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2nd Gen Ram Tech1994-2001 Rams: This section is for TECHNICAL discussions only, that involve the 1994 through 2001 Rams. For any non-tech discussions, please direct your attention to the "General discussion/NON-tech" sub sections.
Hey. I have a 98 1500 5.9 gas. 4x4. This is the second time I get this pair of codes set. P0420 catalyst efficiency below threshold and p0720 TCC circuit malfunction. Truck was running fine today but had the light on. New NKT o2 sensor a few months ago. Didn’t notice any drive ability issues. Just a note also had the abs and brake light on at the time.Any ideas on the codes, especially since they set together twice now.
P0720 would be Low speed senor above 15 mph, If you had a TCC code that could be P740 TCC no rpm drop or maybe P0743 TCC solenoid code. I would try replacing the speed sensor on the drive side on the tail housing of the transmission. Be care when the sensor is removed it will leak fluid.
Can you clarify if you had p0720 which is a speed sensor code or a different code related to the TCC ? And they always pop up together ?
My bad on the temperature, I edited that out of my post after i realized my mistake. I was going off the scanner I have which says 0720 is TCC malfunction, but more than likely it is a code for the speed sensor. This is the second time my check engine light has come on and both times I get those two codes together. Runs fine and don't notice anything out of the ordinary, except the money light is on.