First lets clear up some misconceptions. When the Check Engine light turned on, there was a diagnostic fault code stored in the Engine Computer. For future reference, Chrysler makes reading those codes easier than anyone else. Cycle the ignition switch three times from "off" to "run" within five seconds without cranking the engine, then watch the numbers show up in the odometer display. It is important to understand those codes will never say to replace parts. They only indicate the circuit or system that needs further diagnosis. In this case I would go back to the shop that replaced all four oxygen sensors and find out what diagnosis led them to that. It's not terribly common to have one fail, and certainly not all four at the same time. If they did get a fault code for one of them, that code would have specified which one, then the proper course of action is to watch on a scanner what it's doing while the engine is running. Extra air, then propane can be introduced to verify the sensors change their readings and detect the lean and rich conditions. After everything else is ruled out, then the sensor can be determined to need replacement.
Also understand the two front oxygen sensors tell the Engine Computer how well it's controlling the fuel / air mixture for best fuel mileage and performance, and lowest emissions. All the two rear sensors do is monitor how well the catalytic converters are working. They have no effect on engine performance. There are well over 1000 potential diagnostic fault codes and some of them get real specific. A code for "catalytic converter efficiency" is vastly different than the code for a defect with the sensor.
You can't go by smell either with catalytic converters. One out of a hundred failures might result in the rotten egg smell and that is usually accompanied by real high fuel consumption. Sometimes the converter will melt inside and become plugged. Sometimes the catalyst breaks apart and flies out. Anything that causes it to not change the composition of the exhaust gas is what is detected by the rear oxygen sensors, and that's when it sets the appropriate fault code.
Where part of the problem might have come in is one place read the code(s), then a different shop replaced the parts. The auto parts stores do a nice service in reading the codes for free, but they're in the business of selling parts. Most of the salespeople are good at their jobs but they never were mechanics and they don't have the same experience. If your son simply requested the guy at Firestone replace some parts, he got what he asked for. What he should have asked for was for them to diagnose the cause of the fault code, then let THEM decide how to solve the problem. (Think of ordering a steak at a restaurant. If you tell them how to cook, and they do it right, you can't blame them if you don't like it. You got what you asked for). If the mechanic decides what is needed, and the problem comes right back, he obviously diagnosed it incorrectly. Electrical parts are a troubling area because new ones usually can't be returned once they're installed, but ideally, the proper thing to do in a case of a misdiagnosis, is to start over with the diagnosis, take another stab at solving the problem, THEN reinstall the old parts if possible.
The reason I suspect your son just asked to have parts replaced is that when he went back, that's when they wanted 99 bucks for the diagnosis. If they had already charged him for that, they would not charge again since it's the same problem and they misdiagnosed it the first time. That would also coincide with the $460.00 charge. Oxygen sensors aren't cheap. To buy four and have them installed, I would have guessed the bill would have been higher.
Next, there are times when computers are "reflashed" with updated software but that is usually to address installing a replacement or if an emissions problem has been identified by Chrysler. Normally a reflash is not needed today if it was running fine yesterday.
The place to start now is by reading those codes by cycling the ignition switch. We can get an idea of where to go next and what to check.
Tuesday, February 26th, 2013 AT 2:08 AM