Diagnosing crow-hopping on a AWD 9-7x

JoeSaab

Silver Supporter
Bottom line- Trying to diagnose a crow-hopping condition on a '06 SAAB 9-7x. 195K miles.


I have a 9-7X that appears to be running well EXCEPT for crow-hopping. No OBD2 codes with a scanner and no codes using a Tech2 (makes me feel its purely mechanical that the sensors don't see). I've been replacing parts based on the prior owner's mechanic recommendations- big parts! The vehicle is new to me and I purchased with the known issue, so my history with knowledge of the vehicle is limited. The prior owner had it towed to two mechanics and both diagnosed it as a bad transfer case, but mechanic estimate to replace the transfer case was more than the prior owner could afford (>$2500).

Here's what I have done. I've replaced the transfer case with a "known good" used part. No noticeable change whatsoever. After the transfer case swap made no change, I changed the rear diff fluid and found black goo inside and some small chips of metal. Thinking the rear differential is toast, I replaced the read diff (G86 limited slip) with a "known good" used part (with only 30K miles!). Again, no change whatsoever to vehicle performance. In both instances I replaced the fluid with appropriate GM fluid.

I understand the risks with replacing with used parts. Statistically, I should have seen some sort of change if the parts I installed are better -or worse.

I then replaced the fluid in the front diff. It was significantly low and the old fluid had very fine metal shavings- hard to tell if significant enough to call it bad, but more than I expected. Of course, hindsight is 20/20 and I should have checked/changed this fluid level earlier, but the prior owner swore it was maintained perfectly.

I am hoping for a way to isolate the problem. Reading many many posts I have come up with several ideas to help troubleshoot. One idea is to pull the encoder motor to see of the front drive is responsible for the problems. Alternatively, can I remove the front driveshaft and test it as a 2wd? What is the likelihood of the CV axles contributing to the crow-hopping by binding? (grasping at straws here). What is the impact of the encoder motor removed and/or front drive shaft?

Thanks in advance for an sage advice.

Joe
 

Mooseman

Master Blaster
Moderator

When the transfer case was replaced, was the encoder motor also replaced with it or did you keep the one from your original case? Try removing the motor. It should shift out of AWD naturally.

The front diff could also be responsible if it's totally shot and has locked both wheels together as if the spider gears were welded. If you jack up the front end, turning one wheel should either make the other wheel turn in the opposite direction or turn the driveshaft. If the driveshaft is held in place, it should then turn the other wheel in the opposite direction.
 

TequilaWarrior

Active Member
How did you arrive at "known good" for the t-case?
Crow-hop is a known issue with AWD GMT360s when the fluid is not maintained properly. I suspect if the T-Case was pulled and not stored correctly it could end up in a similar condition.

Typically, the crow-hop fix (simplest) is 2 consecutive T-Case fluid changes with only fresh, pure, Auto-Trak II. Change fluid, drive... (500? miles).... change again.... That's what cured my crow-hop.

Did you verify the function of the T-Case before installing it? Did the front output shaft spin independently of the rear output shaft when the encoder was disengaged?
If you did - and it does - pull the encoder motor. If you still have crow-hop it virtually guarantees it's the front diff.
 

JoeSaab

Silver Supporter
Thread Starter
Thank you for the quick replies. “Known good” transfer case and encoder just means I purchased used with a warranty. I really did not verify operation. The used transfer case came with an encoder, so I performed a complete swap of all components.
I believe my best plan, based on advice, is to Physically pull the encoder out and see if The problem disappears. I also will drain & fill the transfer case (Again) with Trak II. After that, raise the front wheels and verify front differential operation.

Thanks for helping with the battle plan. Much appreciated. Being unfamiliar with the GMT platform has been frustrating, so this is quite helpful.
 
Thank you for the quick replies. “Known good” transfer case and encoder just means I purchased used with a warranty. I really did not verify operation. The used transfer case came with an encoder, so I performed a complete swap of all components.
I believe my best plan, based on advice, is to Physically pull the encoder out and see if The problem disappears. I also will drain & fill the transfer case (Again) with Trak II. After that, raise the front wheels and verify front differential operation.

Thanks for helping with the battle plan. Much appreciated. Being unfamiliar with the GMT platform has been frustrating, so this is quite helpful.


Being the curious fellow I am (interpretation left to the reader) I would want to monitor the range position sensor return signal.

From the wiring diagrams it appears to use the same controller? I would expect the operating software/calibration to be different for an AWD system though.

At any rate, if my current custom setup in Torque Pro didn't get at the value I would likely rig up a wire that tapped into the return signal at the TCCM so I could see that voltage. That would indicate how much apply pressure is applied to the front propshaft clutch.

If I were to assume the encoder motor and internal range position sensor are the same as the A4WD system then I would already have a fairly good handle on hiw much apply pressure was currently in force.


