Lateral72

My parents bought a used 2009 Suburban LTZ a few months ago (50K, 5.3L, 4wd). I was visiting and got to drive it for an extended amount of time. There's a couple things I've noticed, that I'm wondering if they are normal or not.

- Engine Braking while stopping. I've never had any automatic car/truck do this before. While braking, the trans feels like it's locked up and engine braking the truck, as if it were a manual. The RPM's do drop significantly before down shifting to the next gear. So much so that if the A/C is on high, it will drop with the RPM's.

- Rough Idle. From what I've read, this is kinda normal. It's not a constant rough idle, but every 10 seconds or so the engine will hiccup. I will suggest standard cleaning, seafoam, plugs, etc.

- Switching from 2wd to 4-Hi or 4-Low takes 5-7 seconds or so to engage. How the heck does Auto work if it takes so long to switch? Truck will be in a ditch long before 4wd engages if you hit ice..


Aside from the engine braking and rough idle, the engines/trans runs good. No surging that I've noticed, plenty of power, etc.

SabrToothSqrl

if it's operating properly

1. engine braking should only be occurring in TOW/HAUL mode (or manual shift mode)

2. I'd throw in some new plugs and new air filter

3. You really need to learn more about the mechanics of the system before complaining about their function.

2WD is hopefully fairly evident; power goes to the *** end.

in 4WD you are actuating the front half shafts, effectively locking in the hubs, but it's in the shaft, not the hub, while sliding a chain in the transfer case to power the front drive shaft.

4WD auto leaves the transfer case in 4WD while leaving the front axle actuator (not sure of the correct term, but I can point them out). disengaged. If slippery conditions are detected, they will engage quickly and remain engaged. I'm not sure of the protocol to disengage them. perhaps shutting it off or a period of time or MPH.

I did notice an odd shift pattern and braking on my 09 as well, it fades after a while.

so, other than the idle, of which mine is so smooth you can't tell it's on, you are fine...

Lateral72

Thanks for the response. I'm not a truck/suv/4x4/etc type of car-nut, so I really haven't had the need to figure out transfer cases, and such.

Unfortunately there maybe a problem, as it was doing the engine braking/aggressive downshifting not in Tow/Haul. I'll swing by this weekend to double check, but it may end up at the dealer next week.

73shark

Welcome to the forum.

Not sure what you meant by the A/C dropping in rpms w/ the engine speed. Since the A/C blower is electrical, if it slows down w/ engine rpm, then that sounds like the alternator and battery are not functioning correctly. Hard acceleration does cut out the compressor.

Re: rough idle, I'd first check to make sure all of the plug wires are firmly connected then run some Techron thru it.

Lateral72

Thanks for the help guys.


As the truck is coming to a stop, the torque converter is staying engaged. As the truck downshifts through the gears, the rpms will drop with each gear. When the RPM's are at their lowest point, just before a downshift, the a/c blower will slow down with it. The RPM's drop quite low before the trans will downshift, usually about the same RPM as idle. From what I remember the engine braking/shift points seem to depend on how hard you brake. If you brake gently, it's not very noticeable (though it's still engine braking itself), if you brake hard, the engine braking is very aggressive and the a/c blower (when on full) will dip with the RPM's.

This all happens while in "D"rive and not in T/H

Every other A/T truck or car I've driven simply unlocks the converter, and you're basically free-spooling as you brake. Then the trans will re-lock up and select whatever gear you need when you get back on the gas, or stop completely.

73shark

All I can say is that the blower is independent from the engine rpm save for voltage fluctuation. So if what you say is happening, then there's a problem separate from the way the tranny is responding.

Lateral72

I completely understand what you're saying about the blower. But I didn't notice any other times when the alternator seemed to be under performing. I'm just more concerned about the engine braking, when apparently it shouldn't be.

73shark

I'd have the battery and alternator checked just to rule them out. Most auto parts stores will do it for free.

Does the engine braking seem to occur at all speeds when slowing down or just slower speeds?

Chevrolet Customer Service

Lateral72,
Did you end up taking the Suburban to a dealership this week? If so, how did everything go?

Sarah (Assisting Louis), Chevrolet Customer Service