hello everybody, suddenly, my camry will go only in reverse. I am doing a lot of testing now, checked solenoids, they are good. I got a lot of manuals and I am doing ECM testing. I have a question:
If it says measure voltage beween terminals of ECM connector, how do you measure it? I know, it might sounds stupid, I am an electrical engineer, but it doesn't make any sense to me. If I want to measure voltage (or even resistance) on ECM, I have to unplug the harness. When nothing is connected to ECM, how I am suppose to test sensors, switches etc? When no harness is connected to ECM, how I can get appropriate reading???

 

I know there is a tool for that...just can't remember what it is.

 

What engine, V6 or 4 cylinder? This makes a difference as to trans type.

You would be measuring the voltage output and resistance of the computer terminals for the computer.

Toyota does have specs to test sensors and solenoids directly at the plug of each item. If there might be a wiring problem, the sensor specs would be checked at the ECM plug.

The computer is just a controller for a piece of equipment. When sensors combined with programing state turn on switch A (a trans solenoid) the computer outputs a high signal (battery voltage something like 9-14V), if not it outputs a low signal (say 0-2 volts).

 

[quote=toyomoho;63979]What engine, V6 or 4 cylinder? This makes a difference as to trans type.

Thanks for your reply. It's 4 cylinder, engine 5S-FE. I totally understand that I can measure resistance directly on solenoids, etc. But to measure voltage on the computer, I cannot unplug all wires/harness, because if nothing is going in, nothing will go out, am I correct? I would need a "bridge", which would allow me access voltage between the computer and plugged harness.

 

OK, if you unplug the cable, the computer will be dead. Thinking of some other car.

Make sure the shift lever on the trans has full travel. When selecting the gear position make sure the trans lever actually moves into a forward drive gear position.

If all OK here, the trans can be operated manually using the gear selector.

Unplug the computer. Attempt to drive the gear using manually selected gears.

If the car still moves in reverse but not forward when you manually put the gear into the 1st there is most likely is an internal problem with the trans mechanisms.

Guessing either the forward clutch or O/D one way clutch. These clutches are not used in reverse operation.

To access there parts requires taking the trans apart.

 

Thank you Joey for your replies.
Basically I am trying to rule out if issues are mechanical or electrical. I did drain the ATF and refill full 2.6 qts. No burned smell, no shavings on magnets. Checked solenoid 1 and 2, both clicks on 9V battery and I got 13 ohms on both. Park/Neutral switch moves and gears are changing fine. I was not able to test resistance on the park/neutral position switch because of the access, but I got 12V on the harness (not the switch itself) for P, N, R, but not D, 2, and L.

Also, I want to perform manual shifting test (which should show if it's mechanical or electrical) by disconnecting the solenoid connectors behind the P/N switch, but it's really hard to unplug. I was able to disconnect the right connector, but not the left one. I will have to try it again and see what happens. (btw. I hate these connectors!)
I was not able to start the car with computer unpugged, so I don't know how to do the manual test you mentioned. I can probably start the car and then unplug the computer (ECM)?

 

Also, one more thing. I do want to test the Park Neutral Position Switch circuit. It says to check voltage between terminals NSW, 2, L of ECM connector and body ground, but again, I don't know how to measure that, because I do have to unplug the harness to get to pins on ECM, right???

 

Suggest you not disconnect the ECU with ign switch or engine on. Trans ECU and Engine ECU are combined on this year.

Forget what I wrote about disconnecting the plug at the ECU. Suggest you try your best to unplug the computer connection harness at the trans.

Would think if the engine starts in park or neutral but not in a gear this switch would be OK.

Suggest you use a probe to the individual circuit terminals when the plug is installed?

Have never heard of an extension board or breakout box that goes between the ECU and harness plug.

 

Yes Joye, I am going over michell 1 on demand and it does say that you measure voltage backprobe. It does totally make sense! That's why I was wondering why some say that you disconnect the harness and then measure the voltage. You have to backprobe it!

I will be doing more testing, thanks!