Mechanics

SPEED SENSOR

2002 Dodge Neon • 4 cylinder FWD Automatic • 154,000 miles

I have a 2002 dodge neon with an automatic transmission. My speedometer went crazy and then stopped working and my transmission started shifting erratically. I have replaced the input and output spped sensors and nothing has changed. Any ideas on what else it could be? Also can I replace the wiring harness that connects to the speed sensors and the throttle position sensor?
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Bobcat0422
March 27, 2011.




What's wrong with the wiring harness? Have you had the Transmission Computer checked for diagnostic fault codes?

Caradiodoc
Mar 28, 2011.
Im not sure anything is wrong with the wiring harness, just thinking it may be the wires that connect to the VSS. I had autozone do the diagnostic tests and came back with two error codes. P0500-VSS circuit condition and P1698- no CCD message from TCM.I dont know alot about the second code. Any ideas on what it could be? How hard is a TCM to replace? Is the VSS the only thing that could affect the speedometer and odometer? They still dont work and now my transmission wont shift past second gear. Please help! Thank you

Tiny
Bobcat0422
Mar 30, 2011.
The way this works is the input speed sensor tells the Electronic Automatic Transmission Controller (EATX), how fast the input shaft is turning, and the output speed sensor tells it how fast the final drive is turning. Essentially that is engine speed and wheel speed. The EATX uses that information to determine if slippage is taking place in any clutch pack and it sends that information to the Body Computer which sends it to the instrument cluster where it is interpreted. The cluster runs the speedometer which is a "stepper" motor. That is not a regular motor. It is four coils of wire that are pulsed by the computer to position the magnet in the middle. The pointer is attached to that magnet.

When slippage occurs in a clutch pack, or when there is a sensor or other electrical problem, a fault code is set, then the system goes to "limp-in" mode. That's where it stays in second gear so you can drive slowly to a repair shop without needing a tow truck.

The speedometer problem can be caused by any of the three computers, but the Body Computer and instrument cluster can't send the transmission system into limp-in. Based on the multiple symptoms, I'm pretty sure the speedometer will work once the transmission problem is solved.

Here are a few generalizations. If the speedometer DOES work, the two speed sensors are working. If it goes to second gear as soon as you shift into drive, suspect a sensor, pressure switch, or other electrical problem. If it starts out in first gear, then goes back to second gear during or right after an up-shift, suspect clutch slippage.

As for the codes, there are two wires that travel between all of the car's computers. They take turns transmitting information on them and reading information from other computers. It's possible the EATX isn't transmitting any information, but I've never run into that problem. Replacing that computer should be pretty straight forward. It should have one large 60-pin connector. Before you replace it though, be sure to check all the fuses.
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Caradiodoc
Mar 30, 2011.
I have 2001 neon a4 non autostick which has new battery, new speed sensors, new instrument cluster. Gearbox shifts as should, normally. I have p0500 error, speedometer and odometer not working and fuel level cauge going up and down when car tilts. Could the problem be eatx? Where is it located? As I understand eatx is sending signal to speedometer and this is propably the signal I am missing? Where do I start to seek the problem? Tcm is propably getting vss signal cause no limb mode? Thanks!

Tiny
Toitsu
Aug 23, 2011.

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