P1128 Throttle Control Motor Malfunction

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

maingear

maingear

Joined
Jun 10, 2007
Threads
11
Messages
123
Hey everyone! Long time lurker, guess it's time to actually post something...I have a 2000 LX470

Removed and inspected throttle body components. Cleaned and reinstalled. Worked fine for about a month.

on the 5th of July, P1128 popped up again. I only have the manufactures maintenance manual volume 1 (plus alldata at the library) and followed DI-117 with no results. Removed Throttle Control Motor (TCM), Installed new TCM ($280). It takes a couple of minutes for the computer to throw the code, or simply tap the throttle twice.

I will ring out the wires to the ECU to ensure proper values and ensure throttle position sensor is at 15 degrees at closed position.


With nothing better to do, I replaced the Throttle position sensor and the accelerator sensor. I rang out all wires before changing components. Oscilloscope and voltage readings are fine until trouble code is logged.

Removed the throttle body, cleaned, inspected - looks / operates like new.

Could it be an obstructed catalytic converter? All data did not show any SBs but I don't like using it as a referance.



Total spent on parts so far - $620
Not having a car payment and the pleasure from working on the car myself - Priceless
 
Hi Maingear,

I am not sure if I have the same problem, but I have a 2000 UZJ 100 with about 110,000 KM on the odometer. Last weekend the orange "check engine" light came on the dash so I took it to the local Toyota service center here in Bangkok. The technician informed me that I should replace the "Body Assy Throttle" (name of the part that showed up on their computers). Is this the same part that you are mentioning here? They didn't give me the error code so I don't have that. The mentioned part costs about USD 1,400 here excluding the labor and any taxes.

I do notice a lag in the acceleration of the truck every once in a while. But that light disappeared since my last Toyota visit.

Would appreciate any comments from your experience.

Thanks,
Chad
 
Keep the old parts, they may be serviceable.

My LX470 has 130,000 Miles.

The throttle valve assembly can be removed and inspected for proper operation. There was no blockage, defect in operation, or debris build-up on this part. Replacing my throttle body seems senseless the more and more I studied this issue.

I threw parts at it because I didn't know what the proper resistance should be to determine their standard condition, also do to its intermittent nature. Voltage and amperage input was not specified for a bench check, to isolate them from the system to see it they will fail. There should have been a test where the valve's torque, at the shaft, can be measured with a torque wrench (equipped with a dial type indicator), an adapter would be required for this test.

Basically if friction caused by the rotation of the valve increases to the point where it causes excess forces (increasing electrical demand) for the throttle control motor, the ECU will kick over to "Limp Mode" and there will be a great loss of power, rough shifting, and abnormal pedal travel before an increase of RPM.

If the voltage/amperage received from the magnetic clutch or throttle position motor is too high (or too low) the ECU will log a malfunction and "limp".

The only way to verify is to check wires from the ECU to the component in question, by unplugging the ECU and the part and ensuring voltage is passing through without resistance and voltage is not leaking out to ground or surrounding wires on the harness.

I found that my wires were serviceable. Next I monitored electrical activity with an oscilloscope. The service manual gives a picture of the desired condition.

The signal looses its gain when the engine logs the malfunction. I do not know if this is because a transistor is at fault, or if this is proper activity for "Limp Mode"

I would like to see if an ECU swap would resolve my issue. Transistors are responsible for the base signal and one could overheat due to a defect and be the origin of this nightmare (I have my eye on my father in law's tundra, could that ECU be the same as mine?)

 In short, I found that in this case, the trouble code is only a clue as to which system is effected, not the malfunction of a specific component. At this point, I can not isolate a part or wire and produce a failure. As good mechanics we strive for the root cause as efficiently and quickly as possible. This is very frustrating.
Additional comments welcome

good luck chad
​
 
chadiln said:
I am not sure if I have the same problem, but I have a 2000 UZJ 100 with about 110,000 KM on the odometer. Last weekend the orange "check engine" light came on the dash so I took it to the local Toyota service center here in Bangkok. The technician informed me that I should replace the "Body Assy Throttle" (name of the part that showed up on their computers). Is this the same part that you are mentioning here? They didn't give me the error code so I don't have that. The mentioned part costs about USD 1,400 here excluding the labor and any taxes.
Click to expand...

Check out the FAQ entry on Throttle Position Sensor / Accelerator Pedal Position Sensor problems for a lot more information.

I'm going to add this thread to the FAQ thread as well since Maingear has shared some nice tech. :cool:

maingear said:
I would like to see if an ECU swap would resolve my issue. Transistors are responsible for the base signal and one could overheat due to a defect and be the origin of this nightmare (I have my eye on my father in law's tundra, could that ECU be the same as mine?)
Click to expand...

Unfortunately all the 100s have been produced in the "bad caps" (http://www.badcaps.net/) era. We can only hope that Toyota boards have fewer problems then others and they don't seem to be failing at a high rate. But I would carefully inspect the capacitors on any problem/suspect board.

I doubt the ECUs are identical but .... I'm sure they are very similar.

