P0500 and P0725 Speed Sensor ??

[Roynotlikecodes]

Okay Guys, this is my first post....I have a 94 V6 Camry auto that is slipping in and out of gear while driving down the highway and recently the OD sometimes won't stay in. The check engine light is on and the OD light will flash when car is acting up (most of the time it flashes, sometimes not) I pulled codes and it shows both speed sensors on tranny. I pulled some used ones and replaced both of them and the problem persists. I've pulled all connections on sensors and the ECM under the dash and cleaned all with electrical cleaner. I've checked for bad terminals, etc. I can't find anything out of place. The trans fluid is still red and the car runs and drives perfect until it acts up. So, I'm pretty well convinced the tranny has no internal damage, just something causing it to act funny intermittently. The car will literally go into neutral while driving and just freewheel and then I let off gas and it will go back into gear for awhile (sometimes for a long while, sometimes for short while) sometimes I can go for days with not one ounce of trouble. Some days it acts up instantly and will persist several times in one trip. Any Ideas?? Thanks

[csaxon]

The ecu doesn't know what gear to be in if the speed sensors aren't providing accurate info. If the sensors have been tested and the gear is not worn or missing teeth and the magnetic pick up isn't broken, then the ecu may be defective.
You can try unplugging the connection to the shift solenoids and cleaning it. It may be loose or corrodid; but I suspect a speed sensor.

The ECU needs input from a water temp sensor, the #2 vehicle speed sensor and the throttle position sensor. These determine the shift points.

[Roynotlikecodes]

Thanks for the reply...I read another post earlier where a guy pulled his instrument cluster and cleaned the connections there. Do you think that's worth looking at. I'm tending to lean towards the VSS with the gear on it because the one I put in seems to be worse, I put the old one back in and it seems to not act up as much, but it still does the same thing. Do you think I can jumper across on the Temp Control unit and trick the car into thinking it is plenty hot to eliminate that variable? Thanks

[88 LE]

Originally Posted by Roynotlikecodes

Do you think I can jumper across on the Temp Control unit and trick the car into thinking it is plenty hot to eliminate that variable?

Did you mean to say water temp sensor? If so its not a good idea to jumper across it.

Water temp sensor changes resistance based on temperature. The resistance goes up or down depending on the type of sensor (PTC or NTC).

NTC = negative temperature coefficient. Resistance goes down as temperature goes up.
PTC = positive temperature coefficient. Resistance goes up as temperture goes up.

ECM uses the water temp sensor for fuel and ignition. So if you jumper across the sensor the ECM is going to think the engine is running to hot or cold (depends on type of sensor) and adjust the fuel and ignition accordingly, even though the conditions are wrong.



What you can do is check the resistance of the water temp sensor vs. temperature with a DMM. Use the specs from a repair manual.

[fenixus]

as far as I know, all Toyotas I've seen so far (mostly gen4 based though) are using "NTC" sensor where resistance drops when temperature grows.

also, to cheat ECU into seeing a stable warm temperature I used in past the resistor of around 230 ohm, that's what the sensor gives out anyways at normal operating conditions (when cold it can say something around 5Kohm around 40-50F or so).

just buy some resistors from radioshack, unplug the ECT and plug the resistor into the socket/plug (car/ECU end) to make it see a stable warm reading on this one.

use contactless digital thermometer (e.g. from Harbor Freight Tools stores) to check the actual coolant temperature based upon rubber hose. as far as I remember the 1mz-fe engine has the thermostat on the passenger side where the lower radiator hose plugs into, so check the temperature at the upper radiator hose. or check both and compare.

I usually replace Engine Coolant Temperature sensors as part of major tune up along with oxygen/AFR sensors at same time. old ECT sensors can misbehave at certain temp/resistance ranges while still giving correct readings at others.

since you have P0500 code, I would check/replace the VSS (vehicle speed sensor) first, it sits on top of transmission (differential body), it's plug is bolted to the body (10mm hex head bolt).

replacing the ECU is usually the LAST step, even though the FSM will suggest replacing it in early troubleshooting often. those things very rarely go bad, trust me, I've been there. in most cases it's the wiring at fault however.

[Roynotlikecodes]

Okay, I know this will make some of you laugh, but here it goes....I was having major problems today with car slipping in and out of gear, would actually roll to almost dead stop before it would finally pop back in and then i was good for awhile and then all over again. So, I unplugged the output speed sensor just to see what would happen, and it would still drive but would not shift out of first. So I pugged it back in and then uplugged the other speed sensor (the one on top of tranny with only two wires) and now the car drives fine. I drove it around several places today and the only think i noticed is the shifting points are a little quicker and the the OD light is flashing. But, the OD works perfect and the car is driving very nice. So, I'm assuming I need to replace the two wire speed sensor?? Any thoughts on this?