Anatomy of Gen III Fly By Wire TPS

[RaYzerman19]

Good job on the analysis, Alan. The wear would indicate the symptoms likely occurred in the area of wear. The good news as you say is a slow deterioration rather than a catastrophic failure.

In Bill's case, I would also vote for a TPS replacement, keeping in mind the acceleration position sensor is a similar sensor and if a new TPS didn't cure it, that might be next on the list. I'm still surprised Yamaha is choosing to replace the TB's rather than look at these two parts first.

 

[Constant Mesh]

Does the throttle servo have a built-in position indicator which sends info back to the computer? How many external wires connect to the servo?

It's probably not the accelerator sensor simply because the problem occurs while in cruise too. In cruise the accelerator sensor remains at the minimum resting position -- it's not moving.

One could conduct a very interesting test using the cruise in this case.

Initiate cruise. Set it at 65 mph. Run for a while at that speed then cancel cruise but retain the setpoint.

Let the bike coast down to 50 mph or so and then press "resume".

Observe how it accelerates back up to 65 on computer control.

 

[Fred W]

Does the throttle servo have a built-in position indicator which sends info back to the computer?

Yes, that would be the TPS. In addition to getting throttle position for calculating the fueling, it would also be used to send position info to the Fly by Wire. In fact, that may be the reason that there are now two wipers in the 3rd Gen TPS: One to the FI, the other to the YCCT.

The "Accelerator Position Sensor" only tells the ECU where you have the right hand grip turned to. It is the "command" for the YCCT.

How many external wires connect to the servo?

2. + and -, both directly from the ECU

 

[Constant Mesh]

One could perform an experiment by modifying the TPS circuit.

I believe the TPS is a 5 K ohm variable resistor. A basic 0 to 5 volt voltage divider circuit.

One could add an external 2 K ohm resistor in series with the circuit. Divide 5 volts across 7 K ohms.

You'd have to adjust the idle position of the TPS to compensate for the additional 2 K ohms.

This would allow the TPS wipers to operate in a different position than before.

If indeed the TPS was at fault the problem would occur at a different throttle opening than before -- a more closed throttle position.

 

[mcatrophy]

Question: Since there are two potentiometers, presumably both giving nominally the same voltage to the ECU, why isn't the ECU programmed to flag an error when wear causes one to give a significantly different voltage from the other? Strikes me it would be trivially easy.

 

[JAB]

I'm curious. How many miles were done on this TPS?

Thanks!

 

[red2kcbr]

Just shy of 25k miles on that TPS.

Alan, excellent analysis and write-up. Thank you; it's good to know the problem was real.

I've put 3k miles on the new TPS, all good so far.

 

[RossKean]

Just shy of 25k miles on that TPS.
Alan, excellent analysis and write-up. Thank you; it's good to know the problem was real.

I've put 3k miles on the new TPS, all good so far.

22,000 miles left in it...

 

[BigOgre]

red2kcbr diagnosed his driveablilty problem as a bad TPS and changed it with a new part.
-----

The bad TPS that red2' sent me was P/N 2S3-85885-00. It had a date code stamped on the side -- Date Code 4314E which is the 43rd week of 2014; the E may be a plant or batch code.

I've put 3k miles on the new TPS, all good so far.

Was the new TPS the same part #, have the same markings, etc?

 

[08FJR4ME]

88K on my original TPS but I fear it is on it's way out on my bike also. I am getting a more pronounced herky jerky lately. So we have torn apart a Gen1 and Gen3 TPS. Are the Gen2 significantly more reliable? If I change it out I will donate it to Alan.

Just Sayin,

Dave

 

[escapefjrtist]

Great information and TPS autopsy ionbeam.

Let's hope MamaYama recognizes the problem and comes out with an updated design. With the miles many of us accumulate on FJRs, it's not a matter of if - but when.

--G

 

[Fred W]

Question: Since there are two potentiometers, presumably both giving nominally the same voltage to the ECU, why isn't the ECU programmed to flag an error when wear causes one to give a significantly different voltage from the other? Strikes me it would be trivially easy.

It's not clear from the FSM how the two signals are used inside the ECU. From the back seat, it makes all kinds of sense to have the two signals be redundant and compared in the ECU and then (after validation) split the signals to the functions of fuel injection calculation, and FBW throttle control (including cruise functions).

But it also may be that the second potentiometer is used for the (new in 2013) FBW control feature and the two signals are not ever compared to each other. Thee were always only one wiper on the TPS prior to 2013. This would explain why no fault codes would occur when a TPS is on the way out.

