How exactly did you guys rule out wiring? Measured at the ECM connector to make sure that you were seeing the proper resistance?
5-speed A750 trans won't shift in to 5th gear. (5 Viewers)
- Thread starter MongooseGA
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
How exactly did you guys rule out wiring? Measured at the ECM connector to make sure that you were seeing the proper resistance?
And were able to grt a reading of 11-15 Ohms across the solenoid coil? Hmm.
Last edited:
- Thread starter
- #144
Well, I'm questioning myself now. Maybe my meter isn't that kind of smart, we read resistance at '1' for those tests. To imply, as I understand it, that there was continuity through the whole wire.
Also the FSM page numbers that you posted don't jive with the page numbers in what I just downloaded. Trippy.
awesomeissquid
SILVER Star
Sounds correct. Continuity of "1" is just saying that the meter could send an electrical signal from one end of the wire to the other. The resistance of 11-25 Ohms across the wire is needed because the ECM is expecting a certain signal strength/pattern to control correctly. If the resistance is too high (usually due to corrosion) the ECM could be throwing the code and preventing the shift from occurring.
My FSM is for a 2003, but I assume the wiring is the same. That's an assumption though, so if you have a 2005 PDF double check the pinout on the connector.
You need to check the actual resistance. A solenoid is nothing but a whole bunch of turns of wire - when you run enough current through it, the resultant electric field creates a magnetic field. It needs to have a measureable resistance.
If the resistance is lower than that spec, then that means there's a short in one of the wraps. If it's higher, that means it may not be able to generate the needed current to actuate the solenoid.
Your ECM is limited in the voltage it can output by whatever battery/alternator voltage is. Ohms law being what it is (Voltage = Resistance*Current, so Current =Voltage/Resistance), that means if you have a high resistance, your current goes down. Current is what creates the electromagnetic field that makes a solenoid work.
Last edited:
- Thread starter
- #147
Ah, so I made the same mistake that the shop did. Noted. Now I know what's being tested though so I can do it again.
Also, a correction/clarification to an earlier post- I've replaced the No1 speed sensor, not the others (NT and SP2) shown below.
Just getting back to this. The major difference is the ratio of gang-related crime incidents-to-corn fields is inverted.
- Thread starter
- #150
Just getting back to this. The major difference is the ratio of gang-related crime incidents-to-corn fields is inverted.
Fair point, sir! I am looking for someone local. Unfortunately, all my local 100 buddies have older or new trucks
If anyone reading has an early build 2005 model with an ECM part number ending in C40, and you don't need your truck for like a week, and you like bourbon... hit me up.
Ugh, I wish you were closer yet again. My 2005 was built in late 2004, and my truck will be out of commission once I pull my diffs to rebuild them here in the next couple of weeks.
I am looking for someone local. Unfortunately, all my local 100 buddies have older or new trucks
If anyone reading has an early build 2005 model with an ECM part number ending in C40, and you don't need your truck for like a week, and you like bourbon... hit me up.
- Thread starter
- #152
Hmm...
I also put a call in to a local indy I've used a bunch who specializes in Toyotas. He's got an old tech who is an electrical wizard. If they can get the truck in quickly, I may just have him look through it. I don't have the time or focus for this project unfortunately, and I can only rope my friends in for assistance but so much.
Edit: Well, turns out that old tech died from cancer last year.
Last edited:
2001LC
SILVER Star
Throwing darts here, hoping to hit something that rings a bell:
This is a head scratcher for sure. When I've gotten into them, when dealing with electronic signal. It's been issue of resistance. Either ground fault, wire housing block issue or frayed wires. Many faults have been due to water entry, either into cabin via windshield or into wire housing blocks found under the body (undercarriage). Frayed wire faults are mostly from rodent chew or rub due to improper routing. Incase of wheel speed sensor on built rig, often wire gets damaged from being screeched.
It's a long thread. I do recall the P0771 DTC does return after cleared, and mention of "some" wheel speed sensor (WSS) seen but did not return. But not which WSS DTC. I doubt WSS is an issue here with AT shifting to 5th. Those WSS DTC (4 of them), point to which WSS of the 4. Why in another thread, he found bad WSS without a DTC, is unusual. All bad WSS I've seen, do kick off a DTC and shuts down ABS. So we get warning lights on dash.
