How to test tps sensor???

Following...

 

Don't know about using a multimeter, but my Scangauge 2 can give throttle position readings.

Scangauge Digital Gauges features

Perhaps you can get a similar reading from another OBD2 BT adapter and app combo. This one mentions TPS.

BAFX Products – ANDROID – OBD2 Scanner Bluetooth Code Reader & diagnostic Tool –

Posted via the PriusChat mobile app.

 

The section about the TPS

 

I don't know, you have not specified what the problem is, you just asked how to measure the operation of the TPS.

 

Before you changed the pedal, was it intermittent to begin with? P2135 is NOT likely to be related to the pedal, since Prius, like many vehicles these days, are 'fly by wire.' There is no physical connection between the pedal and the the throttle.

The ECM reads the position of the pedal, and determines what the throttle should do/where it should be (opening wise). That relationship is not 1:1 like a simple throttle cable opening/closing the throttle plate in car like the Prius, and many things go into the cars calculation of how much to open/close the throttle.

P2135, as you stated is specifically EITHER:

There is a difference between the output voltages of VTA1 and VTA2 of 0.02v or less for 0.5 seconds or more

OR

The output voltage of VTA1 is 0.2v or less, AND VTA2 is 1.75v or less for 0.4 seconds or more

With the trouble area indicated as a short between VTA1 and VTA2, TPS, or ECM.


In other words, the problem causing the code is not caring about the pedal/pedal position - which is why I asked if it is/was intermittent (you just happened to replace the pedal when things are OK).

It appears that there is a short (in the sensor or harness wiring), the throttle body itself (I don't think you can get the TPS separately), or a bad ECM. You can try cleaning the throttle body to see if it's sticking, but I REALLY don't think that's going to cure your ills because even if the plate was sticking, the ECM would still see the proper voltage differences so the code you would be getting would be different (the throttle not being where the ECM expects it to be).

 

Just following up (curious) if the error has ever came back since you swapped the pedal.

 

To keep things clear for any future readers who might land on this thread:

The car has both a throttle position sensor (under the hood, connected to the throttle) and a pedal position sensor (under the dash, connected to the pedal).

The two sensors are independent.

The pedal and the throttle are independent ("drive by wire"). Pushing the pedal doesn't directly move the throttle at all. The pedal sensor is an input to the power management control ECU. The ECU decides how much power the driver wants, how much to use the battery for, and how much to use the engine for. It notifies the ECM of the wanted engine power, and the ECM decides how much to open the throttle.

The two sensors are similarly built. For redundancy, each one has two separate Hall sensors and produces two separate output voltages.

For the pedal sensor, those are called VPA1 and VPA2, and they go to the power management control ECU.



For the throttle sensor, they are called VTA1 and VTA2, and they go to the ECM.




To better detect malfunctions for safety, each sensor's two output voltages are not identical. Each sensor's two output voltages track each other, but one is higher by a certain specified voltage. The car's firmware checks both signals for having the right mathematical relationship to each other, and will log a code and enter a failsafe mode if they don't.

You can see the pedal sensor is a bit more strictly redundant. The throttle sensor shares one power and one ground for both of its Hall sensors, but in the pedal sensor, each Hall chip even gets its own separate power and ground.

Toyota really does not want any pedal sensor malfunctions giving wrong input about the driver's intentions.

The trouble code situation is very confusing. Codes P0120, P0121, P0122, P0123, P0220, P0222, P0223, and P2135 pertain to the throttle position sensor. Codes P2120, P2121, P2122, P2123, P2125, P2126, P2127, P2128, and P2138 pertain to the pedal position sensor. You can see these ranges overlap weirdly, so the similar looking P2135 and P2138 codes are codes about completely different sensors and come from different ECUs.

Scan tools that identify the source of a trouble code are helpful. If you are using something like Techstream, or the Car Scanner phone app, where it not only shows trouble codes but also which ECU each code came from, you'll see that any P2120, P2121, P2122, P2123, P2125, P2126, P2127, P2128, or P2138 came from the power management control ECU (so it's about the pedal sensor), or that any P0120, P0121, P0122, P0123, P0220, P0222, P0223, or P2135 came from the ECM (so it's about the throttle sensor).

The fortune cookies for the codes are just as confusing as the codes themselves. All of the above codes have fortune cookies that look like "Throttle / Pedal Position Sensor" something something. They don't identify one or the other.

That's because all of these codes are in the P0 or P2 ranges that are standardized by SAE, so they use more generic language than Toyota could have used in a manufacturer-defined range.



So SAE defined a list of standard codes for "throttle" or "pedal" position sensors having different circuits named A, B, C, D, E, etc. Toyota decided to use "A circuit" and "B circuit" to mean VTA1 and VTA2 (the throttle sensor signals), and "D circuit" and "E circuit" to mean VPA1 and VPA2 (the pedal sensor signals). Hence the confusing names.

Upthread here, jdjd reported a P2135 code, and tak1313 gave the correct information that P2135 is about the throttle sensor (under the hood), not the pedal sensor (under the dash). But jdjd replaced the pedal anyway, and reported an apparent improvement.

