2006 Cadillac DTS downhill inadvertent acceleration problem

[wps]

Purchase Date:3/21/06

Today’s Date:08-02-06
Mileage about 3000.

2006 Cadillac DTS downhill inadvertent acceleration problem. The car is new.

This is a great car but it has some real quirks that I am not sure we can live with them.

1. We live in hilly country. When going down hill the car will accelerate with your foot off the gas pedal about every 100 yards depending on the grade. This is especially bad on the turns. You do not expect a car to accelerate with your foot off the gas peddle on a turn or any other time. This is a safety issue. The acceleration problem also happens while trying to park the car. It takes excessive use of the brakes to keep the speed down and drive in a safe manor. When going down a grade we shift the car into a lower gear. The speed limit in town and the residential areas here is mostly 25 to 35 mph and in town the car should not even be in drive. The only time in town that it goes into drive is when you let off the gas peddle. This causes the car to coast excessively. We run the car mostly in 3rd gear around town.

2. The max tire pressure is 30 on the door post, 44 lbs. on the tires. During the hot weather the pressure has gone up and the computer continuously flashes and makes noises. I lowered the pressure and it seems better.

3. The windshield wipers will run with the window completely dry, be sure not to leave the wipers on auto!

4. We are hearing a weird noise. It sounds as if it is coming from some part of the front of the car, also at around 70 mph. There is no message being displayed. It is a buzzing sound and it comes and goes. I tried opening and closing the sun roof. This did not seem to make any difference. We will be contacting the dealer to see if they have any answers.

These problems take the fun out of driving this car!!

The dealer has had the car for testing two times for several days. This surging is happening in parking lot as we were trying to park. The technician was not able to reproduce this problem in the parking lot, but was able to reproduce the other surging problem. This a built in computer function to save gas as explained to us by the dealer’s head technician. The technician said that the company has no repair for this car at this time. Unless there is a computer update, there is nothing to be done. While going down a hill the computer shuts off the gas. When the engine reaches about 1000 rpms the gas is turned back on. At this time the engine runs up 600 to 700 rpms. The engine does this continuously as you go down the grade. If you are going down a grade you have to put on the brakes continuously to keep the speed down. This situation becomes dangerous while going around the windy down hill grades in hilly country like where we live. Right as we turn into our drive way this happens almost every time. It happens even with your foot on the brake.

The cure for this is as I understand it from the technician and one of the owners at the dealer is to always drive in overdrive and use the brake instead of shifting down. This was their recommendation.

We have contacted Cadillac and they tell us there is no fix for this problem.

We contacted NTSB on May 1, 2006. They have not contacted us.

The acceleration problem is a safety issue the others are irritating.

wps

[dp102288]

I think any car speeds up as it is going downhill. All of our car do that.

But the other stuff is odd.

[wps]

This engine revs up 600 to 700 rpms when this happens and you surge or speedup while going downhill with your foot on the brake. It is in the computer program to save gas, so the computer shuts off the gas. It slows down great until the surge. When the engine slows to about 1000 rpms, then comes the surge. When the gas comes back on to prevent the engine from dieing the rpms go up 600 to 700 rpms. The engine has a lot of power and you really notice the surge. It is happening more in a parking lot, not good. You better have your foot on the brake. It is dangerous!

[codewize]

Something is wrong. Those symptoms are NOT normal. If the dealer can't fix it. Replace the car.

[ewill3rd]

The acceleration downhill is a normal condition, it's a function of the transmission. There is no engine braking in automatic overdrive.
Engine braking is when you let off the gas and the compression from the engine slows the car down because the components are linked together, like in a standard transmission with the clutch pedal up. On an automatic trans, internal components must "hold" in order for engine braking to occur, on that transmission they let the components "free wheel" in overdrive so the car will coast when the pedal is released.
You should be able to get engine braking in manual 3rd if you really want it.
Most GM transmissions are designed that way. Some transmissions have holding clutches that allow engine braking in 4th gear but it depends on the specific transmission.
If you are pointing down hill in 4th gear it's going to roll faster. If you are not going over about 60 mph just drive the car in the 3rd gear selection position, you'll have engine braking and it shouldn't adversely affect your fuel economy unless you are cruising over 60mph.

The tire pressure on the door plackard is the "recommended" tire pressure, not the maximum. The tire pressure on the side of the tire is the MAXIMUM pressure, meaning don't go over that. Both pressures are cold inflation pressures. Air expands as it gets hot. The pressure in a tire will be higher after driving it than it will be when it sits overnight. Tire pressures should be checked cold, if you have been driving it you should make the pressure higher to adjust for the temperature of the tires and the air inside.
The MAX pressure is not the recommended pressure, for seemingly obvious reasons.

If you have rainsense there is an optical sensor on the glass, if a bug, or road dirt gets on the glass over the sensor the wipers will activate. You are correct, don't leave them in auto mode if you live where this happens a lot.

As for the noise, I am sure your dealer will make every effort to identify the source of the problem. Any information you could give them on when it does it would be helpful in allowing them to duplicate and isolate the problem area.

Good luck, hope this helps.

[wps]

Thank you for response. OK on everything except the downhill acceleration problem. We do shift down depending how fast is reasonable for the road we are on. It could be 1st, 2nd or 3rd. In some of these cases the speed limit could be anything from 15 to 35 mph on the particular road around town and in the subdivisions. This country is very hilly and windy in the Sierras of California. When it surges in the parking lot the car is either in 1st or 2nd because the speed is so slow in a parking lot. The surging seems to be worse in the lower the gears. 600 to 700 rpms is a considerable jump. Cadillac and the dealer have told us this surging is the computer program and cannot be changed unless Cadillac changes it. During deceleration the gas is shut off to save gas, when it comes back on you get the 600 to 700 surge. Given there is no engine braking in automatic overdrive. On long downhill grades we do run in 3rd. On flat land the car performs like a dream in drive. We get 24 to 25 mpg on the flat.

I know what you are saying about a specific automatic transmissions that shift down, Allison is one of them, sure is nice.
wps

[codewize]

Again, these symptoms are NOT normal. I've been driving GM mostly Cadillacs all my life and I have never experienced anything like what your describing, especially in a parking lot.

The RainSense II wipers will turn on for other things when you don't see a reason. I find this happens sometimes at high speeds when I'm following a truck or something. I have never seen it happen due to dust, dirt or bugs. You make it sound like it happens far more than it should.

Yes the tire pressure on the door sticker is the recommended pressure for the car. The pressure on the sidewall is the max rating for that tire.

No noise in a brand new Cadillac is expected or acceptable. I continue to comment on that fact that my car is as quiet at 75 MPH as it is at 20 MPH. I find it amazing that the car remains that quiet and handles as if nothing changed. Truly amazing engineering.

[wps]

Codewise:
Thanks for your responses. I don’t think the surging is normal either. Keep in mind it does this mostly when you are going down a steep hill in the lower gears. In the parking lot is sure not normal. We will see what the powers to be have to say. I haven’t had time to see about the noise yet. I turned off the RainSense, it is painful to see the wipers go across a dry windshield.
wps