Buick Enclave 2015: Stuttering sound shortly after shifting into Drive

juggler46

I hear a "stuttering" sound from the front of the vehicle. This sound occurs on most ignition cycles, a maximum of once per ignition cycle, and it seems to occur shortly (5-10 seconds) after shifting into "Drive" for the first time that ignition cycle. It lasts for maybe a second or a bit longer, and I hear a total of 10-12 "beats" in rapid succession. I have never heard this sound when in "Park" or "Reverse".

It sounds as though some actuator is "trying" to turn on, and stops after about a second of trying. (I'm not sure whether it succeeds or fails.)

No codes are generated by this, and I don't notice any ill effects on the vehicle's drivability or systems. I am, however, concerned that something related to this sound is getting ready to fail. There is a little over 2k miles left on the GM Certified warranty, and I'd like to figure out what this is before GM stops footing the bill for repairs. Dealer could not reproduce the sound (or didn't notice it, more likely) on their test drive.

Some fairly extensive brake work was done on the vehicle shortly after purchase (about 8 months ago), but this sound may or may not be related to that.

Does anyone have any idea what could be causing this?

thecardoc3

imidazol97 is right on target with the ABS self test routine. It usually occurs in three stages with GM systems. The first occurs right at key on where the module powers, a solenoids and sensor circuits are tested. The wheel speed signals and some of the solenoids and pump motor are tested at 9mph and then any final testing occurs at 15mph. Most of the time it isn't noticeable to the average driver but occasionally everything else is quiet enough to get someone's attention.

imidazol97

Thanks for your info. The Cobalt FSM didn't mention a higher speed test for it other than the 8/9 mph cycle. Nor was the primary test at key ON mentioned. Perhaps the tests vary with the brand of unit employed by each car.

I still haven't noticed my Malibu's ABS testing. I know I have noticed it in the past. But they are a lot less noticeable than my 98 and 2003 leSabre's ABS.

I can understand the original poster being concerned there was something that might degrade into a problem happening. The testing of the ABS is timed to occur so it's covered by HVAC fan, radio, and/or the accelerating engine noise. Most people never notice it. But once it's noticed, it like a pimple on the forehead. Just can't stop pickin it.

imidazol97

juggler46 said:

I hear a "stuttering" sound from the front of the vehicle. This sound occurs on most ignition cycles, a maximum of once per ignition cycle, and it seems to occur shortly (5-10 seconds) after shifting into "Drive" for the first time that ignition cycle. It lasts for maybe a second or a bit longer, and I hear a total of 10-12 "beats" in rapid succession. I have never heard this sound when in "Park" or "Reverse".

It sounds as though some actuator is "trying" to turn on, and stops after about a second of trying. (I'm not sure whether it succeeds or fails.)

No codes are generated by this, and I don't notice any ill effects on the vehicle's drivability or systems. I am, however, concerned that something related to this sound is getting ready to fail. There is a little over 2k miles left on the GM Certified warranty, and I'd like to figure out what this is before GM stops footing the bill for repairs. Dealer could not reproduce the sound (or didn't notice it, more likely) on their test drive.

Some fairly extensive brake work was done on the vehicle shortly after purchase (about 8 months ago), but this sound may or may not be related to that.

Does anyone have any idea what could be causing this?

I'd have to check again, but on my Cobalt and my Malibu there's an ABS cycle after starting that may be like what you're hearing. It's so quiet and well-timed in the operation, I don't notice it other than maybe 1 time out of 100. I'll stay aware as I drive my two as to when this cycling occurs and post back.

juggler46

imidazol97 said:

I'd have to check again, but on my Cobalt and my Malibu there's an ABS cycle after starting that may be like what you're hearing. It's so quiet and well-timed in the operation, I don't notice it other than maybe 1 time out of 100. I'll stay aware as I drive my two as to when this cycling occurs and post back.

Thanks for the reply. I just stumbled across some discussion on another site that indicates it might be some ABS pump diagnostic. I will try to observe more closely at what speed the noise begins. (I've seen some postings that say 7mph, and others that say 19mph.) It's always at relatively slow forward speed, but I've never noted an exact mph. If it's repeatable at a given speed, I'll feel better about it.

imidazol97

I think it will be just as you start to accelerate. That was the noise of the engine and the acceleration feel tend to cover the vibration.

You might be able to lightly hold you foot on the brake pedal as you start. It may still do the cycling on the pumps. I believe it did that on the leSabres I had. I don't know about my two current cars. It may not cycle the pumps until the vehicle has sat for a certain period of time, such as overnight. I didn't notice the Cobalt doing it today when I ran an errand. I'll watch tomorrow morning.

imidazol97

Cobalt factory service manual says ABS unit cycling occurs on that application at 9 mph. I assume that can be going forward or backward if someone has a long, fast driveway...

juggler46

I haven't driven the Enclave since I first posted, but I was able to watch the speedometer once while my wife was driving. My best guess was around 15mph when I first heard the noise.
She's driving my son to his summer job this morning -- I told her to have him watch and note the speed when he hears that noise, just to gather a bit more data.

juggler46

thecardoc3 said:

imidazol97 is right on target with the ABS self test routine. It usually occurs in three stages with GM systems. The first occurs right at key on where the module powers, a solenoids and sensor circuits are tested. The wheel speed signals and some of the solenoids and pump motor are tested at 9mph and then any final testing occurs at 15mph. Most of the time it isn't noticeable to the average driver but occasionally everything else is quiet enough to get someone's attention.

Thanks for the information. My wife said she and my son listened the last couple times they drove, and thought they heard the noise around 15-18mph.

juggler46

imidazol97 said:

I can understand the original poster being concerned there was something that might degrade into a problem happening. The testing of the ABS is timed to occur so it's covered by HVAC fan, radio, and/or the accelerating engine noise. Most people never notice it. But once it's noticed, it like a pimple on the forehead. Just can't stop pickin it.

Yep. I considered turning the radio up to avoid noticing it, but that didn't seem like the smart thing to do at the time.

Maybe when the GM Certified warranty runs out, I'll turn the radio up all the time...