However, the APS (Accelerator Position Sensor) also has redundant potentiometers, and it really only has one function (Throttle command). None of the functional descriptions in the FSM explain the purpose of the duplicate signals from these sensors.

 

[mcatrophy]

Question: Since there are two potentiometers, presumably both giving nominally the same voltage to the ECU, why isn't the ECU programmed to flag an error when wear causes one to give a significantly different voltage from the other? Strikes me it would be trivially easy.

It's not clear from the FSM how the two signals are used inside the ECU. From the back seat, it makes all kinds of sense to have the two signals be redundant and compared in the ECU and then (after validation) split the signals to the functions of fuel injection calculation, and FBW throttle control (including cruise functions).

But it also may be that the second potentiometer is used for the (new in 2013) FBW control feature and the two signals are not ever compared to each other. Thee were always only one wiper on the TPS prior to 2013. This would explain why no fault codes would occur when a TPS is on the way out.

However, the APS (Accelerator Position Sensor) also has redundant potentiometers, and it really only has one function (Throttle command). None of the functional descriptions in the FSM explain the purpose of the duplicate signals from these sensors.

It just seems strange to me that a couple of lines of code could give a fault indication, something like
if (mod(voltage1-voltage2))>ALLOWED_TPS_DIFFERENCE) {

error(TPS_ON_THE_WAY_OUT);

}

 

[Fred W]

Just shy of 25k miles on that TPS.

Oh crap. I've got 20k on mine now.

Maybe we'll have to start changing TPSes when we do the valve checks?

At a hundo a pop, that is not a welcome routine maintenance item.

 

[ionbeam]

If the TPS turns out to have a 25k mile fuse Yamaha will be seeing 1) a lot of TPS being sold --or-- 2) a whole lot of throttle body assemblies being replaced (sorry Bill Lum). In the past, high part consumption seems to trigger a TSB and upgraded parts, I would expect Yamaha to step up and do the same here.

It remains to be seen if the failing TPS have the same date code or if the basic design just isn't working out in the FJR. Since the date code of the deceased TPS is the 43 week of 2014 (Mid October, 2014), has there been any 2013 FJRs with failed TPS?

 

[rPGoatBoy]

Might be worthwhile to wander over to the VMax forums and have a look because they've been using the same part number TPS as the Gen III FJRs since 2009 when the Vmax got updated. Judging by the p/n it looks as if there has not been a revision to the part.

 

[Bill Lumberg]

Excellent writeup ion. Mine tests good consistently, but exhibits the problem you describe in operation.

 

[wheatonFJR]

Griff has a higher mileage 14 with 50k on the clock...I don't recall him saying anything. But maybe he doesn't turn the throttle thingy.

 

[griff]

Griff has a higher mileage 14 with 50k on the clock...I don't recall him saying anything. But maybe he doesn't turn the throttle thingy.

No, I just draft you

. Actually, I have had a stumble or two, but many miles ago and it hasn't reappeared.

 

[Geezer]

Question: Since there are two potentiometers, presumably both giving nominally the same voltage to the ECU, why isn't the ECU programmed to flag an error when wear causes one to give a significantly different voltage from the other? Strikes me it would be trivially easy.

It's not clear from the FSM how the two signals are used inside the ECU. From the back seat, it makes all kinds of sense to have the two signals be redundant and compared in the ECU and then (after validation) split the signals to the functions of fuel injection calculation, and FBW throttle control (including cruise functions).

But it also may be that the second potentiometer is used for the (new in 2013) FBW control feature and the two signals are not ever compared to each other. Thee were always only one wiper on the TPS prior to 2013. This would explain why no fault codes would occur when a TPS is on the way out.

However, the APS (Accelerator Position Sensor) also has redundant potentiometers, and it really only has one function (Throttle command). None of the functional descriptions in the FSM explain the purpose of the duplicate signals from these sensors.

It just seems strange to me that a couple of lines of code could give a fault indication, something like
if (mod(voltage1-voltage2))>ALLOWED_TPS_DIFFERENCE) {

error(TPS_ON_THE_WAY_OUT);

}

What's that funny stuff? Write that in assembler and I might understand what you are saying.

Back on topic, I have seen similar variable resistors used in many things that fail the same way. I think Ionbeam has the right answer when he says that they could provide a much more durable part if they spent an extra dollar or two. Now I wonder if the more durable part actually exists and could be used by someone willing to pay the price.