Anatomy of Gen III Fly By Wire TPS

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ionbeam

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[Pre-Edit -- FU Photobucket, to view the photos you will need to install one of these addons Firefox fix Chrome fix ]

Starting in '13 the FJR got a Fly By Wire throttle body system. As part of the TB updates, a new design Throttle Position Sensor was added and moved to the left end of the throttle body rack. By 2016 it is looking like there are some of the new design TPS which are going bad. red2kcbr diagnosed his driveablilty problem as a bad TPS and changed it with a new part. This fixed his driveablity problem so it strongly indicates the TPS was defective, red2' sent me the TPS so I can take a look at it.

The physical construction of the TPS is different than the previous type used on all cable controlled throttle body racks but the electrical design remains the same.

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. Edit on 9/7/16 -- Fred W's TPS seems to prove that this is not a date code, meaning now unknown. The FSM says the TPS should be 1.20-2.80 k Ω and the sensor output should be 0.63-0.73 V at idle. The old TPS had only one output, this TPS has two outputs. This is the schematic view of the TPS:

i-Q4KDS3C.jpg


The colors of the pins in the connector correspond to the wires. The sensor (item 103) has two resistors in parallel with two wiper outputs. The blue wire is a +5 reference voltage from the ECU and the Black/Blue wire is reference voltage ground. The right side of the diagram is the ECU, the wires make no other stops between the sensor and the ECU. The resistors in the bad TPS measured 1.86 k Ω The wiper value went from 0.380 Ω to 1.86K Ω which is correct for the part.

Top view of the TPS with a blue dot. Dunno what if anything the dot signifies. The metal sleeved holes allow the TPS to be slightly rotated to calibrate it for idle voltage.

i-bBGpxcf-X2.jpg


This side connects to the long center rod that the throttle plates are connected to and it is different than the previous TPS connection. The center pivot rotates 90°. As the throttle plate rod turns it rotates the wipers inside the TPS in lock-step with the plates. The lobes of the center pivot are not symmetrical so it can key onto the throttle plate rod in only one way.

i-dfFV2Cm-X2.jpg


Here is a family picture when the sensor is taken apart.

i-XSntsfT-XL.jpg


The item in the upper left is the cover for the sensor, the green arrow points to the self centering pivot that keeps the wipers turning in circular alignment. The orange ring on the right is a weather seal that goes between the cover and the body of the sensor. In the center of the picture is the main body of the sensor. The yellow arrows point to the wipers which ride along the resistor patterns and pickup a varying voltage off of the circuit. The back side of the plate with the wipers is the keyway which goes on the throttle plate rod. In the upper right is the resistor board, it is upside down, it normally faces down over the wipers. I had to clip the leads which leave the board and go to the connector pins. The blue board is in two layers, the pins connect to the resistor material with an internal connection at the squares which the red arrows point out.

i-Dghmqxr-XL.jpg


As the throttle plate rod rotates the wipers are dragged along the resistor trail. When the wiper is at one end of the trail it sends ~.0680 volts to the ECU. The ECU converts the voltage to a digital value, does some math and recognizes this as the throttle plates being 17% open. This is the 17 you can read in DIAG when testing the TPS. As the throttle is opened up the wiper voltage goes up to ~4.5 volts, the ECU does some math and recognizes this as the throttle plates being 100% open. The voltage should linearly go up and down as the wipers slide over the resistors.

Pictures showing what is wrong with the resistors was problematic to get. The resistors are failing the exact same way as the TPS that I had in my '04 even though they are different physical materials. Picture attempt #1 to show the worn resistor material issue in a way that retains relationship to the part:

i-2gb3Q2T-XL.jpg


The arrows point to spots along the resistor where the wipers have cut into the resistive material. Once the resistor material gets thin and/or cut it becomes very susceptible to heat causing the resistor value to drift causing erroneous voltages or the wiper simply makes no contact and the voltage drops below 0.680 V which the ECU sees as closed throttle plates. The voltage climbs as the throttle is opening, the ECU sees the throttle opening 20%, 25%, 30% then suddenly going to 0% then as the wiper gets back on good resistor material it suddenly jumps from 0% to 35%. You feel like the throttle was cut and then snapped open creating a really rough ride.

