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DaveTheCarGuy, Car Enthusiast
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Experience:  AAS in Automotive Technology.
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Cadillac dhs: Vehicle: Cadillac Deville. Year 2001. Mileage:

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Vehicle: Cadillac Deville. Year 2001. Mileage: 278k. I will be driving along and the car acts like I have downshifted abruptly slowing the speed from apr 35-45mph to nothing. This comes without warning, happens any time of the day, has always been on dry pavement, most of the time has occured at the end of a turn (either direction) but has also happened while going straight. May not be a factor but only seems to happen when the air temp is mid 50's. I don't want to be a parts replacer to find the problem and it is too good a car to let go. Thanks
Hello and thank you for using

My name is XXXXX XXXXX I will be helping you with your issue. To ensure I can give you the best possibly answer, I need some more information.

Are you saying the car will go from 35 - 45mph to a complete stop?

Is this while your foot is on the gas, or off the gas? Does depressing the gas pedal have any effect?

Have you had any recent service performed on the vehicle?

Does it have a CEL or any warning lights?

Do you get any vibration in the brake pedal during normal driving?

Customer: replied 3 years ago.

Hello Dave: I will widen the speed range for you. 20 to 45 mph. When it happens the car acts and sound like a "jake Brake". The accelerator has always been engaged and the speed will suddenly drop to approximately 2 or 3 mph. Feathering the gas will have no effect other than to keep the car moving. Generally this will last for roughly 20 seconds and then go back to normal operation. No recent service other than oil change. The traction control light comes and goes and the event happens so fast and without a mechanical warning that I can not say if it is on prior to the event. No discernible vibration or pulsing in the brake pedal during normal driving.


Thanks, Mike

Hi Mike,

This is an interesting issue. My first instinct would be to check the Crankshaft position sensor(CKP). The reason why I say that is the traction control system is tied to the CKP, and if the CKP fails, you will loose spark, causing your engine to become a brake. Does the tachometer fall to zero faster than the car is slowing down by chance? Sadly, there is no easy way to test the CKP without an Oscilloscope. Even then, if your issue is not constant, testing for it is near impossible. Other things that might help point at the CKP would be it happening more frequently when it is wet outside. The CKP is all the way at the bottom of the motor, and many times when it has an intermittent failure it can be set off by water which it easily contacts, Especially when turning (splash/splash-back from the wheels).

The other thing to check would be the Throttle position sensor(TPS). If the TPS has a "dead spot" in it, it can cause running issues that are corrected when throttle position is changed.

Customer: replied 3 years ago.

I think we need to look a little further. This problem has always come on in dry conditions, no rain or puddles. The engine does not stall and tachometer is consistent with speed. The problem has been most associated with a gradual turn however it has also occurred on a straight run. Any other sensors we might need to look at?


Thanks. MIke

Hi Mike,

The CKP doesn't only fail from water(just one of the common ways), so I still think you have a possibility there. The only other thing I can think of is you getting put into limp mode. Limp mode will not always trigger a CEL, and if it is from the transmission, you might need a GM Tech II (or equivalent) scanner to read the transmission codes.

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