Code P1120 is code for malfunction of APPS (Accelerator Pedal Position Sensor).
This pedal position sensor (APPS) have a dual output inverse of each other, a redundancy for safety reasons. Cost of sensor on line ($270, at Lexus $400)
Be aware, there are two sensors on throttle body.
First one (closer to front of vehicle) is for throttle servo motor (don’t touch it!).
Second one (closer to firewall) with accelerator pedal cable attached to it is one what causing the problem. I replace several of those APPS sensors.
Because I'm specializing in automotive electronics troubleshooting, I took all of them a part.
By doing so, I discovered on all of them common problem, what fortunately is an easy fix. Malfunction of that sensor is caused by improper cleaning of organic solder residue during manufacturing of sensor. This organic solder is very aggressive and after years of exposing this solder to harsh environment, acid in that solder causing self-destruction of solder what result of it is so called "cold connection". Manufacturer ignored (perhaps intentionally) basic rule about cleaning contacts after soldering and protect it against moisture by covering soldered area with some kind of protective layer what is very common in automotive industry (shame on Toyota).
SOLUTION:
Fix is very easy and can be done in less than hour include dismount and mount of sensor. To do so, just make small opening in to white plastic cover at location where is connector (see my picture).
By creating opening, you will create access to soldering points.
VERY IMPORTANT!!!
Apply new solder to existing points and take it all out (use desoldering tool or cupper mash to do so).
By doing this you will remove old solder and expose contact from connector.
Now you MUST clean those contacts by using very sharp knife and scrape old oxide layer from those contacts.
To verify if you did good cleaning, you will see after scraping nice shiny brace contacts. Second verification is, that when you apply new solder on those contacts, it will perfectly cover it with solder. If you will see solder creating small ball and not covering entire contact, you need repeat process again till you get perfect join solder to contacts.
Next step is just nicely resolder all 4 contact to PC board with non-organic solder (best is solder with Resin flux), but if you don't have solder with Resin flux, you can use solder with organic flux (same as Toyota used) but you will have to use warm water to clean soldering points to remove any organic residue to prevent from same mistake as Toyota did in first place.
After drying up inside soldered area (use hair dryer) to prevent from moisture entering in to this part, you must cover opening (in white plastic) with good tape or any kind of non-conductive sealant (best is clear non-conductive silicone).
If you use silicone to cover opening, be very careful do not overfill inside opening, otherwise you will create restriction for potentiometer to freely move.
After silicone dry up, you can install your APPS and enjoy it.
If you did good job, you will not have problem with this part for entire life of that car.
If you have any question, you can e-mail me at: sekcov@yahoo.com
Peter