Picture #2 below is taken at an angle so the glare can show just how cut up the resistor material has become:

i-GPr6Gbc-XL.jpg


The deepest wear happens where the throttle is most commonly used. Typically it is at idle and then roughly at 30%-40% of throttle opening where you cruise. The failure of the TPS is a slow wear-out and not a sudden break down. Edit to add: The right side pair of wipers go from the bottom of the sensor (idle) up to the top (WOT). The left side goes from the top (idle) to the bottom (WOT). Both right and left resistor tracks had heavy wear from idle to ~40% throttle.

Beginning TPS failures may only show symptoms when hot, and this is hard to diagnose; as the TPS continues to degrade it will become easier to measure the failure. red2's TPS had failed, yet at room temperature measuring static resistance it tested good. The Gen III Yamaha Diagnostic Tool should allow a dealer to data log the TPS signal which should immediately and clearly show a failing TPS. Unfortunately, this kind of failure will normally pass DIAG and a passive resistance check.

If there really is a fundamental problem and Yamaha starts seeing lots of failures caused by the materials the TPS is made from there will probably be a Technical Service Bulletin (TSB) put out and a Rev. 2 TPS made available. If the issue is related to a date code, manufacturing plant or batch the TSB would instruct a dealer on how to inspect the part for the code (or dot color) and replace any TPS within the problem batch.

 
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Great work!!

I hope that this is the answer to Bill's problem (and that Yamaha gets off its ass to fix it).

As far as problems are concerned, this one is pretty minor but very frustrating. Perfect explanation as to why the issue gets progressively worse as time goes by.

 
Kind of interesting how one side wore more than the side 180 degrees from it. It's almost seems like the wiper spring was stiffer, or maybe the way the throttle shaft put pressure skewing it to one side perhaps?

 
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Kind of interesting how one side wore much more so than the side 180 degrees from it. It's almost seems like the wiper spring was stiffer on one side...
Or, it's a problem with the photographer that noted it was difficult to get a good picture :)

 
So, this has me thinking even more than I already did that Bill L's problem is just a bad TPS.

With all the crap he's going through at that dealership, and waiting for the entire throttle body from Yamaha, I'd be really, really tempted to just throw a new TPS in and be done with it. Then send Yamaha and the shop a bill for the warranty work.

edit - I'm really glad that these apparent 3rd Gen problems are something as relatively easy to fix as a TPS. Something most of us are capable of fixing if it happens to us.

 
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Kind of interesting how one side wore much more so than the side 180 degrees from it. It's almost seems like the wiper spring was stiffer on one side...
Or, it's a problem with the photographer that noted it was difficult to get a good picture
smile.png
So it's even wear both sides?
For clarification I've added this to the post: Edit to add: The right side pair of wipers go from the bottom of the sensor (idle) up to the top (WOT). The left side goes from the top (idle) to the bottom (WOT). Both right and left resistor tracks had heavy wear from idle to ~40% throttle. The right side resistor track was fractionally more worn than the left side resistor track. The conical center pivot pin should keep the wiper force pretty even.

It would seem that the resistor material needs to be more durable or the wiper less damaging. Because the TPS is used in a motor vehicle there needs to be sufficient force between the wiper and resistor so that NO bounce, jounce, bash or vibration would cause the wiper to bounce off the resistor.

TPS failures have been common in all vehicles regardless of wheel count but recently I haven't seen as many car TPS go bad.

 
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THANK YOU, PROFESSOR IONBEAM. This contribution is why I enjoy our community so very much. Where else are you going to find this?

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I see the wipers are "tongue-ended" with tines like a dinner fork. Rubbing or sliding in one direction will be smooth; in the other direction, wouldn't it lead to gouging action? If the wipers were curved, convex-side upward, the rubbing and inevitable wear should be less harmful to the resistive surfaces.

Like other similar rotating devices, any unlubricated sliding parts will lead to scrubbing/scratching/scoring and eventual failure.

 
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Yammy needs to develop a diag procedure for this part / issue, either using their software, or even with a dmm using the correct pin out that the dealer techs can follow. If it shows up good under one position, the resistance will soon go wonky as the rotor position changes. Not all dealer techs are sharp enough to know what to look for, but if they had a procedure to follow, well even a trained monkey can follow that.

