2000 dodge grand caravan sport, the check engine light is on, but no codes found after checking with reader, speedometer is jumping all over the place, from 0 to 120 mph, when the speedometer jumps around, vehicle gets jerky, as if loss of power, then surge, then loss. i have changed the speed sensor, it made no change, van still the same. please help

Any DTC'S - diagnostic trouble code's stored ?

Seed sesor fault. scan test your vehicle at auto zone for free. there are two speed sensors on this vehicle. replace both. not hard to replace.

speedo works with speed input and output sensors

Make sure to check the engine compartment fuses and the inside fusebox, if all the fuses look good then try to unhook the battery and then connect it back on and start the van and see if this helps. the radio is it asking for a code, if this radio has antitheft then you will need to install the code to make it work, look at manual and it will tell you how to do this. the code is entered using the preset staition buttons, there should be a card in the glovebox with the radio code if it has antitheft. if you find no bad fuses then you may have short out the cluster jumping it, but most of the time it just needs a fuse or reseting by removing neg battery terminal for about 2min, good day let me know the outcome.

Speed sensor. cheap to purchase and easy to change. This will solve the problem of speedometer and not shifting into overdrive.
Check engine light may go out or the codes will need clearing by disconnecting the battery for some time.

it may be a O2 sensor...have the codes read at an auto parts store...it will tell you for sure

Check for codes Before to do o think anything else.

Cycle the key on, off, on, off. on. Then count the flashes 12 is normal 55 is end of sequence

your van has an obd1 setup with dodge all you should have to do is turn key to ign to off 5 times without starting vehicle and the check engine light will flash the code for example it will start off with a code 12 i believe saying the computer is functioning the check engine will flash 1 pause flash 2 pause and will repeat a total of three times just write down all the codes when it gets to code 55 it is done hope this is helpful

0605 is for an Internal Control Module Read Only Memory (ROM) Error. This is typical of a malfunctioning computer. If the computer is bad, your retrieved codes are probably wrong anyway. May need to replace computer, drive, then see if if your check engine light returns.