You will not hurt the transmission by driving in limp mode but you will destroy the engine. Limp mode was designed in so you could drive slowly to a repair shop without needing a tow truck. A safe speed is up to 20 or 25 miles per hour. How long do you want to drive that slowly?
I have read about people who didn't understand what was happening and they tried to drive 65 mph in second gear, then were angry with Chrysler when the engine flew apart. No passenger car engine is designed to go that fast. Race car engines can go that fast with the hope they will hold up for 500 miles.
The reason the transmission works sometimes is you get it out of limp mode by turning off the ignition switch and restarting the engine. When it goes into limp mode again intermittently, either there is an intermittent electrical problem, usually a corroded splice or loose terminal in a connector, or there is slippage taking place in one of the clutch packs. Years ago, before Chrysler was the first to introduce this design in 1989, transmissions would give you a year or two of warning that the clutch plates were wearing out. Shifts were mushy instead of crisp and solid, and "engine runaway" was common. That's were the engine would speed up during an up-shift until the next gear finally locked up.
With this design, those clutch plates still wear out at the same rate, and the transmission still will need to be rebuilt at about the same mileage, but you don't get that year or two of warning. The Transmission Computer watches the volume of fluid it takes to apply each clutch pack for the various gears. When it sees one is taking more fluid, meaning the plates are worn down, it will engage the next higher gear during an up-shift, like normal, but it will delay releasing the previous gear for a fraction of a second. That produces a solid shift that feels like when the car was new, ... Until the day it can't update any further. That's when some slippage takes place and is detected, and it goes to limp mode.
At the mileage you listed, you're way overdue for a transmission rebuild, but given the age of the van I'm guessing it sees a lot of highway driving. There isn't much shifting going on so there won't be a lot of clutch plate wear. Regardless, the fault code you listed refers to an electrical problem and it could be as simple as a relay with bad contacts, or I suppose as serious as a computer that isn't recognizing the change taking place in a signal voltage. Your mechanic will have a diagnostic manual that will spell out the troubleshooting steps. If you take it to a transmission specialty shop, they will have seen this before and will need relatively little diagnostic time to come up with a repair estimate.
Be aware there are some shops that will automatically want to sell you a transmission rebuild because that is what they do, and given the mileage they may be able to justify their recommendation, but there is another test they can do if they have legitimate concerns. Chrysler built in some diagnostic software into the Transmission Computers. What you're interested in for this is called the "clutch volume index", (CVI). That is a set of four numbers corresponding to the number of ccs of fluid it takes to apply each of the four clutch packs. As the plates wear down, it takes more and more fluid to fill in behind them to apply each pack. An experienced transmission mechanic can tell by those numbers how much life is left in them. If they're close to being used up, he will recommend a rebuild along with diagnosing and solving the electrical problem. If you decline the rebuild, you are very likely to find the transmission will work perfectly fine after the electrical problem is fixed. That would incline you to think the mechanic was trying to rip you off by pushing the rebuild. In fact, he is typically looking out for your best interest in the long run. He knows that for most people that slippage I talked about is going to start to occur real soon. If you haven't had any transmission trouble up to now, that is proof your case is different due to lots of highway driving. It's entirely possible you may get another year or two or three out of it before a rebuild is needed.
Friday, September 20th, 2013 AT 12:50 AM