM).

Anyway, the problem was annoying and apparently fairly uncommon, so I joined this forum just to post what worked for me. I have long been a member of the other Lexus forum but this one seems to have much more traffic. Hope this helps someone. I'd be interested to know if the original poster solved his or her problem.

Oh, just one other cautionary note. A weak battery can cause all manner of error codes, at least in an LS400. The LS400 system does a diagnostic routine quickly at the time of starting the engine. If a component does not have enough juice to perform the diagnostic routine properly, an error code will trip - not because the component is failing, but because it didn't have enough electrical power to properly run the diagnostic. If the owner doesn't know that the culprit might be a weak battery, they could start needlessly swapping out expensive parts. When I first developed the P1126 problem I assumed that it was the battery. Unfortunately it wasn't.

Thanks to all who post their problems and solutions. I've owned 6 LS vehicles so far and have benefited greatly over the past 17 or so years from these forums.