[Zack66]

FreeSSM is showing 0 signal from the turbine 2 sensor at all times. It is also faulting w/ no turbine 2 signal.

Is the sensor not replaceable? I don't seem to be able to find one with a Google search.

Thanks.

 

[avk]

The problem was reported in the past. According to FSM, the sensor is hardwired into the valve body harness, hence the whole harness needs to be replaced which involves removing the pan. Looks like a skilled person should be able just to cut and splice.

 

[plain OM]

5-speed AT has two torque converter turbine sensor signals. These are not the vehicle speed sensors.

Based on logs that rasterman shared with me some time ago, the turbine 2 signal should show up in RR at all times; that is, whenever the engine is running, transmission is in gear, and the car is moving (wheels turning). The turbine 1 data shows only when the transmission is in 4th gear.

I understand from the FSM that the turbine 1 sensor can be replaced on its own, but the turbine 2 sensor is part of the valve body.

What fault code are you getting? P0715, P1710, or some other one?

What are the symptoms?

 

[avk]

There's another sensor mounted inside the extension housing (not on the valve body). Not sure which is which in FreeSSM. If "no. 2" is the rearmost one, then it's the one mounted outside the case but not available separately from the harness.

 

[plain OM]

Rear vehicle speed sensor is on the outside, toward the rear of the extension case. It has a connector, so can be disconnected from the transmission harness, and replaced, without disassembling the transmission.

Front vehicle speed is mounted on the back of the main transmission case, but is covered by the extension case when it's installed. So the extension case has to be removed to gain access to the sensor. Also, the wires from the sensor pass through an opening into the main transmission case where there's a connector at the valve body that connects the sensor to the main transmission wiring harness. So both the extension case and the pan have to be removed.

Turbine speed sensor 1 is on the outside of the main transmission case, on the left side, near the front. It too has it's own connector and can be removed without disassembly of the transmission.

Turbine speed sensor 2 is on the valve body, and the whole assembly has to be replaced as a unit -- apparently separate parts of the valve body are not available from Subaru.

FreeSSM and Romraider (logger) should display all four signals as well a number of other parameters (see table of PIDs attached) although turbine speed signal 1 is non-zero only in 4th gear. (Turbine speed sensor 2 is monitoring the front planetary carrier rotation, while turbine sensor 1 is monitoring the front sun gear rotation. In 4th gear the two should turn together. In other gears, the front sun gear is held by the front brake, and it's sensor signal is zero.

The factory service manual has a troubleshooting sequence for both sensors in the 5AT Diagnostics section.

 

[avk]

Here's the wiring diagram. Somehow, it doesn't even show "turbine sensor 2", only "turbine sensor 1". So indeed it must be lumped into the "control valve assembly".
It does not show an individual connector for the rear VSS (page WI-57). That could have changed over the years.

 

[plain OM]

What year is that wiring diagram from?

In any event, I think the issue is the turbine speed sensor, not the VSS.

 

[avk]

The manual is for 2006 model year.

 

[plain OM]

2008 FSM is different. The wiring diagram shows the rear VSS with a connector and the front vehicle speed sensor as part of the control valve body, as well as the two turbine sensors. See jpg attached.

 

[Zack66]

5-speed AT has two torque converter turbine sensor signals. These are not the vehicle speed sensors.

Based on logs that rasterman shared with me some time ago, the turbine 2 signal should show up in RR at all times; that is, whenever the engine is running, transmission is in gear, and the car is moving (wheels turning). The turbine 1 data shows only when the transmission is in 4th gear.

I understand from the FSM that the turbine 1 sensor can be replaced on its own, but the turbine 2 sensor is part of the valve body.

What fault code are you getting? P0715, P1710, or some other one?

What are the symptoms?

This is a 2008 2.5 XT

I don't recall the specific code. I didn't realize FreeSSM would dump the data when shut down. but it was no signal from Turbine 2 was the description.

Symptoms are a very hard 1-2 2-3 shifts and then faults and stays in 4th gear.

I need the trans control units pin out so I can at least make sure it's the sensor and not the control units input before I buy a new valve body.

 

[avk]

2008 FSM is different. The wiring diagram shows the rear VSS with a connector and the front vehicle speed sensor as part of the control valve body, as well as the two turbine sensors. See jpg attached.

The two versions seem to be substantially the same. There are actually two sensors mounted to the valve body on either version of the transmission, here's an example of the early type: http://legacygt.com/forums/showpost.php?p=2119276&postcount=8
Looks like I was wrong about that at least twice.

 

[plain OM]

The two versions seem to be substantially the same. There are actually two sensors mounted to the valve body on either version of the transmission, here's an example of the early type: http://legacygt.com/forums/showpost.php?p=2119276&postcount=8
Looks like I was wrong about that at least twice.

Perhaps it's just semantics.

There's only one speed sensor mounted on the valve body -- the Turbine Speed 2 sensor. This is the sensor that is being discussed in the linked post (black part with soldered connections).

The Front Vehicle Speed sensor is not mounted on the valve body; it's actually found inside the extension case area;, however, it's wiring goes to the valve body where it connects to the transmission harness. (In other words, the Front Vehicle Speed sensor wiring is all inside the transmission, unlike the rear VSS wiring, which is on the outside of the transmission.) That's why the 2008 wiring diagram shows the Front Vehicle Speed sensor outside the perimeter of the control valve body, but it's connector, T15, is in the valve body.

There wasn't a significant mechanical change in the location and wiring of the Front VSS and the Turbine Speed 2 sensor between 2006 and the 2008; rather, it's just that the wiring diagram from the earlier service manual (which you provided in post #6 above) doesn't show the Front VSS and the Turbine Speed 2 sensor in the same way as the 2008 diagram.

