Rare problem: 5th/6th gear bucking/surging and cruise control not working

[arsenalrocks]

this is a problem that the dealer is unable to figure out after multiple tries.

once the car is warmed up, after 10 mins of highway driving between 65mph to 75mph, only in 5th or 6th gear, the car will feel slight jerkiness (as if someone is modulating the clutch on/off) then wrench sign comes on, at full stop then "hill start assist not available".

this issue started happening at the 3rd year of the ownership, no issues on 4th gear and below, only 5th and 6th, more frequent on 5th than 6th. and it doesn't happen at colder temps, only when everything is warmed up and only happens at constant highway speeds.

been tracking the car often, but on track i don't use 5th. changes my ATF yearly so it is mostly clean, no signs of metal when changing ATF.

Dealer replaced the clutch sensor, didn't help one bit.

any ideas of what could be the issue? this is super rare.
car is 16 GT350 tech pack no cooler on transmission.

Thanks

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[JAJ]

I think you're looking in the wrong place for the problem. Hill start assist is an ABS function, and the "unavailable" message originates in the ABS module. It sounds like the ABS module is sensing a problem and cycling the brakes to produce the jerkiness and then going into an error state that disables hill start. It might disable other stuff too.

I'd start by checking the wheel speed sensors to see if they're covered with gunk.

 

[arsenalrocks]

thank you, will check all those, worst comes to worst, replace all 4 sensors.

I think you're looking in the wrong place for the problem. Hill start assist is an ABS function, and the "unavailable" message originates in the ABS module. It sounds like the ABS module is sensing a problem and cycling the brakes to produce the jerkiness and then going into an error state that disables hill start. It might disable other stuff too.

I'd start by checking the wheel speed sensors to see if they're covered with gunk.

 

[Shift]

thank you, will check all those, worst comes to worst, replace all 4 sensors.

Good luck on finding out the problem. Love your signature.

 

[w3rkn]

I am a little concerned that your Dealer didn't know that "hill assist" is a brake/ABS issue.

 

[TDC]

arsenalrocks good chance the issue is the trans tail shaft sensor. There is a TSB on it. Check to see if your cruise control doesn’t work or intermittently works when experiencing the 5th/6th gear issue.

For me after a 10-20 minute warm up and some fairly heavy throttle applications there was a VERY brief power interruption only in 5th and 6th gears along with an intermittent cruise control function and wrench light. The code was for the clutch switches but had nothing to do with it. It was fixed under warranty.

 

[arsenalrocks]

on the later visit they also performed TSB 18-2322, which is to replace four bolts on the drive shaft or something. I have actually never used cruise control.
also on the first visit they did replace the clutch switch sensor, that made no difference.

do you happen to have the TSB number?

in any case I will first clean the wheel speed sensors first and see if that helps.

arsenalrocks good chance the issue is the trans tail shaft sensor. There is a TSB on it. Check to see if your cruise control doesn’t work or intermittently works when experiencing the 5th/6th gear issue.

For me after a 10-20 minute warm up and some fairly heavy throttle applications there was a VERY brief power interruption only in 5th and 6th gears along with an intermittent cruise control function and wrench light. The code was for the clutch switches but had nothing to do with it. It was fixed under warranty.

 

[TDC]

on the later visit they also performed TSB 18-2322, which is to replace four bolts on the drive shaft or something. I have actually never used cruise control.
also on the first visit they did replace the clutch switch sensor, that made no difference.

do you happen to have the TSB number?

in any case I will first clean the wheel speed sensors first and see if that helps.

TSB 19-2090 info is here:
https://www.mustang6g.com/forums/threads/tsb-19-2090-surge-or-hesitation-with-no-dtcs.119387/

Looks similar to TSB 18-2322 but with more up to date info. Did they actually replace the sensor or did they just fiddle with the bolts?

The symptoms are almost a dead on match with my car with the exception of hill assist fault. Maybe they didn’t execute the corrective action properly for the TSB.

At the 1:45 mark in the video below you can hear the power interruption in 5th gear

 

[arsenalrocks]

Thank you very much for the link.
I checked my invoice TSB 18-2322 against the newer TSB 19-2090, the items replaced are exactly the same.
Then i realized the only difference between 18-2322 and 19-2090 is the inclusion of newer model year cars such as 2019 so looks like this issue affects newer cars as well.

