HELP! Overdrive kicking off
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HELP! Overdrive kicking off
1998 Dakota with a 5.2, not sure which transmission. I've had it a week. The check engine light was on and showed a speed sensor fault. I replaced both speed sensors and it eliminated the check engine light. I also had the transmission flushed.
Early in the drive, it shifts fine and goes in to overdrive, but once it is driven a few miles, it will automatically drop out of overdrive and it will not go back in until you turn it off and let it sit for a few hours. When the overdrive is working, you can turn the overdrive off and on with the switch in the shifter handle. When the overdrive is not working, turning the switch on and off makes no difference.
Any suggestions are appreciated.
Early in the drive, it shifts fine and goes in to overdrive, but once it is driven a few miles, it will automatically drop out of overdrive and it will not go back in until you turn it off and let it sit for a few hours. When the overdrive is working, you can turn the overdrive off and on with the switch in the shifter handle. When the overdrive is not working, turning the switch on and off makes no difference.
Any suggestions are appreciated.
Champion
Joined: May 2008
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From: Apex, NC
First, you should have the 46re automatic transmission.
Just out of curiosity, has the fluid level been checked since you got it flushed? Usually once flushed, it takes the fluid a while to make it through all the passageways to all the gears and the level could have gone down in the pan. Thats the first thing I would check.
If its not that, the computer takes input from the speed sensor, throttle position sensor, and coolant temp sensor to determine when a shift into overdrive can be made, so it could be one of those.
Just out of curiosity, has the fluid level been checked since you got it flushed? Usually once flushed, it takes the fluid a while to make it through all the passageways to all the gears and the level could have gone down in the pan. Thats the first thing I would check.
If its not that, the computer takes input from the speed sensor, throttle position sensor, and coolant temp sensor to determine when a shift into overdrive can be made, so it could be one of those.
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The fluid level is perfect. I am assuming that the check engine light would come on if one of the other sensors was bad...but maybe not. Where is the temp sensor on the tranny?
(Update: I just found out that my transmission is a 44RE and the dealer parts is not listing a temp sensor)
(Update: I just found out that my transmission is a 44RE and the dealer parts is not listing a temp sensor)
Last edited by cbh; Oct 23, 2009 at 08:26 AM.
Champion
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From: Apex, NC
I meant engine coolant temp sensor, not a transmission fluid temp sensor. The computer won't kick the transmission into overdrive until the engine is up to normal operating temperature. I had my thermostat get stuck open once and the truck ran cold for a couple days and it didn't ever kick it into overdrive... even at 70mph.
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Is it likely that the temperature gauge is reading normal operating temps, but yet the temp sensor still is sending a bad signal that would allow the overdrive not to work correctly? Also, would the same be true with the TPS? I'm having no problem with throttle or idle.
Champion
Joined: May 2008
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From: Apex, NC
If the gauge reads normal, it's probably not the ECT sensor. On my '95, there are 2 ECT sensors... one for the computer and one for the gauge, but you should only have one that feed the computer which feeds the gauge. It could still potentially be the TPS, but it's weird how it works fine and then doesn't. Usually bad sensors aren't consistently inconsistent (if that makes any sense at all).
It could be that the overdrive unit is starting to fail
They are one of the weakest points to these transmissions. I'm at a loss though and out of ideas. Hopefully someone else can shed some light on this.
**EDIT**
Here is what the '01 FSM says about the 3-4 shift:
apply pressure acts against the overdrive piston.
The '95 FSM for the 46rh lists those "various sensor inputs" as the ECT, TPS, and speed sensor... i assume it is the same for the 46re.
It could be that the overdrive unit is starting to fail
They are one of the weakest points to these transmissions. I'm at a loss though and out of ideas. Hopefully someone else can shed some light on this.**EDIT**
Here is what the '01 FSM says about the 3-4 shift:
FOURTH GEAR POWERFLOW
Fourth gear overdrive range is electronically controlled
and hydraulically activated. Various sensor
inputs are supplied to the powertrain control module
to operate the overdrive solenoid on the valve body.
The solenoid contains a check ball that opens and
closes a vent port in the 3-4 shift valve feed passage.
The overdrive solenoid (and check ball) are not energized
in first, second, third, or reverse gear. The vent
port remains open, diverting line pressure from the
2-3 shift valve away from the 3-4 shift valve. The
overdrive control switch must be in the ON position
to transmit overdrive status to the PCM. A 3-4
upshift occurs only when the overdrive solenoid is
energized by the PCM. The PCM energizes the overdrive
solenoid during the 3-4 upshift. This causes the
solenoid check ball to close the vent port allowing
line pressure from the 2-3 shift valve to act directly
on the 3-4 upshift valve. Line pressure on the 3-4
shift valve overcomes valve spring pressure moving
the valve to the upshift position. This action exposes
the feed passages to the 3-4 timing valve, 3-4 quick
fill valve, 3-4 accumulator, and ultimately to the
overdrive piston. Line pressure through the timing
valve moves the overdrive piston into contact with
the overdrive clutch. The direct clutch is disengaged
before the overdrive clutch is engaged. The boost
valve provides increased fluid apply pressure to the
overdrive clutch during 3-4 upshifts, and when accelerating
in fourth gear. The 3-4 accumulator cushions
overdrive clutch engagement to smooth 3-4 upshifts.
The accumulator is charged at the same time as
Fourth gear overdrive range is electronically controlled
and hydraulically activated. Various sensor
inputs are supplied to the powertrain control module
to operate the overdrive solenoid on the valve body.
The solenoid contains a check ball that opens and
closes a vent port in the 3-4 shift valve feed passage.
The overdrive solenoid (and check ball) are not energized
in first, second, third, or reverse gear. The vent
port remains open, diverting line pressure from the
2-3 shift valve away from the 3-4 shift valve. The
overdrive control switch must be in the ON position
to transmit overdrive status to the PCM. A 3-4
upshift occurs only when the overdrive solenoid is
energized by the PCM. The PCM energizes the overdrive
solenoid during the 3-4 upshift. This causes the
solenoid check ball to close the vent port allowing
line pressure from the 2-3 shift valve to act directly
on the 3-4 upshift valve. Line pressure on the 3-4
shift valve overcomes valve spring pressure moving
the valve to the upshift position. This action exposes
the feed passages to the 3-4 timing valve, 3-4 quick
fill valve, 3-4 accumulator, and ultimately to the
overdrive piston. Line pressure through the timing
valve moves the overdrive piston into contact with
the overdrive clutch. The direct clutch is disengaged
before the overdrive clutch is engaged. The boost
valve provides increased fluid apply pressure to the
overdrive clutch during 3-4 upshifts, and when accelerating
in fourth gear. The 3-4 accumulator cushions
overdrive clutch engagement to smooth 3-4 upshifts.
The accumulator is charged at the same time as
apply pressure acts against the overdrive piston.
Last edited by 95_318SLT; Oct 24, 2009 at 01:26 AM.
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Well.........it wasn't the TPS! I changed it out this morning and it made no difference. I'm going to change the transmission filter later today. It probably won't cure the problem, but I'm sure that it needs done anyway.
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Champion
Joined: May 2008
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From: Apex, NC
Lol, there you have it! A little late to show up but hopefully it will fix your issue. Too bad you already pulled the pan and changed the filter, cause that shift solenoid is on the valve body... above the filter :P