94 toyota camry v6 error code 500 ,720

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#1
Help! I have a 1994 toyota camry 6 cylinder. I get a check engine light and codes 500 and 720 and the o/d light flashes. Also, when I start the car in the morning the speedometer jumps up to 30 and slowly goes down to zero. As I drive, sometimes it will miss a shift and I have to take my foot off the gas. I was told that I should change the vehicle speed sensor. I swapped the vehicle speed sensor from a 1997 toyota avalon 6 cylinder (same part) and still had the same problem. I ordered a used instrument cluster and installed it. Still got the check engine light and the trasmission still did not shift correctly but the o/d light did not flash. I took the car to a transmission shop and I was told it was the vehicle speed sensor and that I should start with that. Having already swapped it out, I don't know where to go next. I was wondering if you had any idea as to what I should check next.
 

csaxon

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#2
Did the speed sensor you replaced have the gear drive attached? Somethimes the gear teeth break or the circlip comes off.
 

csaxon

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#5
The 541 trans uses an elecro-magnetic direct clutch speed sensor to determine shift timing and hydraulic pressure.
 

csaxon

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#6
You don't want to keep throwing parts at it especially if they're used and you don't know if they're working right. You'll need a multi-meter to check everything out.


P0500 – Vehicle Speed Sensor Malfunction
• Open or short in speed sensor circuit
• Vehicle speed sensor malfunction
Instrument cluster malfunction
• PCM malfunction

P0720 Output Speed Sensor Circuit Malfunction
 

2POINTautO

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#7
Is this a three wire hall effect type sensor. From there, it goes to the speedometer module where it is converted to a digital square wave for use by the ECM/TCM and the cruise modules. Do you have cruise and does it work with no reading on the speedo. Do all the tests including the use of a lab scope to watch the speed signal to the ECM. With that also use a scan tool to watch the speed pid on the data stream. However, the ECM speed pid would drop to zero and be very erratic. Of course you can pull the sensors and rotate them by hand and just use a voltmeter as mentioned but I think the other guys want you to hook up to the proper test points and see what is going on, I think you have to drive very slow, higher speed may not show up on a plain multimeter??? (I have a scope).

Look on the back of the speedo head for a white/violet wire, pull the connectors that you feel are involved and clean them good, throughout the speedo system.
 
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#8
Hi Guys
I down loaded a troubleshooting guild it told me to check Sp1 and e1 on the ECm it said it should be 5v with the cruise ECU disconnected and the key to the on position. it came up 2.25 volts. then I drove the car and the voltage was between .8 and 1.5. I test drove it some more on the same road and same speed it jump up to 2.25 volts and he car shifted OK. I press the power button on the transmission and the meter jumped to 12 volts. When I drove the car the meter went down to 5 to 6 volts. I press it again and it down to .8 and never came back up and the car did not shift correctly it does shift fine in the power mode .Can only one part of the computer go bad.(On the drive home I used the cruise and it worked fine the speedometer was OK too.) One more thing while testing Sp1 to E1. I inch the car slowly the meter went .9 to 3.5volts before the test drive. after the test drive (30 minutes) I checked again .9 to 1.5 volts. and with the power button on .9 to 12 volts.
 

2POINTautO

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#10
A better understanding of the system is needed I think. I know I am putting this simply, VSS sends a signal to the speedo head, this may be an analog signal, the speedo head then digitizes the signal and sends it out to all the computers.

I do not know if a digital signal runs the speedo, it may, if it is not digitized properly, the computers will not operate the system properly.

The system runs on a 0 (off) 5 volt (on) signal, your meter may not be the best test equipment while driving, its to slow and it may be averaging the signal to about 2.25 volts??? I do notice you got 2.25 while not driving.

I have seen where the speedo was effected by the odometer only.
 

csaxon

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#11
Does your speedometer still jump around when you start the car? Did you find this VSS2

Verify you have the 541 and not the 540 trans.
 
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#12
hi guys
I do have the NC2 or vss2 speed sensor. I removed the vss1 speed sensor and checked at the back of the speedometer. I had 12 volts as I turned the speed sensor vss1. I ohmed the connection from the speedometer to the plug on the ecm (sp1) about 6 ohms. I checked the voltage at sp1 to e1 on the ecm but at best i got 2 volts. That was by pushing the car and looking at the meter.(very ,very slowly).I also ohmed out the NC2speed sensor 600 ohms looks OK. Not sure what to do next.
 
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#13
hi guys
When I measured vss1 I got 0 to 12 volts as I turned the speed sensor by hand.
 

csaxon

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#14
Hello again. It looks like VSS1 is ok. Your 1st post indicated a jumping speedometer, has that stopped since replacing the instrument cluster?
By the way you don't have to push the car. Just raise the left wheel and support the car with a jack and spin the wheel. Leave the other wheel down.
VSS2 with the wheel spin should indicate between 0 and infinity ohms. Try the magnetic test also.
 

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#15
Do you still have a check engine light? Can you re-scan to confirm any new or old error codes?