[JimLev]

Do you know what the actual code # is? P0500, P0501, P0502, P0720?? I don't see any reference to IMPELLER in the code listings in Hayes, but the above OBDII codes deal with vehicle speed sensor/output shaft speed sensor.
The VSS (99 and earlier) or OSS (2000 and newer) in the transaxle control the shifting of the tranny and supply the computer with speed info for the speedometer, etc. This is a ~$30-40 part and may be the problem. Look in your Hayes (#36075) manual on page 6-14 (#13).