More random musings from a guy with too much time on his hands.
 

Chickenhawk

Hobbyist
It might be as simple as a broken wire to a wheel speed sensor There is a TSB on that.

The vehicle senses a difference in speed and locks up the transfer case. The TSB mentions a broken wire at the sensor itself, but mine was deep underneath the fuse block where a tiny probe had created a moisture entry point.

I am not an expert on the AWD so I can't steer you toward which wires to check at the TCCM.
 

JoeSaab

Silver Supporter
Thread Starter
UPDATE: Removing the transfer case encoder motor definitely eliminated the crow-hop. I also did raise the front end off the ground and turned the passenger and driver front wheels one at a time. This test was after i removed the encoder so there was nothing (naturally) holding the front driveshaft in place. When I turned either wheel, only the drive shaft turned- the other wheel stayed put. I'm assuming this means the differential is not seized, correct? Or should I redo this test holding the driveshaft from turning?

Is there any additional test (aside from buying a replacement encoder motor) to diagnose the problem? I'm not familiar with the inner workings of the AWD wiring to tap signals, but I take direction well. Also, is there some way to tell when AWD engages so I can eliminate the possibility of a bad sensor wire (as suggested by ChickenHawk?)
 
EDIT: I looked at a Rainier owners manual and I think the Saab has the same drivetrain. If so then you do not have a transfer case neutral position and the rest of this post is moot.





Removing the transfer case encoder motor definitely eliminated the crow-hop

One possible caution will I state. If the transfer case is the same as the selectable 4WD system I don't think there is a detent that stops the transfer case from slipping out of 2Hi and into the transfer case neutral position. If that happens then there is no longer anything stopping the truck from simply rolling away, even in Park! For the selectable 4WD systems it is an electric brake in the encoder motor that holds the range selection in place. AGAIN, I DO NOT know if the transfer case and encoder motors are the same for an AWD system.
 
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Mooseman

Master Blaster
Moderator
The AWD transfer case has only two positions; 2wd and AWD, which is essentially the same as 4hi. It doesn't have an internal brake nor does the encoder motor to hold it in a position, unlike the 4x4 system. When the AWD engages due to rear wheel slippage, it will engage the front wheels and then slowly disengage and return to 2wd.

I'll bet that with both transfer cases it was the encoder motor that was defective. It's a very common failure. Same thing happened to me in the Saab, replaced the encoder motor and it was back in order.
 

TollKeeper

Gold Supporter
Couple minor questions.
Do you have any ABS lights on the dash?
Have you verified that each wheel speed sensor is reporting the same speed to the system?

It could be the encoder motor, but it could be the system engaging the encoder motor from bad info from other parts of the system.
 
could be the encoder motor, but it could be the system engaging the encoder motor from bad info from other parts of the system.

This is what led me to suggest monitoring the encoder motor position through the only part capable of reporting the position of the encoder motor and transfer case, that is the range position sensor inside the encoder motor.
 

Mooseman

Master Blaster
Moderator
Just in case it's needed, here's the schematics:
 

Attachments

  • A4WD_Schematic.pdf
    160 KB · Views: 5
And as it turns out that as far as the encoder sensor goes the connections at the TCCM are precisely the same as the range position sensor for the selecatble 4WD system.

Just ignore the references to a dashboard control switch in this image...

IMG_20200422_175022.jpg
 

JoeSaab

Silver Supporter
Thread Starter
Couple minor questions.
Do you have any ABS lights on the dash?
Have you verified that each wheel speed sensor is reporting the same speed to the system?

It could be the encoder motor, but it could be the system engaging the encoder motor from bad info from other parts of the system.
No ABs lights. No error codes whatsoever. (with the encoder pulled I have the drivetrain service icon) I'm looking at how I can read speed sensor values... need to find the decode for the encoder motor. (is it on/off for power to the front wheels at C1/B6?)

Pardon my ignorance. Learning about the platform. :smile:
 

TollKeeper

Gold Supporter
No ABs lights. No error codes whatsoever. (with the encoder pulled I have the drivetrain service icon) I'm looking at how I can read speed sensor values... need to find the decode for the encoder motor. (is it on/off for power to the front wheels at C1/B6?)

Pardon my ignorance. Learning about the platform. :smile:
You will get no guff from me!

I have a hard enough time remembering these have more than 1 engine! Quite a few times @MRRSM and @Mooseman have had to come in behind me and correct me. I am a lot more familiar with the V8 models. But I am learning!
 
I'm looking at how I can read speed sensor values... need to find the decode for the encoder motor. (is it on/off for power to the front wheels at C1/B6?)

Not a fixed value like on or off but a varying voltage. The TCCM supplies the sensor with a 5 volt signal and a 'low reference' (ground). Depending on where the shift motor is at it sends back a voltage somewhere between like . 5 volts up to maybe 4.5 volts. I don't know what the range is for the AWD system as I have only worked on the selectable system.
 
