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2006 GXP downshift issue

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steamythekid

New member
I recently bought an 06 GXP, when I test drove the car and drove the car home everything seemed fine. Drove it to work the past two days and have noticed when stopping it feels like the trans is fighting the brakes because its not downshifting at the proper time. The car will only do this below 25mph when it should be downshifting into 1st gear and once under 10mph it will go into first, otherwise the transmission shifts great.

The traction control light and service stability control message are currently on in the car, I will scan the abs system and see if there's any codes in there and will try to see if I can get the tap shift sytem to downshift properly. Has anyone else run into issues like this? I know it will likely end up being internal damage to the trans and end up being a rebuild or replacement but has anyone diagnosed an electrical issue such as a wheel or trans speed sensor to produce a similar issue?
 


I don't really understand what your issue is. Can you describe it better? The transmission isn't supposed to downshift into first gear when you're coming to a stop until you get below 10 mph. Mine typically shifts at 7 mph. So it may be something normal for this car that you're just not used to.
 
derpyimp said:
I don't really understand what your issue is. Can you describe it better? The transmission isn't supposed to downshift into first gear when you're coming to a stop until you get below 10 mph. Mine typically shifts at 7 mph. So it may be something normal for this car that you're just not used to.
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Sorry should've worded it better, when slowing down from about 25 I'm getting a shudder that doesn't seem normal and it feels like the trans is fighting the brakes to stop. RPM drops low to about 5 or maybe 600 (which might be normal for these I'm not entirely sure) while stopping and the downshift feels very sluggish and delayed not a very smooth transition,feels like I have to put my foot into the brakes much more than I should have to. Scanned it and it came back with no dtc's but it has two bad abs sensors and a stability code but nothing from the trans. I did notice that under a wot pull that I'll get a clunk after letting off that sounds like a motor or trans mount that may also be the culprit under braking.
 
So the shudder occurs right at 25 mph, or constantly as you're slowing down, or intermittently? Both of my cars with the 4T65E have over 100k miles on them and will give a bit of a clunk or shudder when they downshift into 1st while coming to a stop. I don't know if it's normal or due to components wearing out, but either way, it hasn't caused any major issues for me.
 
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derpyimp said:
So the shudder occurs right at 25 mph, or constantly as you're slowing down, or intermittently? Both of my cars with the 4T65E have over 100k miles on them and will give a bit of a clunk or shudder when they downshift into 1st while coming to a stop. I don't know if it's normal or due to components wearing out, but either way, it hasn't caused any major issues for me.
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Constantly below 25, the harder on the brakes the more noticeable it becomes.
 
I'd check those motor mounts, both below the engine and especially the front dogbone mounts. Maybe could be warped brake rotors too, but I would think that would show up more during light braking than hard braking.
 


It feels like the TQ Converter isn't letting go as you slow to a stop. Car is sluggish.... and the brakes aren't feeling too brakey.

These are side effects of the Traction Control system having the light on. Fix the Wires to the front ABS sensors, or the bad hubs, and the trans and brakes will prob feel nice again.
 
Gregorius said:
It feels like the TQ Converter isn't letting go as you slow to a stop. Car is sluggish.... and the brakes aren't feeling too brakey.

These are side effects of the Traction Control system having the light on. Fix the Wires to the front ABS sensors, or the bad hubs, and the trans and brakes will prob feel nice again.
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Will do looks like left front and right rear are throwing codes
 
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I have the same shudder problem on my '08 GXP. The drivetrain shudders whenever I slow down below about 20 mph. It acts as though it's stuck in a higher gear instead of downshifting like a normal trans. If you shift to neutral before stopping, there is no shudder, or if you operate in the manual mode, there is no problem.

I took the car to a transmission shop today and they said the transmission is in very good condition--nothing wrong. The technician said the problem is the DOD system being in the 4 cylinder mode, which causes the engine to vibrate at low rpms.

This shudder is not a normal condition for these cars--I've owned another--a 2007 when new. There was never a shudder problem. This car has 160,000 miles on it.

Does anyone have suggestions on troubleshooting the problem?
 


^one idea is deactivate the DoD and see if it fizes the issue. also with 160k miles, might be a good idea to possibly replace the lifters as I heard that because of the DoD/AFM it causes lack of oil in the lifter valley and causes some of the lifters to fail.
 
bocoogto said:
I have the same shudder problem on my '08 GXP. The drivetrain shudders whenever I slow down below about 20 mph. It acts as though it's stuck in a higher gear instead of downshifting like a normal trans. If you shift to neutral before stopping, there is no shudder, or if you operate in the manual mode, there is no problem.

I took the car to a transmission shop today and they said the transmission is in very good condition--nothing wrong. The technician said the problem is the DOD system being in the 4 cylinder mode, which causes the engine to vibrate at low rpms.

This shudder is not a normal condition for these cars--I've owned another--a 2007 when new. There was never a shudder problem. This car has 160,000 miles on it.

Does anyone have suggestions on troubleshooting the problem?
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Looked into this today and you're absolutely correct, pulled the oil pressure switch to deactivate the dod and took it for a drive to see if it made a difference and no shudder when stopping.
 
Is that the switch on top of the engine in the valley area? Do you just remove the wires to disable DOD? Is that the prescribed way to disable DOD for test purposes?
 
I tried today putting the shifter in Manual, driving in 4th gear, stopping. The shudder occurs exactly as it does when in Drive.

If I manually downshift while slowing down, so I'm in 1st gear at 15-20 mph, the shudder does not occur.

Does driving in Manual disable DOD?
 


Do those cars have a real time MPG thing that says if it's in V8 or V4 mode? Maybe that's just a truck thing.

Otherwise I don't see anything in the tune that says tap shift disables the DoD. It says it's active in 3rd and 4th gear no matter what but the transmission files does not specify if the TUTD paddles disables anything.

Pulling the oil pressure switch connector is fine to test, the system will disable if the switch in unplugged.
 
No. There's no indicator in the car. I'll try the oil pressure connector. Is it the one in the valley near the injection?
 
rottonj,

Thanks for the suggestion. I'll try it. There is now synthetic fluid in the trans with about 3,000 miles on it.

If hte shudder is due to the trans, the transmission shop was wrong when they told me the trans is in good shape.
 
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