I am working on a 1997 Chrysler LHS for friends of mine. I replaced the spark plugs and wires in it. Meaning I had the intake plenum off. Did the valve cover while I was at there. Put it back togather. It ran and shifted fine. Then 2 days later it went into limp mode wouldn’t come out of 2nd gear. Went in and read the codes. No codes what so ever. Drove the car no problems. It shifted and ran fine. Next time she drove it it did the same thing. Still no codes. Drove and shifted fine for me the next morning. It finally set a cel. It was a p0401 insufficient Egr flow. Check and the hose had got knocked of Egr valve to vacuum transducer. Put it back on that should fix that problem. Still no clue why trans is going into limp mode. Car has 169,000 miles. No tranny codes what so ever. Any body got an idea what is going on.

 

No codes at all? P0700?
Trans Input & Output sensors ? If the speedo works input sensor would be suspect.