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Here in this video I am reading the encoder motor position sensor for the selectable 4WD system. As far as the sensor goes it should be similar except that you don't have a switch or the 4 fixed positions the selectable system has. What I would expect to see would be a fairly steady voltage, taking a wild guess it might be from say 3.1.volts up to 3.9 volts. And further guessing would say the more clutch apply pressure is commanded the higher the voltage would read.

EDIT: having taken a quick look at the nvg 126C internals the voltage could also very well go the other way, and in a different range than my first guess.


 
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JoeSaab

Silver Supporter
Thread Starter
Good morning, and thanks for all the information and ideas so far. To summarize this thread so far, to help diagnose a crow-hop condition (at least for this condition and my situation),
1. Ensure (and likely drain/fill) the transfer case with GM Auto-Trak II fluid). Twice in 500 miles appears as the recommended course of action in this case.
2. Disconnect and remove the transfer case motor to split the drivetrain (front/rear) and assess if the crow-hop is removed. if crow-hop remains, it is likely attributed to the rear end components. If crow-hop is gone, the front diff, axles, transfer case motor , or sensors likely at fault (transfer case is the common fault). Further testing by monitoring the traction case control module (TCCM) to verify that operation is normally in 2Hi and not AWD continuously.
3. Raise front end and test front diff to see if diff gears are not locked. Drain/fill as necessary. (Always good to drain/fill front& read diff)
4. To test what position the position of the transfer case motor (re-install transfer case motor if previously removed) and monitor TCCM (location @ front passenger panel) pins for proper signal. Connector 1 (C1)/B6 to C1/A7 appear as the pins I need to monitor. (still researching this test and expected voltages).
 

Mooseman

Master Blaster
Moderator
2. Disconnect and remove the transfer case motor to split the drivetrain (front/rear) and assess if the crow-hop is removed. if crow-hop remains, it is likely attributed to the rear end components. If crow-hop is gone, the front diff, axles, transfer case motor , or sensors likely at fault (transfer case is the common fault). Further testing by monitoring the traction case control module (TCCM) to verify that operation is normally in 2Hi and not AWD continuously.
"if crow-hop remains, it is likely attributed to the rear end components." : Not necessarily. If the front diff has both wheel locked to each other and both turning in the same direction, then that would be a diff failure as it's supposed to be an open diff.

The rear diff is a G86 limited slip and is not likely to fail like the G80 locker on the 4x4 trucks. Usual failure is of the wearing out of the clutches and it would not transfer power to the wheel with more traction. Only exception would be if LS additive was not added to the rear diff oil. That would cause rear end tire squeal in corners and some rear crow hop on hard tight turns.

If you remove the encoder motor and the hop stops, then it's basically an issue at the encoder motor level where the transfer case returned to its natural 2wd position. One way you could test the motor is to jack and use jack stands at all four corners to get the tires off the ground, plug in the encoder motor but don't install it on the transfer case, start the engine and put it in drive. While only the rear wheels are turning, the TCCM will try to engage the encoder motor. Check if you see the gear move. Try to move it with a tool in the opposite direction. You can also turn the spindle (clockwise IIRC) on the transfer case with pliers to engage the front wheels and see if that's working correctly.
 

TequilaWarrior

Active Member
2. Disconnect and remove the transfer case motor to split the drivetrain (front/rear) and assess if the crow-hop is removed. if crow-hop remains, it is likely attributed to the rear end components. If crow-hop is gone, the front diff, axles, transfer case motor , or sensors likely at fault (transfer case is the common fault). Further testing by monitoring the traction case control module (TCCM) to verify that operation is normally in 2Hi and not AWD continuously.

The logic here is flawed. Removing the tc motor removes the force causing the clutches to engage if and only if the encoder motor is stuck (commanded or otherwise) at engagement. If crow-hop remains, your TC clutches could be stuck - the fluid change should unstick them if poor maintenance was the cause, but that's not necessarily 100% guaranteed - it could be stuck for other reasons although this possibility is remote if you've done the fluid change. If crow-hop remains it could alternatively be a FRONT diff failure. Crow hop doesn't really happen due to anything from the rear diff. TRUE crow-hop is the result of the two front wheels attempting to turn at different rates while locked together. I've run locked rears in several vehicles and have had seized lockers. It negatively affects your turning radius and presents as binding, but not as badly as front-diff engaged "crow-hop". With a locked (seized) rear, the REAR tires will "chirp" in a turn, not the front.
If crow-hop is cured by removing the tc motor - this is more informative than it remaining - it narrows it down to the TC motor itself, or the controls commanding it to engage, which could be cause by a sensor fault, TCCM fault, wiring (to wheel speed sensors, to/from TCCM, etc...).
 

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