pennda

After 144,000 trouble free miles, I get a P0768 code, without any previous transmission or shifting problems. In April, had new shift solenoid installed along with full transm servicing, new oil (purged) completely checked out. A month later, we make a 1,500 mile trip to east coast - no problems, no engine lights, nothing. About a month later engine light again, with about 11 diff. codes - most dealing with engine tune up, O2 sensor, etc. All engine codes & sensors replaced - finally all codes clear, even after couple of drive cycles. No underlying codes appear after all engine corrections, no engine light, no indication of shift solenoid code.

After a one hour test drive, with NO shifting trouble, engine light appears, with test code of P0768 D shift solenoid!

Is this really a solenoid problem, or electrical wire problem, or computer box problem? How can one isolate this puzzle? Is there a recommended brand solenoid as good or better than Toyota?

Or might this clear up after a battery disconnect? Need expert guidance on this.

Lexmex

I remember you had this before.

The ony things it can be is the ECM, the solenoid or the harness/wire. There is a complex series of steps in volume 1 of the repair manual as far as measuring resistances on the ECM and connectors, which is something I strongly advise one to have if they are going to DIY repairs, as it will help you pinpoint it exactly.

One group you might want to talk to about solenoids is http://www.ipttrans.com but not sure if they can directly help you or not with a part, they're out in Jersey.

Disconnecting the battery will just do it temporarily.

pennda

General interest - when you disconnect the battery, does the system 'log' the disconnect or re-set?

Lexmex

Not that I know of. In fact, the juice is supposed to be out of the capacitors in about 10 seconds, though I usually leave if off for at least a minute.

However, you are going to notice it drivea a bit funny, in terms of acceleration, until the ECM gets enough information from your driving patterns, which won't take too long.

pennda

My mechanic solved all codes, RX ran fine, except now after 200 miles of no engine light, it now strangely re-appears, and another P0768 code! (with no underlying codes) The odd thing is that there is no transmission, shifting or operating problems - all smooth shifting, doesn't miss a beat.

Any ideas out there? Or do I just suck it up and have another shift solenoid replaced? Assuming that is really what it is.

Lexmex

If it were me, I would check the electrical connections/harness/connectors to the tranny, all of them, with battery disconnected. I doubt ECM is the problem, but by deduction after examining these harnesses, likely the solenoid is ok. I called my uncle about this one and he knows of a few people who have driven around with this error (ever since I got him an OBDII scanner about 3 years ago) and not an issue.

Keep in mind, that getting this error doesn't mean its dead, just that it detected a condition that is out of the normal range, otherwise that P0768 would be coming on 24/7 instead of just after 200 miles.

pennda

Thanks so much for your help! Im thinking the same here, too. Transmission is solid with smooth shifts up and down. I have an experienced mechanic, but he has torn his hair out all week on my car. How do you recommend testing the harness? (understand no live battery)

If it is some harness wiring, is it expensive to repair? Or does whole harness need to be replaced or just faulty wires?

pennda

I have also read in other posts, that when doing a battry disconnect, you can hold the 2 battery cables together for about 20 secs to re-set. Is this okay to do? Any harm? But I would suppose another 2-3 drive cycles to double check again?

Lexmex

There is a way of checking resistance, but it is a little too complicated too show here as it is indicated in Volume 1 of the service manual. However, under the circumstances, I would as I mentioned earlier, disconnect battery, disconnect harnesses on the transmission, and then reconnect them. I doubt it is the harnesses themselves and it probably is nothing more than a brief sensor reading off of the solenoid in question, which probably unfortunately needs replacing again.

Lexmex

Not necessary at all, and I would be a bit careful with that as you can get a shock sometimes with some energy still in the system.

pennda

Can metal filings in the tran also be a root cause for out of range sensor readings? Would all of this be an early indicator of trans problems down road?

But I do like your idea of also disconnecting the trans wiring. Who knows, the good transmission gods might chase away the goblins!

Fortunately or unfortunately, I just sold the car a few days ago. But I'm leaning on the right side of honesty and probably will, worst case replace solenoid. And I probly would have a Toyota dealer do repairs, I think.

Ever since I bougth car at 72K miles - it has been a solid performer! But only wine gets better with age?

I do appreciate your help.

Lexmex

Well, main factor I was thinking about is that sometimes when one solenoid is replaced and not the others, sometimes the gremlins can come about in those situations. I know this can occur with O2/Air-Fuel sensors, too. Metal filings aren't unheard of in causing certain tranny issues. Easiest way to check is of course is if your brake fluid is silvery/pinkish. I had this once and got a flush on a trip back to Florida about 4 years ago.

I plan to keep my RX as long as possible...there's still many records I'd like to break.