OBD II P0720 Code


knlc
11-06-2004, 10:17 AM
RE: 1998 Durango, 5.9 liter V8. The speed sense circuit is malfunctioning. My shop manuals do not address replacing the sensor-- does anyone know the where the speed sensor is located?

DurangoDave
11-07-2004, 04:35 PM
It's on top of the rear differential. Very easy access if you raise the entire rear of the car on jack stands, and remove the spare tire.

Use a metric wrench to take the nut off the stud, disconnect the electrical connection, remove the clamp that holds the brake lines down, and then use the next size metric wrench to remove the stud from the differential. (I can't remember the wrench sizes....I think the first nut is 13mm and the stud itself is 14mm).
Take a pair of channel lock pliers and twist the sensor out of the differential housing...it's just a friction fit with an o-ring....might need to help it out by prying with a screwdriver blade.
I'm not sure if the computer needs to be reset or not to make the abs and brake lights go out...I was told it is not necessary, but I did it anyhow before I started the engine, so I don't know if it was really required. Anyway, if you need to reset the computer, disconnect the battery + cable, then hold the ignition key in the "start" position for about a minute. Wait a half hour or so before reconnecting the battery and starting the car.
IF the problem was really the speed sensor, the lights will go out and the speedometer will also start working properly again. (The problem could also be the abs module itself, apparently).
The speed sensor is about $50 USD at the dealer, (I couldn't find it at the parts store). Apparently the abs module is $hundreds.
Dave

knlc
11-10-2004, 11:08 PM
Thanks.
My Haynes manual indicates that the code from my code reader means the output shaft speed is less than 60 rpm with vehicle speed above 15 mph (low output speed sensor rpm above 15 mph).
I went to the Dodge dealership and the mechanic said the sensor I needed was at the transmission, just prior to the engine. He did mention the rear sensor but said that the transmission speed sensor was probably the culprit.
The cost was $15.06 at the dealership.
If this doesn't work, I'll follow your advice.
Thanks again.

hundahunta
11-10-2004, 11:41 PM
it is located at the driver side rear of the trans..use a 1-inch deep socket. takes less than 5 minutes good luck.. also if you replace it I would just check the old one for resistance more than likely it will be an open circuit GOOD LUCK

knlc
11-26-2004, 08:39 PM
The Speed Sensor at the transmission was the culprit. I did check the resistance on the old Sensor, and it did have an open circuit.
Problem solved-- thanks for your help.
By the way, this is the second sensor; the first ws replaced under warranty at around 30,000 miles; at that time, it gave no code, but the transmission was slow engaging after the car sat for 3 days or longer. The shop replaced the sensor and the transmission then engaged properly.
I had the same problem in the current instance, but this time I also had the check engine light, and received the p0720 code.

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