Annoying Cruise Control problem

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Pin_Head

Pin_Head

10 Year 15 Year 20 Year OG
Joined
Feb 6, 2002
Threads
29
Messages
15,436
Location
OC, CA
96 Lexus Lx450
The problem is that if I try to turn the cruise control main switch on (the button at the end of the lever) at speeds above 45 MPH, the cruise control never comes on, the indicator light blinks 5 times and the ECU sets a #12 diagnostic trouble code. It also won't turn on again until I turn the key off and restart the engine.

It will always turn on at speeds below 45 MPH and it will operate normally at any speed once it turns on successfully.

The FSM says that DTC12 indicates over current at the magnetic clutch or no signal on the brake switch line for 0.8 seconds or more. It also says the potential culprits are the actuator, brake switch and ECU in that order. The brake switch and electrical connection to the actuator check out good according to the troubleshooting guide in the FSM. I doubt it is the ECU because it works fine after it turns on.

Since this problem is not a big deal if I can learn to remember to turn the switch on before I get on the freeway, I am reluctant to go through all the trouble shooting of the actuator, since the FSM just says to replace it if it fails.

Has anyone run into this problem and if so, are there any easy fixes short of replacing the actuator?

Thanks for thinking about this!
 
I have a similar issue, except it will die everytime I enable it around 65-70. I can set the cruise at 60 and be fine, but no higher. I've also had times when going over a bump or rough bridge seam, that the cruise stumbles and trys to correct itself and then die. I still have not fixed it or figured it out. I have done the yanking and lubricating of the cable at the accuator, but it didn't seem to help. But if others have found solutions, I'm looking for them too.
 
I don't know if this applies to your situation, but I had all sorts of cruise control gremlins in a '97 FZJ80 that were "cured" when I replaced the master cylinder with OEM that included a new cap and sensor.My .02
 
Try this: with the truck off, pop the plastic black top off the actuator/motor. It is the "box" on the passenger fender where the cruise control accelerator cable originates from. Grab the gear where the cable attaches on top of the cruise control motor. Cycle the cable and gear 10X or so. If you are doing it right, you will be moving the throttle on top of the engine from idle to wide open 10 times.

I was told that this will clean off the build-up of carbon on the inside of the cruise control motor/module. I have to do this to mine when I don't use the cruise control often enough. Gets it working for me every time. Hope it is this simple for you too.
 
For some reason many folks don't realize that the FSM has a *very* detailed and helpful diagnostics section for the cruise control system. There's even a simple way to get it to flash codes on the "cruise" light, just like the ECU flashes codes on the "check engine" light. Makes it a snap to exactly pinpoint the cause of the problem.

Curtis
 
Thanks everyone! If I get ambitious, I will try cleaning, lubricating and cycling the actuator. I will post up the results if I do.

The FSM has very good trouble shooting diagrams and directions for everything, but even if I go to all that trouble it just says replace the unit if it doesn't check out. This is a little too expensive for me at this point when it works fine as long as I remember to turn it on below 45 MPH.
 
elhombre said:
Try this: with the truck off, pop the plastic black top off the actuator/motor. It is the "box" on the passenger fender where the cruise control accelerator cable originates from. Grab the gear where the cable attaches on top of the cruise control motor. Cycle the cable and gear 10X or so. If you are doing it right, you will be moving the throttle on top of the engine from idle to wide open 10 times.

I was told that this will clean off the build-up of carbon on the inside of the cruise control motor/module. I have to do this to mine when I don't use the cruise control often enough. Gets it working for me every time. Hope it is this simple for you too.
Click to expand...

I think I'll try this in the next 10 minutes, hope it works.:beer:
 
elhombre said:
Try this: with the truck off, pop the plastic black top off the actuator/motor. It is the "box" on the passenger fender where the cruise control accelerator cable originates from. Grab the gear where the cable attaches on top of the cruise control motor. Cycle the cable and gear 10X or so. If you are doing it right, you will be moving the throttle on top of the engine from idle to wide open 10 times.

I was told that this will clean off the build-up of carbon on the inside of the cruise control motor/module. I have to do this to mine when I don't use the cruise control often enough. Gets it working for me every time. Hope it is this simple for you too.
Click to expand...

