Code P1121 accelerator position sensor....need some advice please (2 Viewers)

flintknapper

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99 LX 470 (198K)

Wife called me just awhile ago...said the LX 'lost power' while she was on her way to work this morning.

Said vehicle had a CEL. Took my scanner and hooked it up. Got a P1121 code.

Getting ready to look at it and read up about it, but for those who can offer any advice before I get started, it would be appreciated.

I'm guessing I will looking at either the TPS or the APPS?

Are there any tests I can run on these to help pin-point the source. I don't yet have a FSM for this vehicle.

Thank You in advance,

Flint.
 

suprarx7nut

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I had the same problem. It was the APPS for me. If I just restarted the car it was fine. Happened one time, freaked me out, but I kept driving. Happened again a week later and I grounded it until I fixed it. Not a big deal sitting in traffic, but could be a HUGE deal if it died mid turn, crossing a highway or something.

The online dealers were impressively cheap compared to my local dealer.
 

flintknapper

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I had the same problem. It was the APPS for me. If I just restarted the car it was fine. Happened one time, freaked me out, but I kept driving. Happened again a week later and I grounded it until I fixed it. Not a big deal sitting in traffic, but could be a HUGE deal if it died mid turn, crossing a highway or something.

The online dealers were impressively cheap compared to my local dealer.

Took a look at my throttle body, its nice and clean. Disconnected and cleaned the connection on the APPS, reconnected with a dab of dielectric grease. Adjusted throttle cable (it had more slack than is necessary). Ordered a Toyota TPS (89452-30140), going to replace that first. Then if the problem re-occurs....I'll do the APPS.

I looked at the real-time engine data with my scanner and didn't see anything out of order. If it happens again after replacing the TPS, then I'll know where to look next (APPS). The trouble with that set up...is that if your APPS fails (completely) you may not be able to continue on in limp mode depending upon where you are, which almost warrants keeping a spare if you are far from help.

The symptoms in my case were not as severe as some I have read about. My wife said the vehicle suddenly acted as if it was losing power and the CEL light appeared, so she pulled over right away and called me. She did not turn off the engine. When I arrived, I scanned it (real time data) and checked the code (P1121). Cleared that code and had my wife drive the vehicle home.

It did not give any problems on the drive home. So we will see.
 
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I would take the throttle body off itself and clean the throttle blade and surrounding area with a brass brush and cleaner (along with everything else your doing)...It gets filthy in there and perhaps the throttle blade can get stuck momentary..
 
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flintknapper

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I would take the throttle body off itself and clean the throttle blade and surrounding area with a brass brush and cleaner (along with everything else your doing)...It gets filthy in there are perhaps the throttle blade can him up and stuck momentary..

I had the TB off less than a year ago and thoroughly cleaned it then. I looked at the bore and throttle blade yesterday and it is pretty much spotless still, but your recommendation is a good one...since the trouble code I had (P1121) can be thrown as the result of the sensor being out of 'range' for any reason.

This is one of those things that requires a little detective work because a number of things can be the cause for the fault.

For my year model (99) it could be a dirty TB (particularly the bore or throttle blade), sticky throttle cable, TPS, APPS, Wiring, Connectors, TB motor or magnetic clutch.

The 'easy' fix (if the problem persists) would be to replace the entire throttle body with the most recent (for year model) electronics (TPS/APPS). In my case....I'm thinking I will end up having to replace the APPS, but am starting with the TPS more as a matter of maintenance. Then if I need to do the APPS I will have a new TPS already in place and the old one as a spare.

Alternately, a TB from an '01-02 Tundra....I believe will fit my 99 LX470 and could be used as a replacement. These could be sourced (used) from a salvage yard if needed a low cost replacement or a 'spare' for certain year models.
 

suprarx7nut

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Help my understanding here. Doesn't the code represent a poor electrical signal? Isn't the plate and TB bore completely isolated from any portion of the electronic circuit? Is the mechanical cleanliness a concern because the plate could hang up and register a mismatch in throttle positions between the TPS and APPS?
 

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