FYI they did not replace any sensors at all for TSB 18-2322, only the bolts and nuts per the TSB.

this issue was very annoying for them as well b/c it is very intermittent. During test drive the dealer is unable to reproduce the issue. sometimes it happens after 10 mins, sometimes 20, 30 mins. funny thing is it never happens at cold temp or start up and only at highway speeds or above. and 0 issues on track using 4th gear and below.

do you happen to have the part # for "trans tail shaft sensor", I am trying to find the part on the parts site but no luck so far.

per your suggestion I am also going to test out the cruise control function.

TSB 19-2090 info is here:
https://www.mustang6g.com/forums/threads/tsb-19-2090-surge-or-hesitation-with-no-dtcs.119387/

Looks similar to TSB 18-2322 but with more up to date info. Did they actually replace the sensor or did they just fiddle with the bolts?

The symptoms are almost a dead on match with my car with the exception of hill assist fault. Maybe they didn’t execute the corrective action properly for the TSB.

At the 1:45 mark in the video below you can hear the power interruption in 5th gear

 

[TDC]

Thank you very much for the link.
I checked my invoice TSB 18-2322 against the newer TSB 19-2090, the items replaced are exactly the same.
Then i realized the only difference between 18-2322 and 19-2090 is the inclusion of newer model year cars such as 2019 so looks like this issue affects newer cars as well.

FYI they did not replace any sensors at all for TSB 18-2322, only the bolts and nuts per the TSB.

this issue was very annoying for them as well b/c it is very intermittent. During test drive the dealer is unable to reproduce the issue. sometimes it happens after 10 mins, sometimes 20, 30 mins. funny thing is it never happens at cold temp or start up and only at highway speeds or above. and 0 issues on track using 4th gear and below.

do you happen to have the part # for "trans tail shaft sensor", I am trying to find the part on the parts site but no luck so far.

per your suggestion I am also going to test out the cruise control function.

I’ll have to find where I put the paperwork. At first the dealer couldn’t replicate the issue on my car but then I drove the tech around and after about 10 min and heavy throttle application then I could always get it to repeat in 5th and 6th

 

[526 HRSE]

Thank you very much for the link.
I checked my invoice TSB 18-2322 against the newer TSB 19-2090, the items replaced are exactly the same.
Then i realized the only difference between 18-2322 and 19-2090 is the inclusion of newer model year cars such as 2019 so looks like this issue affects newer cars as well.

FYI they did not replace any sensors at all for TSB 18-2322, only the bolts and nuts per the TSB.

this issue was very annoying for them as well b/c it is very intermittent. During test drive the dealer is unable to reproduce the issue. sometimes it happens after 10 mins, sometimes 20, 30 mins. funny thing is it never happens at cold temp or start up and only at highway speeds or above. and 0 issues on track using 4th gear and below.

do you happen to have the part # for "trans tail shaft sensor", I am trying to find the part on the parts site but no luck so far.

per your suggestion I am also going to test out the cruise control function.

Did you ever figure out what this was? Same thing happened to me today.

 

[526 HRSE]

I shut off hill assist and the dashboard wrench went away. Still feel the intermittent stutter, though.

Not sure if it's related, but i just noticed my A/C compressor wasn't coming on.

 

[arsenalrocks]

nope, car is currently in the shop, they replaced the "trigger wheel sensor" and re-torqued some fringe nuts, the "jerk" is much much less now but wrench light still comes on

for most people tho, the TSB 19-2090 fixed the issue.

As TDC said, the easiest way is to check if your cruise control is working, if it is not then the issue is not fixed.

Did you ever figure out what this was? Same thing happened to me today.

 

[526 HRSE]

Was yours doing the same thing his was doing in the video? Mine does it at steady rpm's, but it's much less noticeable. Acts like a dirty fuel line or misfire. 3k in 5th gear is where i notice it most. I rarely go into 6th.

I just checked the relay and fuse for the A/C. Started car and now i have a check engine light...

 

[arsenalrocks]

Mine is similar to yours, ONLY at highway cruising constant speeds, 5th year around 3k sounds exactly right. happens in 6th gear as well. never an issue on 1-4th.

the first thing i would recommend is to get TSB 19-2090 done at your dealer, ask them to check specifically for "trigger wheel sensor" wear condition, replace if needed

Was yours doing the same thing his was doing in the video? Mine does it at steady rpm's, but it's much less noticeable. Acts like a dirty fuel line or misfire. 3k in 5th gear is where i notice it most. I rarely go into 6th.

I just checked the relay and fuse for the A/C. Started car and now i have a check engine light...

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