Yesterday, one of the techs I work with drew a ticket on a 2006 Jeep Liberty with a strange complaint. The customer told him that, when pulling out of her driveway and making the turn on to the main street, the car would just stop going…no matter how much gas she tried to give it. It didn't happen all the time, but enough to be annoying.
The tech first thought of a possible transmission problem, and took the Jeep out for a drive. Finally, he was able to duplicate the complaint by making slow speed S-turns on the side street near our shop. Sure enough, when the problem occurred it felt like the engine wouldn't accelerate, not even with the pedal floored. Not a transmission issue as he first theorized, but an engine performance one.
He pulled into the shop and told me the story. He thought maybe a TPS issue, or a problem with a wire harness being stressed only in turns. The MIL was not on, however, and there were no codes recorded. He wasn't sure of how to proceed. The car only had about 35,000 miles on it, and neither of us knew of any pattern failure that met these symptoms. Sure, I've seen a few power steering pressure sensors fail, but we both thought that would affect idle quality only…not cause the engine to refuse to accelerate.
I asked if he had checked for TSBs, and wasn't to surprised at the answer. Depending on the source, nearly 40% of drivability issues, especially on low mileage, fairly new vehicles, are related to programming. That is one reason to make sure you always check for applicable TSBs on any issue you're diagnosing. Sure enough, he found a TSB covering this exact issue.
TSB# 18-049-07 applies to the 2006 Jeep Grand Cherokee, Commander, and Liberty. The fault is a programming issue for the ESP (Electronic Stability Program) system. Apparently, during "cloverleaf" style turns at speeds ranging from 25-40 mph, the ESP system thinks the vehicle is loosing control. It will then limit engine power and apply the brakes to the wheels it thinks are affected…in other words, it won't let you go. The problem is momentary, and you may or may not see the TCS light on the dash illuminate. No codes are stored, because the system is functioning as it thinks it is supposed to. The cure is a reprogramming to update the software.
Without researching the TSBs first, this tech could have been led on a wild goose chase, looking for a problem he would never find. Checking TSBs should be one of the first things you do when faced with a problem that you haven't faced before. It's not always a silver bullet, but it sure beats wasting hours chasing ghosts!
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