I've yet to find a cause and effect in FSM between AT & WSS. But perhaps I need to look deeper!
Looking at some diagnostic in FSM for P0771. It starts with many of which swapping AT would or should have taken care of. That and test of the various sensor & solenoids, your shop and you did.
All to often FSM tree, points to EMC or some CPU. When the issue, is resistance in wiring, not a controlling computer.
Some of sensory input to EMC controlling AT, that are not in AT. Like ECT sensor and "KCS" sensor circuit. I'm not sure what KCS is. But since it mention Spark Advance. This may be, a knock sensor. Anyone know?
Anyway, it need to see a 0 percent "CA" or more. Again, I'm not sure what FSM saying with "CA". But I assume crank angle of zero or more. So this would be read by crank position sensor (CPS). Could a damage wire of crank sensor, have a fault, and not set off a DTC. Perhaps. I'd certainly check the wire to CPS. So many routed wrong during T-belt and or fan bracket service, and the wire rub serp belt and get cut. Sometimes only part way through wire strands. Thus changing resistance, yet we see continuity. That wire, many have later been routed correctly behind fan bracket, out of sight. I'd inspect, just to rule out.
Also FSM states, "transfer range be in high". It's unusual to replace a TC, but IIRC, you have. So I'd be looking at it's switches, wires and their wire housing block also.
With deep dive, we find. EMC also uses other signals. Such as EMC gear position. Also throttle valve opening angle. Again this should kick off it's own DTC. But perhaps did not.
Digger deeper the lock-out uses MAF, crank position sensor, brakes and a few others. Any of which "should" kick off a DTC. Lock-out, may be unrelated to overdrive/5th, I'm not sure?
But if lock-out does effect 5th
One input, that would not likely set off a DTC. Is, if brake pedal pushed slightly. Which when pushed, release the brake light switch (brake tail lights come on) A loose switch may act the same. This one easy test,. Are brake light working normally.
Hang in there!
This is a head scratcher for sure. When I've gotten into them, when dealing with electronic signal. It's been issue of resistance. Either ground fault, wire housing block issue or frayed wires. Many faults have been due to water entry, either into cabin via windshield or into wire housing blocks found under the body (undercarriage). Frayed wire faults are mostly from rodent chew or rub due to improper routing. Incase of wheel speed sensor on built rig, often wire gets damaged from being screeched.
It's a long thread. I do recall the P0771 DTC does return after cleared, and mention of "some" wheel speed sensor (WSS) seen but did not return. But not which WSS DTC. I doubt WSS is an issue here with AT shifting to 5th. Those WSS DTC (4 of them), point to which WSS of the 4. Why in another thread, he found bad WSS without a DTC, is unusual. All bad WSS I've seen, do kick off a DTC and shuts down ABS. So we get warning lights on dash.
I've yet to find a cause and effect in FSM between AT & WSS. But perhaps I need to look deeper!
Looking at some diagnostic in FSM for P0771. It starts with many of which swapping AT would or should have taken care of. That and test of the various sensor & solenoids, your shop and you did.
All to often FSM tree, points to EMC or some CPU. When the issue, is resistance in wiring, not a controlling computer.
Some of sensory input to EMC controlling AT, that are not in AT. Like ECT sensor and "KCS" sensor circuit. I'm not sure what KCS is. But since it mention Spark Advance. This may be, a knock sensor. Anyone know?
Anyway, it need to see a 0 percent "CA" or more. Again, I'm not sure what FSM saying with "CA". But I assume crank angle of zero or more. So this would be read by crank position sensor (CPS). Could a damage wire of crank sensor, have a fault, and not set off a DTC. Perhaps. I'd certainly check the wire to CPS. So many routed wrong during T-belt and or fan bracket service, and the wire rub serp belt and get cut. Sometimes only part way through wire strands. Thus changing resistance, yet we see continuity. That wire, many have later been routed correctly behind fan bracket, out of sight. I'd inspect, just to rule out.
