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Discussion Starter · #1 ·

I took my Ascent (21k miles, 5/2018 build date, 12/2018 purchase date) into the dealer last month for wildly surging RPMs on hills on the highway, rough "shifts" under moderate acceleration (vibration / feels like driving over a garden hose), and lurching "shifts" under light acceleration (feels like bad manual clutch technique).

They found something on day 1, kept it for 6 days, then backpedaled and said there is nothing wrong. I took this video on the way home -- it still feels very wrong to me.

The new recall is very short on details, but I'm thinking that "CVT chain slip" sounds very much like what I'm seeing. Thoughts?
 

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That seems like improper ratio regulation, and doesn't look or sound like chain slip issues.

Regardless, it's definitely not right.

It may be resolveable with a TCM reprogram or may need parts, but that's something the dealership would need to diagnose. That takes a bunch of specialized tools I don't have, and can't use remotely. ??

Sorry, too much coffee.

Seriously though, I'd bring the vids and have your service center check it out.
 

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Discussion Starter · #4 ·
Thanks Robert,

Normally I'd agree about "have your service center check it out" but given that they just worked on it for 6 days (bringing the total to 17 days in the shop for 2019) and said nothing's wrong, I'm not sure where to go.
 

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Thanks Robert,

Normally I'd agree about "have your service center check it out" but given that they just worked on it for 6 days (bringing the total to 17 days in the shop for 2019) and said nothing's wrong, I'm not sure where to go.
Please email Subaru of America and send them links to the videos.

Alternatively, you can bring your car in for the recall and see if the Transmission Control Module software update resolves it.
 

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At the lest it need the TSB done for belt slip. I bet you get a new trans
Possibly, but generally, such things have been fixed with a TCM software update. There's no screeching or chain slipping. It up shifts, down shifts and repeats over and over. It's consistent in each shift point.

I am interested to hear what the final solution is.

As for the "rough" shifting, the TCM update resolves that.
 

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Discussion Starter · #8 ·
Robert, is this what you mean by screeching / chain slipping?

I'm still waiting for another dealer service appointment, but things took a dramatic turn for the worse today. Lost power going up a hill at 55 mph on the highway, then the christmas tree lights came on. I limped home with heavy vibration after each shift, with frequent surges and squealing. I managed to record this at a quiet spot as I was nearing home...

Currently arranging for a tow...
 

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Robert, is this what you mean by screeching / chain slipping?

I'm still waiting for another dealer service appointment, but things took a dramatic turn for the worse today. Lost power going up a hill at 55 mph on the highway, then the christmas tree lights came on. I limped home with heavy vibration after each shift, with frequent surges and squealing. I managed to record this at a quiet spot as I was nearing home...

Currently arranging for a tow...
Sadly, yes. You will be receiving a new CVT and a new harness.
 

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Sadly is one way to look at it. To try to put a positive spin on it, you'll be getting a definitive fix for the CVT issue, namely a new harness and transmission. I'm still not yet totally convinced that the WUV07 process and TCU update can conclusively detect a problematic harness and that it's not something that could fail down the road.
 

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If you read this NHTSA report regarding this recall, it will make everything clearer. The TCU update is there to compensate for the increased electrical resistance in the V1 harnesses; it doesn't detect them, just works around them (ie. relax the thresholds).

"Description of the Cause" and "Chronology" sections are an interesting read. Apparently, they first heard of this problem from Canadian market.

https://static.nhtsa.gov/odi/rcl/2019/RCLRPT-19V855-2068.PDF
 

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If you read this NHTSA report regarding this recall, it will make everything clearer. The TCU update is there to compensate for the increased electrical resistance in the V1 harnesses; it doesn't detect them, just works around them (ie. relax the thresholds).

"Description of the Cause" and "Chronology" sections are an interesting read. Apparently, they first heard of this problem from Canadian market.

https://static.nhtsa.gov/odi/rcl/2019/RCLRPT-19V855-2068.PDF
Thank you! First hand technical information! So, dissimilar metals used in the contacts cause an oxide film to form, this obviously cannot be stopped with an update. However, if the sensor was sending an analog signal, the TCU can compensate by keeping a higher safety margin on the clamp force. But... still not being able to know if the pressure is real or not, or how thick that oxide film will become over time makes me think eventually all harnesses will fail. I guess in a couple of years, the film will be so thick we'll need another TCU update to increase the safety margin even more. Unless the chemical reaction reaches an equilibrium somewhere and the film does not become thicker over time. If that's the case this TCU update might work long term. Time will tell, I hope not too much time or we will be all out of warranty...
 

