5EAT in 2wd problem...........

[Seabass]

It's impossible for it to be only FWD in a 5eat. Even with the transfer clutch disengaged, the center diff will transfer power to the back.

The P1706 is a rear wheel speed sensor failure. Not a major mechanical failure. Go somewhere that will figure out the problem before charging you several thousand dollars.

[plain OM]

It's impossible for it to be only FWD in a 5eat. Even with the transfer clutch disengaged, the center diff will transfer power to the back.

I had to think about this again, and realize that with the 5EAT there are possibilities.

One is if the transfer clutch isn't kicking in when one or both front wheels loses traction. In this case, one or both front wheels can begin to spin, and as the center planetary differential is, itself, "open", the rears do nothing.

Another is a fully functioning transfer clutch, but an axle that either is pulled out from the differential or has a CV joint that is broken (inside the boot). In either case, the center differential will cause the "free" drive train (front or rear) to spin, activating the transfer clutch, which then transfers torque to the drive train that isn't free. In the first post, the problem was identified at higher speeds. It's possible that at higher speeds (and upper gears) the transfer clutch isn't as aggressively advanced (pressure-wise) as in the lower gears, and sudden throttle will cause it to slip. If an axle isn't connected, this will allow the engine rpm to increase just like a slipping clutch in a MT.

[cardoc]

Originally Posted by Seabass

It's impossible for it to be only FWD in a 5eat. Even with the transfer clutch disengaged, the center diff will transfer power to the back.

The P1706 is a rear wheel speed sensor failure. Not a major mechanical failure. Go somewhere that will figure out the problem before charging you several thousand dollars.

The AWD system on these cars is capable of many things. That's what makes them better than others.

1706 is a communication issue with the TCM to transmission. It would be beneficial to do the testing with a scan tool that reads transmission data.

I have attached a flow of diagnostics for your perusal.

[Seabass]

Originally Posted by cardoc

The AWD system on these cars is capable of many things. That's what makes them better than others.

1706 is a communication issue with the TCM to transmission. It would be beneficial to do the testing with a scan tool that reads transmission data.

I have attached a flow of diagnostics for your perusal.

It's a TCM code, but specifically a rear wheel speed sensor failure.

And it's mechanically impossible for it to be FWD. It could definitely be acting as an open center diff if the transfer clutch is disabled, which it probably is with that diagnostic code.

[AWDPete]

Thanks for the info! So far you guys have offered far more insight into what may be going on then those who want to te my money!!!!

To clarify: I can spin the front tires at will, if the rear is putting any power down I cannot be sure - however it's not normal.

The Sube dealer tested it while driving with there scan tool.

It always disengaged at 40mph, no matter what gear it was in and regardless of how aggressively the throttle was applied.

So it's sounding like one of the rear wheel speed sensor or something amiss in the rear axle?

Thanks again for the help

[plain OM]

Wait. We're sort of assuming that the loss of the rear vehicle speed sensor signal would cause the car to go into FWD, which, as has been explained, cannot happen (in otherwise normal circumstances). All that might be happening, and we're not certain about this, is that the absence of a rear speed sensor signal (P1706) might affect the way the transfer clutch reacts, but in the 5-speed AT, it's the center planetary differential that ensures both the front and rear drives are always connected to the transmission output at all times. (In effect, the clutch only serves to lock the differential, but it does not vary the connection between the transmission and the rear drive as in the 4-speed.)

You've mentioned that the fronts can be made to spin, but it appears as if the rears might not be doing anything. Questions:

When and where? Does this happen on dry, good traction pavement, or are we talking about slippery surfaces? Under what conditions can you make the fronts spin?

If you're not sure what the rears are doing, perhaps it would be better to first check this out. Have two people outside the car, to watch the wheels on both sides. Get one or both fronts to spin and see if either rear is spinning. What we need to know is if one or more fronts will spin while neither rear is turning.

What do you mean by "It always disengaged at 40mph, . . "? What's always disengaged?

I think I can make up an imaginary scenario to fit these descriptions, but I'd much rather have more details specific to the real thing.

Incidentally, from the 2005 FSM:

DTC P1706 AT VEHICLE SPEED SENSOR CIRCUIT MALFUNCTION (REAR
WHEEL)
DTC DETECTING CONDITION:
Input signal circuit of TCM is open or shorted.

[AWDPete]

Originally Posted by plain OM

You've mentioned that the fronts can be made to spin, but it appears as if the rears might not be doing anything. Questions:

When and where? Does this happen on dry, good traction pavement, or are we talking about slippery surfaces? Under what conditions can you make the fronts spin?

Dry pavement - black marks and smoke if i want too I can get one or both fronts to spin, in slush like we got today both fronts if in boost at all.

If you're not sure what the rears are doing, perhaps it would be better to first check this out. Have two people outside the car, to watch the wheels on both sides. Get one or both fronts to spin and see if either rear is spinning. What we need to know is if one or more fronts will spin while neither rear is turning.