Lets us know what you find.
 
Last edited:
Yes, Thank you very much MainGear. Sounds like replacing the Throttle Body Assembly won't solve the problem since it may not be the root of the problem. I am not mechanical nor technical when it comes to cars/trucks... so bear with me.

Would an aftermarket "engine management unit" solve this?

I have seen these reprogramable boxes that piggy back on the original ECU that supposively give better fuel efficiency while boosting hp when installed.

And thank you again NMuzj100 for the FAQs and links!
 
Update

A 4x2 ECU from a Tundra does not work on a 3/00 LX470. It sounded like injection/ignition timing were off.

The throttle body and all parts attaching to it will fit on the first generation Tundra. I installed my throttle assembly and the Tundra ran fine. This confirms that he issue is isolated to the harness and or ECU.

I rang out all the wires again. Labeled connector's pins to agree with the factory repair manual - everything was exactly as published.

Removed ECU and visually inspected it again. No bad caps or cold solider joints found. It was in excellent shape.

This is the last act of a desperate man, DO NOT ATTEMPT!!!
There was dust on the board. I did not have enough alcohol to clean the board with so I chose to use dish detergent and warm water to do the cleaning. I did not mind sacrificing my ECU because there is something wrong with it. Cleaned the case in the same manner. After using a soft brush and giving a through rinse, I dried with warm air and reinstalled.

The engine ran perfectly. During a 15 minutes test drive the exact same P1128 tripped the ECU again.

I guess that water may have completed the circuit for a poor solder. I am waiting for the soldering iron to heat up, so all the connections can be re-heated.
 
Engine Running Fine Now!!

I guess there was water still on the board or my solder needed a once over. (The pins to E6 and E7 were only heated) I gave it 36 hours to dry and all my issues are gone!! No trouble codes.

Everything is finaly back to normal.
 
Throttle Assembly replaced.

I ended up replacing the Throttle assembly in my UZJ 100 yesterday. The whole process took a couple hours and the truck runs perfectly.

Truck feels much lighter, especially during inclines (over bridges and overpasses) and doesn't require much peddle travel.

The technician had a spare ECU but he said that it wasn't necessary to replace my old one.

Total bill = USD 320.00
 
maingear - Did you ever compare the Tundra and 100 ECUs ?

Glad you both got your problem resolved.
 
maingear said:
This is the last act of a desperate man, DO NOT ATTEMPT!!!
There was dust on the board. I did not have enough alcohol to clean the board with so I chose to use dish detergent and warm water to do the cleaning. I did not mind sacrificing my ECU because there is something wrong with it. Cleaned the case in the same manner. After using a soft brush and giving a through rinse, I dried with warm air and reinstalled.
Click to expand...

Is it okay to just use a can of compressed air to clean out the board? I may want to clean out the board in case mine is dusty too.
 
chadiln said:
Is it okay to just use a can of compressed air to clean out the board? I may want to clean out the board in case mine is dusty too.
Click to expand...

Static electricity is very damaging I would use the canned air and not compressed "shop air" I was sure to ground myself/board and water pipe properly before the first drop of water touched the board.

A fast evaporating, non residue liquid (safe on metal and plastic) works best. For best results one should use a contact cleaner or circuit board cleaner. I like using 91% alcohol in a sure-shot. A spray bottle should work as well.


NMuzj100 said:
maingear - Did you ever compare the Tundra and 100 ECUs ?
Click to expand...

The 4x2 tundra ECU did not work however all of the connectors did hook up. It sounded like the ignition/injection was off. My LX470 was manufactured before April 2000 so the later ECUs would not work (timing, etc). I did not think to have the Tundra key's antitheft RFID chip in the LX. I should have taken the battery out if the LX key and hold the Tundra key over the ignition switch, where the antenna is.
 
Last edited:
It looks like this thread hasn't updated in awhile. I have a '99 LX470 with 190K on it. We've had the "limp mode" issue a few times but it hasn't tripped in several years now. Recently did the O2 sensors and P1128 was lurking in the codes. Traced that back to these threads. However, it looks like the limp mode is more directly tied to P1120/1121 (think those were the codes I saw on another thread).

I replaced the TPS the other day just b/c its cheap. I just slid it around in the slot until I got the idle where I wanted it. I saw some mention of calibration but that doesn't seem to be necessary.

Not experiencing the limp mode condition, but it is throwing that 1128 so I am wondering if I should be looking for parts? If so, is the verdict that the code is mainly caused by the manufacturing defects (bad capacitors) in the ECU and therefore I should throw money down the drain on the accelerator sensor? Is that on the one on the left side with the coiled accelerator cable? On my truck, the locking clip is busted off so it just slides on.

Any suggestions? This truck has been awesome for us. In almost 200K miles, just winding up our 3rd set of tires, 4th set of brake pads and the only failures have been:
1) Bad fuel injector at 100K -dealer fix
2) Leaking rear axle seal around 140K - dealer fix
3) steering column interlock snapped (casting) around 150K - I replaced myself
4) Window support (plastic) snapped around 75K - I fixed myself with piece from an auto glass shop
 
UPDATE!!!!!

