Piston Slap: The Fuel Hating Tranny

My question is for Sanjeev Mehta. I purchased a 2010 4 cylinder automatic Toyota Camry LE new and have been using it as my daily driver since. My commute is almost all city driving, so I noticed a quirk about the car right away.

During deceleration, the transmission seems to starve the engine almost to stalling, followed by a downshift and repeated until a stop is reached. This makes for a very jerky process for people like me that like to lightly brake for longer distances before stopping. I asked the dealership about it, they told me it was normal and it will go away after ”learning” my driving habits. Two years later, it still is around. From cruising the web and Edmunds, it seems all of the Camrys with the 6 speed auto suffer from this problem. My question is, why does this happen, why on earth would Toyota put this in their cars, and why has every professional review I’ve read of the car not highlight this problem? Is there anything I can do to alleviate this persistent problem? I had the dealership apply a TSB Toyota released for this issue a year ago, but it has not helped at all.

Sanjeev answers:

Do other TTAC writers have the same common/uncommon name mix up problem too? What say you, Jake Baruth, Stephan Lang and Derrick Kriendler? But, I know, I know…not everything is about me. So let’s do this thang.

After a bit of Googling, perhaps your dealer applied T-SB-0287-10:

“To improve the shifting performance and smoothness during acceleration, the Engine Control Module (ECM, SAE term: Powertrain Control Module/PCM) and Transaxle Control Module (TCM) calibration has been revised.”

But this link points to something more relevant, and interesting. Many (all?) electronically fuel injected vehicles cut fuel to the engine when “extended braking” in this manner. They’ve done it since the dawn of EEC-IV fuel injection on my super-precious Ford Fox bodies, that’s for sure. But ye olde Foxes (5.0V8, 4-speed auto) don’t bog very much at all as they slow down to idle. So what’s the problem?

When you slow down through 6 forward gears, the motor bogs down far more often than older vehicles with only 3 or 4 cogs to swap. When you combine this EFI program with the lack of low-end torque in modern engines (relative to the low revving engines from yesteryear) and the torque converter’s stall speed (and the computer programming added to it) you have a recipe for a boggy, clumsy downshift. In these “extended braking” situations, that is.

Simply(?) put, there are computer programs designed for maximum fuel efficiency, too many downshifting gears, computer controlled spinning fans (torque converter) and a relative lack of balls in rev-happy modern engines to ensure smooth downshifting. You’re gonna have to live with it.

Or change the way you brake. Or get a [s]Lincoln Town Car[/s] stick shift.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.