4l65e - P0740 - But doesn't make sense to me.
08-31-2015, 08:54 PM
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4l65e - P0740 - But doesn't make sense to me. Recently re-worked my harness (finally deleted everything I don't need) on my 05 lm7/4l65e in my 98 XJ a few weeks ago. No issues.
Was out wheelin' last night and towed a truck out of the trail, but doubt that's related. Rain has finally started, and I'm guessing I've got an intermittent electrical issue caused by the water.
Driving to store today (highway) and threw a p0740. Immediately after, I noticed that trans was shifting strange. On accel, shifting up way to early, and not shifting down when it should. Manually changing gears everything works fine. At a slow idle/cruise in traffic, it was dropping all the way to 4th (while doing about 25km/h), and when I hit the gas, it just lugs and lugs at 800RPM or so unless I stomp on it, in which case it shifts way down and Jeepy moves along nicely. Watching my TCC slip RPM, it looks like the TCC is locked up all the time, but when I slow down to stop, TCC slip increases as normal and I don't stall out.
On the way home, I pulled the relay that fires the brake signal over to the PCM, and sure enough, everything runs perfect. All my shifts are smooth and correctly timed, I just don't get any TCC lockup at highways speeds.
So all this said, I'm not at all sure the TCC was locking up. All I know is the reported TCC slip was near 0 while moving around at low speed, hit the gas and it doesn't rise and the trans is trying to accelerate me at 25km/h at 1000RPM instead of gearing down or allowing the TCC to slip to increase RPM. No stall, so TCC isn't stuck locked, and remove the Brake switch relay and problem goes away.
What'd ya'll think? I can't imagine this being a mechanical issue at this point, but I don't really fully understand how and when the TCC works. I understand it's purpose and intended operation just fine, but I don't know the low level stuff like whether the TCC valve opens to lock the TCC or the other way around.
Was out wheelin' last night and towed a truck out of the trail, but doubt that's related. Rain has finally started, and I'm guessing I've got an intermittent electrical issue caused by the water.
Driving to store today (highway) and threw a p0740. Immediately after, I noticed that trans was shifting strange. On accel, shifting up way to early, and not shifting down when it should. Manually changing gears everything works fine. At a slow idle/cruise in traffic, it was dropping all the way to 4th (while doing about 25km/h), and when I hit the gas, it just lugs and lugs at 800RPM or so unless I stomp on it, in which case it shifts way down and Jeepy moves along nicely. Watching my TCC slip RPM, it looks like the TCC is locked up all the time, but when I slow down to stop, TCC slip increases as normal and I don't stall out.
On the way home, I pulled the relay that fires the brake signal over to the PCM, and sure enough, everything runs perfect. All my shifts are smooth and correctly timed, I just don't get any TCC lockup at highways speeds.
So all this said, I'm not at all sure the TCC was locking up. All I know is the reported TCC slip was near 0 while moving around at low speed, hit the gas and it doesn't rise and the trans is trying to accelerate me at 25km/h at 1000RPM instead of gearing down or allowing the TCC to slip to increase RPM. No stall, so TCC isn't stuck locked, and remove the Brake switch relay and problem goes away.
What'd ya'll think? I can't imagine this being a mechanical issue at this point, but I don't really fully understand how and when the TCC works. I understand it's purpose and intended operation just fine, but I don't know the low level stuff like whether the TCC valve opens to lock the TCC or the other way around.
09-02-2015, 08:53 AM
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Perhaps some water got into the trans connector?
I haven't heard that a p0740 code would cause early upshifts, but I don't know much about this code.
"shifting up way to early" often indicates an engine sensor problem, but perhaps not this time.
Remember the trans does not shift by itself; all shift commands come from the PCM.
I would check for a bad connection to maybe the TPS or MAF.
Also, I assume the speedometer is accurate and steady.
I doubt anything serious is wrong with the trans; worst case the TCC solenoids are trivial to replace.
I haven't heard that a p0740 code would cause early upshifts, but I don't know much about this code.
"shifting up way to early" often indicates an engine sensor problem, but perhaps not this time.
Remember the trans does not shift by itself; all shift commands come from the PCM.
I would check for a bad connection to maybe the TPS or MAF.
Also, I assume the speedometer is accurate and steady.
I doubt anything serious is wrong with the trans; worst case the TCC solenoids are trivial to replace.
12-26-2015, 02:52 PM
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Well crap. I forgot about this thread and didn't get an email notification.
So anyhow, I confirmed that the TCC lockup was somehow shorted to ground, either at the ECU harness connector, on internally in the ECU. After unplugging and replugging and cleaning the **** outta the ECU connector, the ground short disappeared and everything went back to normal.
But, a week later or so, I lost 4th gear for about a minute, then I threw a P1810, then 4th came back but with early shifts and ECU commanded gear has almost no affect on the ACTUAL gear I'm in. I think you're mistaken about the ECM being the only driver of the gear because if you disconnect the trans harness, the trans still shifts, it just uses a higher line pressure.
Anyhow, I found a diagnostic guide (300 pages) for the 4l60e, but can't find one for the 4l65e and I suspect there are a few differences with regards to the electronics.
I was testing my range selector and none of the patterns I saw on my ohm-meter matched the guide for the 4l65e, but they all did sorta make sense. Same with the manifold pressure switch outputs. They all switch, but none of the switch patterns matches the book. This fucked me up for most of yesterday until I realized I was looking at 4l60e specifications.