 
I see the wipers are "tongue-ended" with tines like a dinner fork. Rubbing or sliding in one direction will be smooth; in the other direction, wouldn't it lead to gouging action? If the wipers were curved, convex-side upward, wouldn't the eventual rubbing and wear be less harmful to the resistive surfaces?
Like other similar rotating devices, any unlubricated sliding parts will lead to scrubbing/scratching/scoring and eventual failure.
The TPS in my Gen I used this type wiper, note that I bent out one of the brushes to show the construction:

Dscn0013sm.jpg


 
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+1 above.

Apparently, some engineering intern designed the Gen3 TPS wipers.

 
Its sad that there is a mechanical wear item like this in the system.

OTOH thankful for the redundant potentiometers which prevent the ECU from receiving errant data causing a runaway condition.

 
THANK YOU, PROFESSOR IONBEAM. This contribution is why I enjoy our community so very much. Where else are you going to find this?
............................................................................................................................................................

I see the wipers are "tongue-ended" with tines like a dinner fork. Rubbing or sliding in one direction will be smooth; in the other direction, wouldn't it lead to gouging action? If the wipers were curved, convex-side upward, the rubbing and inevitable wear should be less harmful to the resistive surfaces.

Like other similar rotating devices, any unlubricated sliding parts will lead to scrubbing/scratching/scoring and eventual failure.
If it's like the wipers I've dissected, they will have a curved ending, sometimes the contact point is a stamped rounded dot. Like Alan said, the resistive material is a wearable item and is prone to eventual failure. But that doesn't mean they couldn't use an improved more wear resistant material with a higher cycle count rating.

 
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...Apparently, some engineering intern designed the Gen3 TPS wipers.
The TPS designer got the brushes/wiper mostly correct but used a thick (depth) but very soft, rubbery resistor material that cut quite easily, the end result was a TPS that failed for damaged resistor material.

For a coupla bucks more it is possible to screen a glass/metallic thick film resistor onto a ceramic base and fire at 850° to make a very hard resistor material that is thermally stable.

 
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Yammy needs to develop a diag procedure for this part / issue, either using their software, or even with a dmm using the correct pin out that the dealer techs can follow. If it shows up good under one position, the resistance will soon go wonky as the rotor position changes. Not all dealer techs are sharp enough to know what to look for, but if they had a procedure to follow, well even a trained monkey can follow that.
One problem with diagnosing is that the potentiometer may actually test OK under static testing, or in Diags, only to screw up with added vibration and/ or heat. I believe that ionbeam tested this one with a meter and it looked "OK" before he tore it apart. We had the advantage of knowing that this particular one was bad because replacing it fixed the bike's problem.

+1 above.
Apparently, some engineering intern designed the Gen3 TPS wipers.
Its a certain bet that is a generic TPS used in many other vehicles.
Yes, no doubt. Like many modern manufacturers, Yamaha didn't design nor manufacture this TPS. They buy them off the shelf, to their requirements, and then adapt the FI system to their use. Even within the Yamaha parts structure this part number is used on 3rd Gen FJRs and 2009 and later V-Max. If they are crappy you'd expect that the Vmax crowd would have become aware of it first.

Hopefully, like in the 1st Gen TPS failures, there will be an improved design TPS. Whether there is a recall or not will be determined by how wide spread the problem is. Just having a better one to put in there in its place, in the event of a failure, would be a very good thing, IMO.

 
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As mentioned at the beginning of the autopsy, the Gen III TPS tested good in every way when sitting on my bench. Just like the TPS that came out of my Gen I. I only found my Gen I TPS by putting a volt meter on the sensor, putting the DMM on my handlebars and going for a ride. It was the heat and vibration of the ride that clearly showed the TPS voltage dropping from 0.900 volts to 0.300 volts then bouncing back up to 1.20 volts in sync with a horrible engine response that showed it was the culprit causing the dirveability issue.

It was clear what was happening when I opened up that TPS. The Gen III TPS looks the same as far as the resistor material being cut and burned.

The only good thing about troubleshooting the TPS is the very consistent failure symptom when riding. As you accelerate the voltage climbs, the ECU reads that and provides appropriate fuel injection and spark timing then suddenly the voltage drops to 1/2 idle causing the fuel to be cut off (instant deceleration), then the wiper advances back into good resistor material and like a light switch the fuel injection goes from below idle to 40% throttle. BANG (or is it BAM?). It happens so quickly that the decel/accel may not be obvious but the event feels major bad.

 
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