Also FSM states, "transfer range be in high". It's unusual to replace a TC, but IIRC, you have. So I'd be looking at it's switches, wires and their wire housing block also.
With deep dive, we find. EMC also uses other signals. Such as EMC gear position. Also throttle valve opening angle. Again this should kick off it's own DTC. But perhaps did not.
Digger deeper the lock-out uses MAF, crank position sensor, brakes and a few others. Any of which "should" kick off a DTC. Lock-out, may be unrelated to overdrive/5th, I'm not sure?
But if lock-out does effect 5th
One input, that would not likely set off a DTC. Is, if brake pedal pushed slightly. Which when pushed, release the brake light switch (brake tail lights come on) A loose switch may act the same. This one easy test,. Are brake light working normally.
Hang in there!
What a PITA you're going through!
I don't have much to add, but just a question.
Did you try to disconnect your ScanGauge from your OBD port while testing?
The reason I suggest is bc I had an OBD dongle to run Fusion app, and the LC was behaving weird at startup, took me a while to figure it and all went back to normal when I took it off.
Since then I got me a SG and all is good, but maybe yours isn't..
Just a suggestion that's easy enough to try.
Good luck with your LC, also have a 2005 and hate to even think about trans issues.
I don't have much to add, but just a question.
Did you try to disconnect your ScanGauge from your OBD port while testing?
The reason I suggest is bc I had an OBD dongle to run Fusion app, and the LC was behaving weird at startup, took me a while to figure it and all went back to normal when I took it off.
Since then I got me a SG and all is good, but maybe yours isn't..
Just a suggestion that's easy enough to try.
Good luck with your LC, also have a 2005 and hate to even think about trans issues.
- Thread starter
- #155
WSS was the RH rear. I visually inspected mine this morning and compared to the other thread where dude replaced his and fixed trans issues, mine looks to be in great shape. No obvious signs of breakage.
Transfer case has been removed/regeared, but not replaced. Other than the transmission swap, the case hasn't been out in 10s of thousands of miles.
Honestly, I'm feeling pretty defeated and this is over my head for my current skills.
Good question. I don't recall exactly, as I may have had the SG removed when we tested in case I needed to hook up TS. I did drive the truck with the SG disconnected, and the issues are still present.
@Wermz and I are gonna try some more testing next week.
Just putting it out there again, if anyone has an early build 2005 (up to 4/05 build date), I'm more than happy to trade you a bottle of your favorite liquor for a day to borrow your ECM.
If you were closer I’d let you pull mine to check. It’s my daily thought so I can’t pull it and ship it. Good luck. I’ve really gotten invested into this fix. The closest I ever get to ATL anymore is still 5 hours away.
2001LC
SILVER Star
I doubt WSS has anything to do with your AT issue anyway. FWIW; Rarely is there visible signs a WSS is bad. Most WSS I've replaced. Indications were, the wire had been stretched. Which damaged wire, changing resistance. All had current DTC, clear and DTC would come right back.
Last edited:
- Thread starter
- #158
I sent my ECM and a bottle of Atlanta's finest out to @LJE this morning to test against his truck. Thank you for this!
For those looking in to potential ECM issues, the later model trucks can have a same-part-number ECM, even used, swapped in without dealership programming. You use a jumper wire to connect pins 4 and 13 on the OBD port under the dash and leave the key on for 30 minutes. This "handshake" programs the immobilizer in later vehicles and will allow you to drive the vehicle with the 'outside' ECM installed. This same process (and same pins 4/13) also works on myriad other Toyotas of the same era.
For those looking in to potential ECM issues, the later model trucks can have a same-part-number ECM, even used, swapped in without dealership programming. You use a jumper wire to connect pins 4 and 13 on the OBD port under the dash and leave the key on for 30 minutes. This "handshake" programs the immobilizer in later vehicles and will allow you to drive the vehicle with the 'outside' ECM installed. This same process (and same pins 4/13) also works on myriad other Toyotas of the same era.
Should be here Saturday! I expect my LX to have a southern accent once I drop your ECM in.
