Lexus P1120, brand new OEM Sensor Bad?

Mike Technician Atlanta, Georgia Posted   Latest  
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Driveability
1999 Lexus GS300 3.0L (2JZ-GE) 5-spd (A650E)
P1120

This Lexus came in with CEL and the complaint of "won't go over 25". I scanned and got P1120, Accelerator Pedal Position Sensor Circuit Malfunction. The car was not in limp mode when I pulled it in. I performed the tests in AllData for the code, as well as inspecting the connector for the sensor and the connector at the PCM, all clean and tight. I load tested the circuits as well. All good.

I put my lab scope on the 2 signal wires (VPA and VPA2 I think) and as the vehicle warmed up, they started to show dropouts in the signals, first on one then on both. So I condemned the sensor and a new one was ordered from Lexus. Once the dropouts showed bad enough on both VPA and VPA2, the car did go into limp mode which I found when I went to pull it out.

When I got the new sensor I installed it and cleared the code. CEL came back on immediately with P1120 and the car stuck in limp mode. So I went back through the procedure in AllData with the new sensor. Everything checked out, VPA and VPA2 were good; I did watch them both on the scope. but P1120 refused to clear and the car stuck in limp mode. I still had the old sensor so I reconnected it and cleared the code and had throttle control again. Then I reinstalled the old sensor so I could drive it while we wait for a new sensor. Now the CEL comes on intermittently with P1120 but no limp mode.

One other test I found and performed after this went down. It's not in the procedure for P1120, it's I think under 'component tests and general diagnostics' when you click on Throttle Body in AllData. Don't hold me to that, but I'm pretty sure that's where it is. That test says to check the resistance between pins 3 and 4 (E2 and VC). Spec is 1.2k-3.2k ohms. The original sensor measured 1.6k. The new one was 2.7k. both are in spec, though the new sensor is obviously closer to the high end of the spec, so could that possibly be a problem?

Lexus is giving us a hard time about warrantying out the sensor, they said there's nothing wrong with it. They ohmed E2 and VC and rejected warrantying it. And no one else has one. Shop is going to be stuck buying one out of pocket and fighting to get a refund later if at all. And now it's got me doubting myself a little. I want to be good and sure I'm not missing something. Any recomendations?

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Anura Educator
Auckland, New Zealand
Anura Default
 

Hi Mike, Did you re-learn the APPS by using the scanner? If answer is NO please give it a go.

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Mike Technician
Atlanta, Georgia
Mike Default
 

There is no option for that in my scanner (Verus Pro 19.2) I also did not see anything in AllData nor Identifix about a relearn procedure for the sensor. The only reset option I have in my scanner is 'Reset Memory' but that states it resets the learning value for the automatic transmission control in the ECM so not sure if that's what you are talking about.

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Hollis Technician
Boulder, Colorado
Hollis Default
 

Hi Mike, did the new APP sensor code immediately with or without movement / stroke / sweep of the accelerator pedal ? Can you source a used APPS relatively cheap and easy for comparison ? Yeah, I know 50% chase of getting a bad one. Apples to oranges but I had a new OE APPS on a 2015 Subaru fail within 20,000 miles, so anythings possible. The sensor design is a Hall-Effect type (I think that's…

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Mike Technician
Atlanta, Georgia
Mike Default
 

It codes immediately, no movement required. I didn't write down the voltages but they were in spec. I will try to get it back in this afternoon and get some numbers for this thread.

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Richard Instructor
Palmetto, Florida
Richard Default
 

What does scan data show? I understand you tested the wiring, but what does the ECM think it sees? Toyota has a pretty complete test procedure for that code and I know its in Alldata. It starts with looking at scan data to try a determine a diagnostic direction. see attached pic....

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Mike Technician
Atlanta, Georgia
Mike Default
 

Unfortunately Snap On does not have pids for the voltages from the APP sensor. I can only get the voltages by probing the wires.

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Richard Instructor
Palmetto, Florida
Richard Default
 

Go to the global/generic side of the scan tool and see what you can look at. I’m pretty sure it should be there

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Mike Technician
Atlanta, Georgia
Mike Default
 

Not in global either. Snap On is removing pids. I've noticed a couple vehicles lately where there's data pids I used to see that are gone now.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

It's good to keep a few ten year old scan tools around for dealing with the twenty year old cars. Complete Mastertech kit, would be OE for that car, and can be had now for the price of a Verus update, and it would have shown the correct data. Not saying it's a wise financial decision for you in your position, but throwing it up for all the guys reading along that think latest is always…

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Mike Technician
Atlanta, Georgia
Mike Update
 

Guys, we ordered another sensor from the dealer and it worked perfectly. I still wish I knew exactly what the PCM didn't like about the first new one but at least the car is fixed.

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Hollis Technician
Boulder, Colorado
Hollis Default
 

Cool! Dissect the old one, let's get a look inside, if you care too.

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