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Thank you! First hand technical information! So, dissimilar metals used in the contacts cause an oxide film to form, this obviously cannot be stopped with an update. However, if the sensor was sending an analog signal, the TCU can compensate by keeping a higher safety margin on the clamp force. But... still not being able to know if the pressure is real or not, or how thick that oxide film will become over time makes me think eventually all harnesses will fail. I guess in a couple of years, the film will be so thick we'll need another TCU update to increase the safety margin even more. Unless the chemical reaction reaches an equilibrium somewhere and the film does not become thicker over time. If that's the case this TCU update might work long term. Time will tell, I hope not too much time or we will be all out of warranty...
In that report, they also say that after the TCU is updated, a test drive is done and if certain DTCs show up then they'll replace the harness with the new version (if no codes, then you keep your current harness). So I think that should take care of those borderline harnesses that have too high of electrical resistance for even the new TCU firmware to work properly. That probably (hopefully) means this TCU update will do some error checking and purposely throw out those codes if it didn't like the harness or something like that. That would take care of future problem with the harness too, assuming these DTCs show up as CEL to warn the owner.
 

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If you read this NHTSA report regarding this recall, it will make everything clearer...

https://static.nhtsa.gov/odi/rcl/2019/RCLRPT-19V855-2068.PDF
Totally awesome. This clears up all the speculation and goes a heck of a lot farther describing the problem as a "bad harness". It also states that the harness can deteriorate with time, which was something I wondered about. The TCM update description seems to me to be a whitewash. Your harness may still develop the problem and become defective, but the reprogram will work around it. (essential not act on what it suspects is an erroneous pressure indication based on other parameters). If it does this, detects the issue while preventing damage to the transmission, and throws an error, that could be a good thing, though not as good as having a good harness in the first place.

This is certainly way less expensive for Subaru than replacing all potentially defective harnesses.
 

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I schedule repair three weeks ago due to chains slip at around 20mph and 40mph... they did the two recalls yesterday WUV-07 (chain slip) and WUU-06 (ECU programming). After repairs still slips and actually worse. Now slips at 55mph. I just had tech hook up computer and we drove around logging each time car slipped. He on phone with corporate to authorize repair most likely transmission! Luckily I didn’t have the PCV recall. Read the info about that. If they can’t find broken pieces they will have to replace the Engine!
 

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Discussion Starter · #17 ·
Thanks to all who have replied here. Just a quick update... I had it towed to the dealer, and re-engaged Subaru of America. The dealer promptly got the car on the lift, but 7 days later, there is still have no diagnosis -- just an open SOA Tech Line case. I will post another update when I know more.
 

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Thanks to all who have replied here. Just a quick update... I had it towed to the dealer, and re-engaged Subaru of America. The dealer promptly got the car on the lift, but 7 days later, there is still have no diagnosis -- just an open SOA Tech Line case. I will post another update when I know more.
The diagnosis is that the chain is slipping. The CVT needs to be replaced, with the harness. Period. I am so sorry that they are not able to address this adequately. Please make sure you stay in touch with Subaru of America, and message me which dealership can't figure this out.
 

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How long did the repair take on the CVT chain? A bit late to ask but the dealer could not tell me or call back to inform me.
My car goes in today for the CVT chain issue.
Another issue I see in the video and it may not be a problem at all. The Ascent has an 8 speed transmission and what you are seeing may simply be the transmission changing gears.
 

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How long did the repair take on the CVT chain? A bit late to ask but the dealer could not tell me or call back to inform me.
My car goes in today for the CVT chain issue.
It's a harness issue. It takes under an hour to test the car and reprogram the TCU, from when they take the car in.

In the event they find a bad harness, or a CVT damaged by the harness, it will take longer (6ish hours if they have the CVT or harness in stock).


Another issue I see in the video and it may not be a problem at all. The Ascent has an 8 speed transmission and what you are seeing may simply be the transmission changing gears.
The Ascent does not have an 8 speed transmission. There are no drive ratio gears.
 
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