Dealer found problem. Here is their description:
'2505 diagnosed tap shift concern, no codes, no bulletins, no diagnostics in SI for tap shift inop, test drove found car would shift in and out of manual to auto and down shift to first gear on it's own. Took a snap shot of trans data, found driver request showed down shift and invalid, tested circuits at steering wheel tap shift switches circuit #`375 and 1996. Found circuits good, removed center console to gain access to shifter and connector X202, tested circuits #5526 and 1375, found eratic ohms readings. Called TAC case #71-1175477338; determined the micro switch internal to shifter is no good, replaced shifter and rechecked, found working as designed.'
Internal Module Failure:
8460670 Transmission Control Replacement
136 WM4
FC: Part#: 25824054
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Here is what we went through to get it diagnosed. Intermittent short (I believe on reflection it would only recreate on wet days).
April 30, 2013
John Enkler, Service Manager
Hudson Cadillac Buick GMC
2023 South Road
Poughkeepsie, NY 12601
Re: Description of Transmission Problem Experienced
on our new 2013 CTS-v, delivery taken April 1, 2013 VIN# 2GKFLTEKXC6341032
Dear Mr. Enkler,
As provided on April 18th, 2013, when we recreated the problem at the dealership, here are the symptoms we have observed of the intermittent transmission problem on our new CTS-v.
When in manual sport transmission mode:
• Suddenly, the transmission spontaneously starts downshifting all the way down to 1st gear even though the RPMs were already high enough and the driver was not pushing down on the accelerator pedal. The driver shifted back to automatic mode as quickly as possible so as not to hurt the engine.
Once in this mode, the driver went to a parking lot to experiment under more controlled conditions. After a few iterations of the problem described above, a couple different symptoms emerged after switching in and out of automatic again once the problem was extant:
• In one case, the display no longer indicated ‘M’ (manual) mode, even though the driver was shifting with the shift lever. All requests by the driver to shift are ignored.
• In another case, shifting up and down appeared reversed, ie a driver request to manually shift down didn’t do anything, a driver request to manually shift up caused the transmission to actually shift down. Note: is it possible that this is what the car is doing when it spontaneously heads to first, ie does it think it’s shifting up in order to avoid too high RPMs, when it’s actually shifting down?
• In another case, while stopped, the car continuously switched back and forth between manual and drive as indicated by the display (switching back and forth approximately every 2 seconds, ie about a second per switch). While this was occurring, the driver was not touching either the paddles or the stick shift.
The problem does not reliably re-create but it has re-occurred a number of times since we first got the car. Perhaps it is temperature related (it does seem more likely to occur after it’s been driven for some time)? Also, is it possible the car thinks it’s stopped when this occurs since it automatically goes to 1st gear in ‘M’ (Manual) mode by plan once stopped?
We appreciate your attention in getting a fix for this problem as soon as possible as we are not comfortable driving the car in anything other than automatic mode until this is fixed. We are also concerned about possible engine and drivetrain damage due to unusual stress outside of normal design parameters.
June 19, 2013
John Enkler, Service Manager
Hudson Cadillac Buick GMC
2023 South Road
Poughkeepsie, NY 12601
Re: Continuing Description of Transmission Problem Experienced
on our new 2013 CTS-v, delivery taken April 1, 2013 VIN# 2GKFLTEKXC6341032
Dear Mr. Enkler,
Here are some additional notes and observations on our continuing intermittent transmission problem on our CTS-v since April 30th, when you were unable to diagnose the problem.
• During early May, we tried to reproduce the problem a number of times, but were only able to do so when your repair facility was not available, including while on a trip home from PA on May 23rd. In these instances, the problem did not reproduce after the first instance.
• On June 1st, a Saturday afternoon, the problem reproduced a number of times on the same trip, but stopped doing so after sitting (overnight).
• On June 8th, a Saturday morning, the problem reproduced a number of times even after turning off the ignition for over 20 minutes, twice. At this point, we talked to Dave in service, who told us there was no transmission tech in and to bring the car in on Monday.
In the last case, the circumstances were as follows.
• Was cruising without acceleration in 3rd or 4th gear and went into sport mode. Then, it either continued to shift down through the gears towards first or the manual gear number light blinked on and off continually. Sometimes, at this point, the gear number display would stay off at which time the car would no longer go in sports mode despite moving the shifter to ‘M’ or trying to shift with the paddles.
We do not consider it reasonable that we are being told that although this problem is most likely a software problem which cannot be debugged at the dealership, and yet the dealership cannot ask the GM software engineers to investigate the problem given the symptoms because ‘GM doesn’t do this’. And when we ask what will be determined if we recreate it again at the dealership, we get vague answers that do not suggest that software can be debugged this way; only detected hardware problems. But we already know no codes are created (as determined last time). And when we ask if the dealership could start replacing parts in order to eliminate possibilities, we are told ‘GM doesn’t do this’ either since no parts are called out via codes. With all these seemingly inconsistent constraints, it’s difficult to see how we are going to get a resolution.
As stated previously, we would like to know the plans beyond recreating the failure again at the dealership to resolve this problem as we consider it both a safety issue and a risk of damage to the car’s engine and/or drivetrain.
The problem recreated on 6/10/13 again for the dealer.
Audrey