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Discussion Starter · #1 ·
My names Garrett,

I have a 1993 k3500 6.5 turbo diesel with 4l80e tranny. Stuck in limp mode and whenever I stop it gets stuck in neutral. If I turn the truck off and back on it'll shift back and stay in limp mode until I stop again. Same when shifting into reverse have to turn it off and back on for tranny to shift.

know how to fix the limp mode. any advice on tranny getting stuck in neutral will be greatly appreciated... Thanks
 

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Your truck does not have a limp mode, do what the 2nd post says and go from there.
 

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Diesel Master
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Your truck does not have a limp mode, do what the 2nd post says and go from there.
It is and has been referred as a limp mode. The 4L80E defaults into second gear. Limp mode is short for limp home mode. This term has been used for years in the transmission industry.
Being in the military I have seen many types of transmissions have limp modes. Many manufacturers even term it different. As long as an electronic transmission can drive the vehicle without electrical power but not shift it can be termed as limp mode. IMHO..
 

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Discussion Starter · #5 ·
I was thinking it was the shift linkage but when it gets stuck in neutral if I turn the truck off and back on it will go back into limp mode or stuck in second gear which would mean it has to be a computer control problem correct???
 

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Discussion Starter · #8 ·
Check and make sure your shifting linkage from shifting column is correct and then see if the problem persists.
the linkage looks fine, makes a nice crisp click noise and moves properly to each position.

-Garrett
 

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Diesel Master
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Check out the computer and make sure that the connections are well connected. Ground next to the computer is not corroded. Go to the back of the block and make sure that the back of the block is well grounded. The battery or batteries are well connected and grounded. take a multimeter and set it on Volts DC and measure the batteries for 12 VDC.
the computer should have at least 9 volts going to it even during starting the truck IMHO. anything less then problems.
Make sure if any connections coming off the TPS wiring is well connected. RPM sensor is well connected. These two determine engine load for the computer. TISS and VSS/TOSS Vehicle speed sensor Transmission Speed sensor are well connected. Corrosion to any connector, even to ground causes voltage drop.
Voltage drop is pressure drop within the circuit. Think of Voltage drop like this. Watering your garden. 15 lbs of pressure out of your house but you step on your hose. Now you only have 8 lbs coming out of the hose. That is voltage drop with corrosion at connections, pins, ect..
Electricity has to fight through resistance especialy through connections and grounding points where bolts terminate the ground wire.


The 2-3 shifting solenoid may not be engaging. If you suspect this happening then disconnect the connection going into the transmission. Take a nine volt battery. Solder two leads 8" or so long and disconnect the passthrough connecter. Touch B and E. This is the 2-3 shifting solenoid. You should hear a clicking sound.
This is not total answer because the check ball could be stuck within the 2-3 shifting solenoid Or the shifting solenoid fell out and dropped into the pan. Worse the computer is not controlling the 2-3 shifting solenoid by closing the circuit.
This is by no means a cure all but will point you in the right direction

 

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Diesel Master
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The pressure manifold switch need mentioning big time.
If your 2-3 shifting solenoids check out then you need to check out your pressure manifold switch. this switch contains 5 switches that tells the computer which gear you selected the "told" transmission to be in. the computer expects to "see input and output" speeds relating to the pressure manifold switch "feedback"

The pressure manifold looks like this if you take the pan off.


It has 5 switches. These 5 switches has 3 wires leading into them and ground out into the switches.
Through a combination of these switches the computer detects "feedback" as to which gear you are supposed to be in.

If your Input and output speeds fail the computer's expectation than
you will lock into 2nd.
 

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Diesel Master
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You can check the pressure manifold switch using resistance through a multimeter and the drive ranges. Look at the middle of the illustration and note the Pass-thru Terminal This is what you read at the connection at your transmission. Using the chart below H equals 200 Ohms and L equals 100 Ohms or less.
Place the transmission into Park N should read 200 OHMS resistance between Pin N and ground. Just for the park range.
continuing with park. R should read 100 Ohms or less
P should read 200 Ohms or so.
For each you are checking N R P but you are getting different readings that should match the chart.
If they do not match the chart then get another pressure manifold switch.



 

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Discussion Starter · #12 ·
ground wires seem to be fine, I went from the battery to the block and other parts of the engine. I do not know what a lot of the things in the last three messages are or look like. your photobucket pictures say they were moved or deleted.
 

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Diesel Master
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Drop the pan and see if there is debris in the pan. Did the transmission overheat. The answers you need right now are.
Is it electrical?
Is it mechanical?
Heat kills transmissions.
Little problems that you might have had before might have turned into a larger one now.
Just for FYI look at the torque converter. is it discolored from the heat?
 
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