Actually, cycling the black arm does nothing, as the arm merely pivots back and forth on the shaft (notice the nut doesn't move). The one you want to cycle is the silver arm with two tabs that is below the black arm. This is the one that is attached to the shaft and will move the contacts inside the actuator.
 
Pin_Head said:
The FSM has very good trouble shooting diagrams and directions for everything, but even if I go to all that trouble it just says replace the unit if it doesn't check out. This is a little too expensive for me at this point when it works fine as long as I remember to turn it on below 45 MPH.
Click to expand...

:confused:

No it doesn't.

The diagnostics procedure I'm referring to is done right from the driver's seat. You turn the key to ON but leave the motor off, put the CC system in diagnostics mode, and then start checking each individual circuit/component via flashing codes. It's incredibly easy and *very* cool. That's how I pinpointed the speed sensor as my culprit; plenty of other folks have used it to find trouble in the control stalk itself, or the brake circuit, or whatever.

Again, you must not be looking at what I'm referring to.

Plus, there's more: there's even a special test for when your CC goes out or won't engage while driving (like what's happening in your case). You pull over, *don't* shut the rig off, jumper a couple terminals in the check engine terminal (for OBDI, at least), and the cruise light throws a code teling you why it wouldn't engage.

It's all free info, and the tests are painless to perform. :meh:
 
Cycling the actuator takes no ambition. Only about 5 min. It will likely clear things up for you.
 
CJF said:
:confused:

No it doesn't.

The diagnostics procedure I'm referring to is done right from the driver's seat. You turn the key to ON but leave the motor off, put the CC system in diagnostics mode, and then start checking each individual circuit/component via flashing codes. It's incredibly easy and *very* cool. That's how I pinpointed the speed sensor as my culprit; plenty of other folks have used it to find trouble in the control stalk itself, or the brake circuit, or whatever.

Again, you must not be looking at what I'm referring to.

Plus, there's more: there's even a special test for when your CC goes out or won't engage while driving (like what's happening in your case). You pull over, *don't* shut the rig off, jumper a couple terminals in the check engine terminal (for OBDI, at least), and the cruise light throws a code teling you why it wouldn't engage.

It's all free info, and the tests are painless to perform. :meh:
Click to expand...

No it doesn't what?

Perhaps you didn't read the original post?

My original post indicates that I did all that wonderful and easy diagnostics stuff which pointed me to the actuator, brake light switch or ECU. I checked out the brake light switch and the electrical signals to the actuator from the ECU according to the FSM trouble shooting guide and they are fine. That leaves me with the actuator as a probable cause. My point is that diagnosing the actuator is involved and if it fails, The FSM only tells me to replace the actuator, rather than how to repair it. I wanted to know if there is any easy way to repair it rather than just replacing it.

Your problem was different with the speed sensor. The DTC indicates that my speed sensor is fine.
 
96r50 said:
Actually, cycling the black arm does nothing, as the arm merely pivots back and forth on the shaft (notice the nut doesn't move). The one you want to cycle is the silver arm with two tabs that is below the black arm. This is the one that is attached to the shaft and will move the contacts inside the actuator.
Click to expand...

Problem solved!

It finally stopped raining long enough for me to go outside and take a look at it.

The spring loaded arm below the one that the cable is attached to was sticking. I worked it back and forth 10 times, but it was still sticking, so I put a couple of drops of light machine oil on it and worked again until it turned freely. Took it out on the freeway and tested it 3 times at 70 MPH and it worked every time.

The FSM needs to have the first line on the actuator trouble shooting guide say to check this and put a couple of drops of oil on it it it is sticking. The bastids just want to sell new actuators.

I owe everyone. :beer:
 
Congrats! I will say though that chances are good that the problem is deeper inside the actuator. If the silver arm felt sticky it may have been caused by the old grease inside the actuator gumming up. If it happens again, John (John E Davies on mud) has a lot of good info on his site here: LX450 Technical

I rebuilt my actuator last weekend using John's writeup as a guide and it feels much smoother now (although I don't think it was causing my problem, I wanted to rule it out)
 
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