1991 k3500 7.4 4l80

[Haasbuilt]

My truck is giving me issues it shifts into overdrive just fine but drops back into 3rd and will not go back into overdrive untill restart. Have code 68

 

[MrMarty51]

OBD 1 code 68 has nothing to do with the transmission. AC compressor relay fault. It could be the same circuit might have something to do with controlling the overdrive function.
Usually though, a fault with the overdrive could be related to the coolant temp sensor located near the thermostat housing on the gas powered engines. Most times though, if the ECT sensor is faulty, then the torque convertor lockup will also be disabled.
Count how many times the engine shifts getting above 40 MPH, then, touch the brake pedal, not step on it, just a touch, the engine should gain a couple hundred RPMs when the brake pedal is touched. If You count four shifts, then the OD is probably functioning and the TCC lockup is failed.
Welcome to the forum. Those with more knowledge will most likely come in and post a bunch of stuff I either forgot, or, dont know about.
Unless they is all out camping, fishing, wood cutting or just in he eral goofing off.

 

[Haasbuilt]

View attachment 62118

OBD 1 code 68 has nothing to do with the transmission. AC compressor relay fault. It could be the same circuit might have something to do with controlling the overdrive function.
Usually though, a fault with the overdrive could be related to the coolant temp sensor located near the thermostat housing on the gas powered engines. Most times though, if the ECT sensor is faulty, then the torque convertor lockup will also be disabled.
Count how many times the engine shifts getting above 40 MPH, then, touch the brake pedal, not step on it, just a touch, the engine should gain a couple hundred RPMs when the brake pedal is touched. If You count four shifts, then the OD is probably functioning and the TCC lockup is failed.
Welcome to the forum. Those with more knowledge will most likely come in and post a bunch of stuff I either forgot, or, dont know about.
Unless they is all out camping, fishing, wood cutting or just in he eral goofing off.

Thanks I've had issues both speed sensor pigtails were bare wires replaced those and speed sensors. replaced ignition switch per low voltage helped for a minute. od works for along time unless I get over 55mph. 99% sure something electrical is the issue

 

[ak diesel driver]

Sure that's not code 86?

 

[THEFERMANATOR]

Code 68 for an obd1 4l80e is for trans component slipping. You need to get a scanner on it and monitor input vs output speed sensor readings to get calculated gear ratios and to find how much slippage you're getting. Code 68 is pretty common when your direct clutches are gone.

 

[Haasbuilt]

Code 68 for an obd1 4l80e is for trans component slipping. You need to get a scanner on it and monitor input vs output speed sensor readings to get calculated gear ratios and to find how much slippage you're getting. Code 68 is pretty common when your direct clutches are gone.

I have no slipping just hoes into lock up

 

[THEFERMANATOR]

View attachment 62118

OBD 1 code 68 has nothing to do with the transmission. AC compressor relay fault. It could be the same circuit might have something to do with controlling the overdrive function.
Usually though, a fault with the overdrive could be related to the coolant temp sensor located near the thermostat housing on the gas powered engines. Most times though, if the ECT sensor is faulty, then the torque convertor lockup will also be disabled.
Count how many times the engine shifts getting above 40 MPH, then, touch the brake pedal, not step on it, just a touch, the engine should gain a couple hundred RPMs when the brake pedal is touched. If You count four shifts, then the OD is probably functioning and the TCC lockup is failed.
Welcome to the forum. Those with more knowledge will most likely come in and post a bunch of stuff I either forgot, or, dont know about.
Unless they is all out camping, fishing, wood cutting or just in he eral goofing off.

Code 68 for multi port fuel injected cars is for the ac, tbi trucks are different. This is part of the reason for obd2 and universal p codes. Oem hex codes could have multiple meanings depending on the platform it was in.

 

[THEFERMANATOR]

I have no slipping just hoes into lock up

Code 68 means it detects slippage. Just because you don't notice it does not mean it is not slipping. Since you say it does it in 4th, it may be your converter slipping which is not that uncommon for valve body wear in the tcc valve bore. They sell a tcc lockup valve that has a seal on it for this problem. You need a scanner on it so you can see what it is seeing.

 

[Haasbuilt]

I did notice that if I'm driving in town or under 55 seems to give me all 4 gears. Over 55 locks back to 3rd until restart

 

[WarWagon]

Your ECM is stopping the "slipping" before you notice it. Higher speed mean more load till the weak link slips and you get Limp Mode. In the old days the trans would simply slip till it burnt clean up and you walked. Anytime I have seen this code it was time for a rebuild. One time it was because the OD section went "BOOM!" and they couldn't say what failed first the sprag or a bearing, but, the debris went through the OD gearset. Another time is was me overpowering a weak TC clutch.

At this point you need a scanner or a trans shop: the only question is can you get away with a repair as outlined above or does it need a rebuild.

 

[THEFERMANATOR]

There is nothing more you can do without a scanner to see what it is seeing.

 

[Dumptruck454]

4080e it's in a '93 dump truck two-wheel drive shifts into first the second and then shifts back in the first unless you let off the gas does the same thing and second and third and then kicks out of overdrive going down the road and will not kick back in unless you shut it completely off and the speedometer is off it shows 45 and I am really running 60