But, again, perhaps we just have different ways of describing the same thing.

 

[plain OM]

This is a 2008 2.5 XT

I don't recall the specific code. I didn't realize FreeSSM would dump the data when shut down. but it was no signal from Turbine 2 was the description.

Symptoms are a very hard 1-2 2-3 shifts and then faults and stays in 4th gear.

I need the trans control units pin out so I can at least make sure it's the sensor and not the control units input before I buy a new valve body.

That would probably be the P1710, which interestingly is the same problem as in the legacygt.com post that avk provided in post #11 above. (Here's the full thread link: http://legacygt.com/forums/showthread.php/installed-ipt-vb-got-cel-p0700-p0710-98446p2.html). That would be an example of someone experiencing a failed turbine 2 signal.

I've attached the FSM troubleshooting pages for the P1710.

I have to admit that I didn't realize the wires to the Turbine 2 speed sensor itself were simply soldered to the terminals of the sensor. That's a potential point of failure due to vibration. If it's the same in yours, then perhaps the wiring can be repaired, as rubberman did, and a new VB won't actually be needed.

 

[Zack66]

Thanks OM,

That what I needed.

It would be so awesome if this turns out to be a loose wire, time to drop the pan again.

 

[plain OM]

Thanks OM,

That what I needed.

It would be so awesome if this turns out to be a loose wire, time to drop the pan again.

Let us know what you find. If it turns out to be the wires, perhaps take some photos and post them here so that others reading this thread in future won't have to look elsewhere.

Also, in your first post the only symptom mentioned appears to be the absence of the sensor signal. Are there any others? Is the transmission working normally, or is malfunctioning, and if so, what is it doing?

 

[Zack66]

I finally got around to working on this some more.

I am reading a turbine 2 signal on my scope but the TCM is not registering it evidently. pin 25 plug b54.

But is only a 1.5 v+ sig :/ Shouldn't it be 5v?


http://youtu.be/9GfZZKIOB7s

 

[plain OM]

Scope signal is measured from pin 25 to ground? Test #5 in the P1710 diagnostic procedure suggests 4 - 6 V, but that's referenced to B54 pin 16, and is the constant level. So yes, the scope signal would be 5 V in overall amplitude.

Did you check the input voltage at B54 pin 27 (test #4 )? That should be near battery voltage (~12 V).

The turbine sensor has three wires; one, I believe is ground, one is supposed to be ~12 V, and the third would be the one with the sensor output square wave signal. Low voltage supply input could result in a signal too low for the TCM to make use of. A broken wire, perhaps the ground, might lead to a signal but with low amplitude.

Not much more information in the docs about what to look for and expect.

 

[Zack66]

Pin 25 to batt ground.

test 4 = 10 v but that was to a through bolt under the dash and the batt is surely low, I measured 14v on pin 27 to batt - engine running and 0 on pin 16.

test 5 =1.76v but if I disconnect the the transmission connectors it is 5v. unsure if I was supposed to reconnect after test 4.

Interestingly I read 6-14 M ohms across pins T14 1 and 4 that I traced to a sensor on the tail shaft of the trans.

I will try disconnecting the tail shaft sensor tomorrow and see what happens.

wiring harness is confirmed good as is all internal trans wiring.

 

[plain OM]

test 5 =1.76v but if I disconnect the the transmission connectors it is 5v. unsure if I was supposed to reconnect after test 4.

Yes, it's not clear, but for test 6 it says connect all, so presumably in 5 the transmission is not connected yet. The 5 V is as specified. There's no spec for the voltage on pin 6 with the tranny connected so no idea if the 1.76V is correct.

However, I'm wondering if that drop to 1.76 V could be a factor. In test 5, the 5 V must be coming from the TCM. The other two terminals are ground and the battery voltage, so this terminal must be the "signal". The sensor is probably a Hall Effect Sensor, with some circuitry built into the assembly in the transmission. When the turbine is rotating, the sensor circuit grounds the pin 6 line as the turbine magnet(s) pass the sensor. The effect is a square wave (as shown on your scope) that I would expect switches between zero and 5 V. When the transmission is connected but the engine isn't running, the Hall switching circuit should either be open (5 V on pin 6) or closed (zero on pin 6). The 1.76 V, therefore might indicate a problem in the sensor circuit that's loading the TCM input circuit. The effect is a square wave that can only go from zero to around 1.7 V (i.e. the 1.5 seen on the scope). That might be too low an amplitude (shift) for the TCM to accept as the turbine speed.

I wonder . . . with power off and the TCM disconnected (at B54 or at the B12/T3 junction), can you measure the resistance (Ohms) between T10 pin 1 and ground? This is measuring the Hall sensor output circuit. If it's low, that would explain the drop from 5 V to 1.76 V. My "Google research" on Hall effect sensors suggests that the output of the circuit, being a switch, should not have a low resistance.

This is only an attempt to explain the test measurements and the problem. Ideal would be to have the same measurements done at pin 6 for comparison. But perhaps step-by-step, we could narrow it down enough to suggest the right "corrective measure". (It might still come down to bad wiring connections at the sensor. If the wire bringing the battery voltage to the sensor at T14, pin 1, is bad, the actual voltage getting to the sensor circuit could be lower. -- more thinking on paper . . . )

Maybe we can find some data on the amplitude of the square wave signal . . .

 

[tdelker]

How is this going? Another person over on sb9t.com is having the exact same issue.

2008 Tribeca Limited /Transmission Issues - SB9T.com