That kind of thing does happen amusingly often in a forum. There's usually a reason why replacing the wrong thing led to an apparent improvement, and in some cases the reason eventually comes to light, and in others it never does. But future readers can save some time and effort by paying careful attention to which codes have to do with which sensor.

 

Was P2135 the ONLY code, or was there another code - like P0123 or similar?

 

That's most likely the explanation right there. P2138 is definitely about the pedal sensor.

 

As @ChapmanF indicated - there is significant difference between P2135 and P2138. P2135 is directly related to the TPS sensor in the throttle body. P2138 is a correlation code. In this case, the expected position of the throttle position is not what they system is expecting based on the pedal position.

 

That's not even quite it. P2135 and P2138 are both correlation codes. What P2135 means for the throttle sensor is exactly what P2138 means for the pedal sensor.

Each of these sensors, for safety redundancy, makes two different voltage outputs. For the throttle sensor, those are VTA1 and VTA2. They are supposed to track each other, like this:



If they don't, you get the P2135 code. It's about failed correlation between VTA1 and VTA2, which are both from the throttle sensor. (Shoehorning the check into the SAE standard codes, Toyota picked P2135, which is about correlation between voltage "A" and voltage "B".)

For the pedal sensor, its two outputs are VPA1 and VPA2, and they are supposed to track each other, like this:



If they don't, you get the P2138 code. It's about failed correlation between VPA1 and VPA2, which are both from the pedal sensor. (Shoehorning the check into the SAE standard codes, Toyota picked P2138, which is about correlation between voltage "D" and voltage "E".)

There isn't any code comparing an "expected position of the throttle" to the pedal position. Because the system is drive-by-wire (and the engine is only one source of driving power, and the ECU decides how much to use it), there isn't any simple "expected position of the throttle" based on the pedal position.

 

My bad - @ChapmanF is correct. When I posted about the P2138, I had limited access to my stuff, but a coworker had the Fixd app. I copied the code from the FSM for my Tacoma (which I fully had), but used the description from the Fixd app (I just had my coworker send a snip (I don't use Fixd):


Just got home and checked the Prius FSM, and his description is correct (more accurate related to the Prius).

 

Kind of shows how, even in the DTC ranges that are "standardized" by SAE, that might not really "standardize" much.

For Gen 1 Prius, Toyota used P1120 as the pedal sensor code. That's in the P1 manufacturer-defined range, so they could give it a perfectly clear fortune cookie, "Accelerator Pedal Position Sensor Circuit Malfunction" and four different INF codes giving the low-down, and there was nothing confusing about it.

At the same time, there were SAE standard codes P0120 and P0121 with generic SAE fortune cookies Throttle/Pedal Position Sensor/Switch "A" Circuit Malfunction, and Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance Problem. The wording is so generic you don't know if it's about the throttle or about the pedal, or if it's a sensor or it's a switch, or what the "A" circuit is. Toyota used those codes for the throttle position sensor, but you could get wrong guesses all over the place if you're not looking in the Toyota manual.

By the time of Gen 3, SAE had gone and defined a bunch more standard codes, all with the same hyper-generic "Throttle/Pedal Position Sensor/Switch" but for circuit A, B, C, D, E, and so on.

So Toyota went ahead and realigned their throttle-sensor codes to use the new standard codes for "A" and "B" (the two VTA outputs from the throttle sensor). And they gave up their old, nice, perfectly clear manufacturer-defined code for the pedal sensor, and instead used the new generic codes for "D" and "E" (for the two VPA outputs from the pedal sensor).

So now the fortune cookies for the throttle codes and the pedal codes are all the same "Throttle/Pedal Position Sensor/Switch" mumbo-jumbo, except the ones with "A" and "B" are about the throttle, and the ones with "D" and "E" are about the pedal. I'd say that wasn't a step toward more clarity.

Why did they skip "C"? I think SAE expected that some sensors might have three outputs. In addition to the code for miscorrelation between "A" and "B", there's one available between "B" and "C" and one between "A" and "C".

Likewise, in addition to the standard P2138 code for miscorrelation between "D" and "E", there's a P2139 for the same between "D" and "F", and a P2140 for the same between "E" and "F". (It's like somebody forgot these things are hexadecimal: in between P2139 and P2140, all of P214A/B/C/D/E/F all mean other unrelated stuff.)

Toyota's sensors just have the two signals, so they called the throttle signals "A" and "B" and skipped "C", and called the pedal signals "D" and "E" and skipped "F".

I haven't run across any standard SAE codes for correlations between these groups (say, comparing "A" to "D"). The idea seems to be maybe two independent sensors that might have up to three outputs each, but the independent sensors don't get compared to each other.

That makes me suspect that even that description from Fixd is just somebody's wrong guess that got immortalized in the app. The code wouldn't mean what Fixd thinks, unless there's a car somewhere whose manufacturer decided to call the throttle sensor "D" and the pedal sensor "E" (or vice versa).