1997 Aerostar. Speed sensor issues.

[ffracer69]

I have a 97 Aerostar Cargo van that I picked up used some time ago. I've never had any problems with it other than the usual wear and tear type things that go along with any older vehicle.
I have to pass an emission inspection in order to renew the tabs and it is failing because it keeps throwing a P-0500 code.
All of the reference material I have access to tells me that this is a Vehicle Speed Sensor fault.
I've installed a new sensor in the differential housing, cleaned the differential and changed the lube to eliminate any extra metal contaminates.
I'm still getting the P-0500 code.
If anyone can point out something that I might be overlooking, or suggest a method to troubleshoot this problem, I will be eternally grateful!

 

[BrooklynBay]

Welcome to this forum! Do you have any issues with the cruise control, ABS brakes or the transmission?

 

[ffracer69]

Thanks for the fast response, BrooklynBay!
I have had intermittant problems with the cruise control kicking out and with the transmission not wanting to up-shift. This might happen once in a month of daily driving, or it might happen several times in one day.
I've been trying to track the problems down to a specific component without any success.
So far I have not had any issues with the ABS, but the prior owner told me that sometimes the brakes seemed "touchy".

 

[BrooklynBay]

Check the wiring going to the sensor on the rear differential, and the internal reluctor ring inside the differential.

 

[ffracer69]

I've done a thorough inspection of the reluctor ring when I cleaned and changed the differential lube. Took a good look at the connector to the sensor then as well, and everything looked good. I guess it's time to start checking continuity for the wiring, but i dont have any good reference material that shows the wiring diagram for the speed sensor circuit. If I'm understanding it correctly, the speed sensor feeds the ABS and the ECU, so there has to be some interconnection. That would seem to be a likely area to start looking for this kind of problem.
Any idea of where in the wiring I should look?

 

[BrooklynBay]

The two wires going to the speed sensor are color coded. Follow the wiring harness with those wires until you can't see it anymore, then look for the same color codes inside the vehicle. It's a good idea to get a schematic diagram of the circuit.

Do you use the tilt steering option in the steering column? Sometimes the wires could develop cracks on the insulation, and short against the inner column. This could create issues with the cruise control, shift points of the transmission, codes, etc.

 

[ffracer69]

Problem Solved

After BrooklynBay's last reply, I traced the wiring for the speed sensor and did a continuity test on the circuit. Point to point everything checked out fine.
In the process of disconnecting and reconnecting the wiring I discovered some light corrosion on the connector terminals, cleaned them thoroughly, reconnected, cleared the ECU again, ran through multiple drive cycles, and the problem no longer exists!
The van now shifts better and there are no more problems with the cruise control dropping out intermittently.
:biggthump:
Thanks for getting me on the right track!

 

[BrooklynBay]

Thanks for the update! It's a good idea to use an anti oxidant cream inside the connector to prevent moisture from getting in. They use this on light bulbs sockets, and battery terminals.