The rears at not spinning/breaking traction at any point in time, not even in slush as far as I can tell. I will check it though.

What do you mean by "It always disengaged at 40mph, . . "? What's always disengaged?

When this first started I could not get the car to go over 40 mph, anything faster then this the motor would simply rev with no forward drive, then once the speed dropped below 40mph I could accelerate but the trans would "engage" with a "clunk". It stopped doing that now and the trans now operates "normally" with the exception that the center diff "appears" to be stuck in a 70/30 - 80/20 - 90/10 front/rear bias (don't have any idea as to actual bias) other then the rears "seem" to be doing very little to nothing.

I think I can make up an imaginary scenario to fit these descriptions, but I'd much rather have more details specific to the real thing.

Incidentally, from the 2005 FSM:

DTC P1706 AT VEHICLE SPEED SENSOR CIRCUIT MALFUNCTION (REAR
WHEEL)
DTC DETECTING CONDITION:
Input signal circuit of TCM is open or shorted.

Is there any way to find out 'which' rear wheel sensor needs to be replaced? I am assuming we are talking about the ABS sensor?

Any more questions I can answer?
Thanks again

[plain OM]

Thanks for the responses -- very helpful.

The sensor that the P1706 code is related to is the rear vehicle speed sensor. It's mounted on the transmission extension case (I think it's on the left side) and monitors the rotation of the transmission output shaft connected to the rear propeller (drive) shaft.

As far as I know, the rear speed sensor in the 5-speed can't be changed in a simple swap. The sensor and wiring harness are one unit, and this is where the cost of replacement becomes an issue. So you really want to know for sure that the sensor, or the wiring to it, is bad before taking things apart.

If you can get the fronts to "burn rubber" on dry pavement while the rears (both) just roll along for the ride (presumably from a standing start), I'd say either the AWD clutch isn't working as it should or there's a broken coupling/CV joint in the rear drive train, as I mentioned in post 22 above.

That said, the defective/missing signal from the rear vehicle speed sensor (P1706), if it is current, could very well be the root cause. Without any signal for the rear drive, the TCM can't determine if the rear drive and the front drive are turning at the same speed or not. The whole idea of the differential and multi-plate clutch is to ensure that they are (at least whenever a wheel loses, or can lose, traction).

What is surprising, however, is that you don't report any warning lights -- I would expect either the AT Oil Temp light, or the "Sport" light, and perhaps the CEL to be on when they shouldn't be, if a current trouble code is set.

We don't know what the dealer did to identify the code, and especially if it was cleared, the car driven, and found to reappear (meaning it is "current" and not just an old, saved code).

Over in this thread we have used two free programs that can monitor the transmission control unit's signal to the transfer clutch. Seabass used them with a 2005 XT, confirming their compatiblity with that transmission. In the thread the question of how the transfer clutch control signal, and therefore the clutch, is varied is examined as part of our test of what the programs can reveal. (The thread is long, but might be worth reading through.)

With something like RomRaider Logger hooked up, the presence or absence of rear wheel speed signal can be verified, and the variation in clutch control pressure (5EAT reads out in psi) can be seen when, for example, the front wheels break loose. (All this can be logged and examined later in a spreadsheet). This would help identify if there's a missing rear wheel speed signal, and if the clutch engagement isn't being advanced when it should be. (Seebass reports some figures in post #39 and elsewhere.)

If when the fronts break loose, the clutch pressure is increased, yet the front and rear speeds aren't brought into sync, then I would say there's a mechanical "disconnect" somewhere in the rear drive train.

Narrowing it down, I think . . . .

[Seabass]

You can read input from the rear wheel speed sensor with either of those programs. I'm hoping that the sensor has failed and the transfer clutch is disabled causing it to act as an opened diff, but the front wheel burn outs plus rears not spinning in the snow points to something mechanical. Especially in slush from a standstill, you have more weight in the front plus a slight rear torque bias. If your center diff is open from no transfer clutch, the rear should break loose and spin, not the front.

I'm also very concerned about not being able to go over 40mph. Even in limp mode, you can drive at highway speeds, just not over 4k rpm. A VSS failure could put the car into limp mode. Although, if you give it too much throttle in D or Sport, it will downshift and put you past the limp mode rev limit fuel cut. Any chance that was happening?

[Primotenente]

Originally Posted by plain OM

(...) there's a broken coupling/CV joint in the rear drive train, as I mentioned in post 22 above.(...)

This would also be my guess. It seems to be something mechanical.

The rear axle is not driven and the clutch locks due to the "freeweehling" rear axle. As soon as the car gets faster, the clutch partially re-opens, because you do not need/want a diff-lock at higher speeds. The partially unlocked clutch gives him that feeling something is "slipping".

I am pretty shure, freessm will show the decreased pressure on the clutch once he goes faster than 40 mph.