Cleaning the ECU fixed the issue. The board was not dry. Toyota engineering is so precise that particles of dust will conduct electricity and affect data. The LX470 has well over 200,000 Miles on it and only the starter's contacter/plunger has been replaced (do to the starter not working - separate issue).

Here comes the difficult part. After 15 years of marriage my wife decided to call it quits. She got the LX400 and the pain was unbearable. I truly miss that vehicle!!!

On the brighter side, I have purchased a 79 fj40 project. Pics will be posted for my build. The previous owner has the engine overhauled, old man E springs, disks on the rear, upgraded diffs, boxes of bolts shipped in, and a factory new five speed. He has spent a ton of money on this project, it just needs minor sheet metal work done under the body. I have a lot of reading to do, don't know jack about the fj40. Justin
 
maingear said:
UPDATE!!!!!

Here comes the difficult part. After 15 years of marriage my wife decided to call it quits. She got the LX400 and the pain was unbearable. I truly miss that vehicle!!!



Priceless quote!!! Made me laugh - not at your situation - just the way you phrased it...a couple my buddies were in your same situation....well at least you have a new project...thx for posting your results-it will definately save some people $$.
Click to expand...
 
:lol: yeah it was a joke, but I really do miss the LX470. The repair shop saw her comming and got her good on a botched brake job twice. Karma?
 
Back to the ECU swap. The ECU has an antenna wire. Antenna is a black plastic ring surrounds or is near the ignition key switch. The ECU will ping the passive RFID chip in the key that is entered in the ignition switch..... so install the other ECU, take the key's body apart as if you were replacing the battery in the key. Place the ECU's doner key (this has the RFID that will make the doner ECU happy) near the antenna as the stripped key is inserted and turned to start, the ECU will time the ignition to the proper degree for normal operation. If it works and you want to keep doner ECU, move the antenna & zip tie the key under the dash near the antenna. My ex went to change the key's batt and the car wouldn't start. ECU wasn't happy without the proper RFID.
 
hi all . to fix this code p1128 on toyota land cruiser .check on the driver side fuse box . remove the fuse box and check on the back side of the fuse box . you will get the relays . change the relay and ears the code and enjoy the driving:):p
 
nadeemnoor said:
hi all . to fix this code p1128 on toyota land cruiser .check on the driver side fuse box . remove the fuse box and check on the back side of the fuse box . you will get the relays . change the relay and ears the code and enjoy the driving:):p
Click to expand...

So while in Colorado to go snowboarding, my 00 LC with 225k miles decided to stay in limp mode and throw code 1128? I would clear codes and then it would just happen again. It finally just started working again and hasn't happened again over the past 2 weeks. I'm up for cleaning my ecu @maingear or replacing a relay if this would work? Any suggestions? Thanks
 
July 2007 I washed the ECU in the kitchen sink. 2018 my ex wife is torturing me by still driving the lx470, she got in the divorce, to work every day. It has over 300,000 miles on it now and cranks every time the first time.

I would recomend anyone with this trouble code to pull the ecu first and clean it with a Electrical Contact Cleaner Spray as the first step in the trouble shooting sequence. There is no protection for the ECU’s circuitry to keep dust away in dusty environments.
 
I’m just here to give thanks to maingear and testify that cleaning the ECU as a first step fixed this for me. Hell, i’d recommend everyone clean their ECU pre-emptively.

Full story: Sunday I had the wife and kids loaded up ready to go for an adventure, after LC had been mostly sitting a few weeks. We made it about a mile down the road, and suddenly no power at all and had to coast off to the side of the road. The CEL would’ve been lit right before it died if I didn’t already have the CEL lit for other reasons. Well after figuring out it’d go if I mashed the gas all the way down, i limped it home and switched cars. Ran codes later, new P1128. Tried cleaning throttle body. Throttle operated ok by hand. Tried drying wet spot with big fan on driver floor a couple days, as it could relate to mystery relays on drivers side. But None of that helped. I could take it up and down our road about a mile before p1128 and dead again. After reading here, went ahead and pulled ECU, which was actually sparkling clean on the inside. No sign of dirt, but I still sprayed it down with QD electronic cleaner really well, and dried off with compressed air. It fired up easy, and no problems since. I’ve driven it back and forth to work 3 days now, hoping this is solved with no money spent.
 
You must log in or register to reply here.

Similar threads

S
ECM battery malfunction after replacing battery
Replies
11
Views
1K
sleepdoc
S
G
100 Series ABS/Traction Control (?) Issue
Replies
6
Views
574
badlander
B
B1oodyBuzzard
AC control buttons
Replies
4
Views
643
Mike NXP
Mike NXP
usinglinux
  • Question Question
Intermittent Rough Idle with No Revving/Throttle Response
Replies
3
Views
407
usinglinux
usinglinux

Users who are viewing this thread

Total: 1 (members: 0, guests: 1)

Share this page

Back
Top Bottom