So at this point, if I clear the P1810, I get 1,2,3. If I put it in 1st, it still shifts all the way up to 3rd. Same with 2,3,4 range selections. Once the P1810 gets thrown again, I get 4th and lockup, but my TCC slip speed is -700rpm while engine RPM is at 2000 at 100km/h. That speed and engine RPM is what it should be for my gearing, but the TCC slip RPM should be 0. -700 is exactly what it would read if the ECU thought we were actually in 3rd gear, so I suspect what's happening is that the ECU is commanding 4th (I wired up some LED's so I can verify the ECU's commanded gear), but THINKS the trans is only in 3rd when it's actually in 4th. This explains the discrepancy with the TCC slip rpm.
That said though, I'm still at a loss. I've been looking at this from an external wiring perspective, but I can't find anything WRONG with the harness (though I'm a little in the dark because I don't know the shift/signal patterns for the 4l65e). P1810 is thrown when the pressure manifold switch is throwing impossible combinations, or throwing a combination that doesn't make sense for the trans speed/engine speed/gear ratio.
I hate just throwing parts at a problem. Especially this time because I'm not 100% confident that I don't have a simple wiring problem, or a bad ECU. The problem MAY be the pressure manifold switch as indicated, but that's a lot of work to replace, only to find out later that the ECU or harness was at fault.
Suggestions?
P.S. When I clear the code, I get a D3 pattern but shifting is exactly where I expect it to be. Just no 4th or lockup. Once the code is set, I get D2 line pressure and D4 shift pattern, and very early shifting, but all gears do work. When I'm in 4th at 100km/h, I can forcibly downshift to 3rd and 2nd, but not 1st. But, if I put the selector in 1,2 or 3, it just shifts all the way up to 4th on it's own. Seems strange to me that the D4 pattern is only forced while shifting up, but I can manually override on the way back down (except to first).
Someone out there knows exactly what the problem is and I'm losing my mind
.
So anyhow, I confirmed that the TCC lockup was somehow shorted to ground, either at the ECU harness connector, on internally in the ECU. After unplugging and replugging and cleaning the **** outta the ECU connector, the ground short disappeared and everything went back to normal.
But, a week later or so, I lost 4th gear for about a minute, then I threw a P1810, then 4th came back but with early shifts and ECU commanded gear has almost no affect on the ACTUAL gear I'm in. I think you're mistaken about the ECM being the only driver of the gear because if you disconnect the trans harness, the trans still shifts, it just uses a higher line pressure.
Anyhow, I found a diagnostic guide (300 pages) for the 4l60e, but can't find one for the 4l65e and I suspect there are a few differences with regards to the electronics.
I was testing my range selector and none of the patterns I saw on my ohm-meter matched the guide for the 4l65e, but they all did sorta make sense. Same with the manifold pressure switch outputs. They all switch, but none of the switch patterns matches the book. This fucked me up for most of yesterday until I realized I was looking at 4l60e specifications.
So at this point, if I clear the P1810, I get 1,2,3. If I put it in 1st, it still shifts all the way up to 3rd. Same with 2,3,4 range selections. Once the P1810 gets thrown again, I get 4th and lockup, but my TCC slip speed is -700rpm while engine RPM is at 2000 at 100km/h. That speed and engine RPM is what it should be for my gearing, but the TCC slip RPM should be 0. -700 is exactly what it would read if the ECU thought we were actually in 3rd gear, so I suspect what's happening is that the ECU is commanding 4th (I wired up some LED's so I can verify the ECU's commanded gear), but THINKS the trans is only in 3rd when it's actually in 4th. This explains the discrepancy with the TCC slip rpm.
That said though, I'm still at a loss. I've been looking at this from an external wiring perspective, but I can't find anything WRONG with the harness (though I'm a little in the dark because I don't know the shift/signal patterns for the 4l65e). P1810 is thrown when the pressure manifold switch is throwing impossible combinations, or throwing a combination that doesn't make sense for the trans speed/engine speed/gear ratio.
I hate just throwing parts at a problem. Especially this time because I'm not 100% confident that I don't have a simple wiring problem, or a bad ECU. The problem MAY be the pressure manifold switch as indicated, but that's a lot of work to replace, only to find out later that the ECU or harness was at fault.
Suggestions?
P.S. When I clear the code, I get a D3 pattern but shifting is exactly where I expect it to be. Just no 4th or lockup. Once the code is set, I get D2 line pressure and D4 shift pattern, and very early shifting, but all gears do work. When I'm in 4th at 100km/h, I can forcibly downshift to 3rd and 2nd, but not 1st. But, if I put the selector in 1,2 or 3, it just shifts all the way up to 4th on it's own. Seems strange to me that the D4 pattern is only forced while shifting up, but I can manually override on the way back down (except to first).
Someone out there knows exactly what the problem is and I'm losing my mind
. 
12-26-2015, 10:34 PM
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Got it figured. What was ******* me up was that all the service manuals I found all had the trans connector backward (correct for the 4l80 but always mirrored on the 4l60/5). Once I figured that out, everything made sense except two wires, which had a break. Problem solved.
12-28-2015, 05:21 PM
#6
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However, glad to hear you figured it out and got it working.