Transmission code 74 help needed

[steelsoldiers]

Hey guys,

Sorry I haven’t updated my M1152A1 build thread in a while. Got busy with some family activities this summer and slacked off. I will update it soon!

That said, I have been driving my HMMWV to work and around town some. The transmission seemed to be working pretty well after I worked some initial bugs out of it including replacing the TCM and repairing a bad wire to the check light. Recently, it has stopped going into OD and is a little slow going into Reverse (maybe takes a second or so). The shifts between 1-2 and 2-3 are nice and smooth, no slipping and fluid is normal in level/color/smell. Jumping the terminals on the test plug revealed a code 74, so I started following the troubleshooting section in the trans manual. The resistance on the TISS was in range, but I put a new one in just in case. Also, the wiring showed continuity between the TISS and the TCM. The only other issue I have found is some ATF in the connector at the transmission, so it looks like its seal is failing. The TCM is new. The wiring in the battery box all checks out. Grounds are good.

Anything else I should check? Could fluid contamination in the connector be causing all of the issues?

I hate to take it to a transmission shop, but I am not sure what else to try at this moment.

 

[NDT]

Have you followed the troubleshooting tree on page 103 of Supplement 7? Code 74 is why you have no lockup.

 

[TOBASH]

hope this helps.

 

[steelsoldiers]

As I mentioned in my post, I already followed the troubleshooting guide for code 74 by checking resistance across the TISS and checking for continuity of the TISS wires. I don’t have a Tech 2, so haven’t tried jacking the truck up and increasing the speed to 10mph.

 

[TOBASH]

Did you open plug and ensure all pins are free from corrosion and crap?

Have you opened new TCU and done the same as they get water and corrosion inside too?

 

[steelsoldiers]

Canon plug looks good. Only corrosion was on the test socket on the TCM box because soldier B left the cap off. The inside of the TCM is clean and dry.

 

[TOBASH]

Canon plug looks good. Only corrosion was on the test socket on the TCM box because soldier B left the cap off. The inside of the TCM is clean and dry.

Just for the heck of it, open box and unplug and replug everything.

IMHO

 

[steelsoldiers]

Just for the heck of it, open box and unplug and replug everything.

IMHO

Tried that a couple of days ago. No change unfortunately

 

[steelsoldiers]

Was just reading in the TM and it described how the fan cutoff switch and the TP sensor are used to tell the transmission when to kick down. My fan has been acting a little erratically and when I looked at the fan time delay module the other day, it looked like there was some green silicone like goop dripping out of it. I don’t remember seeing that when I was prepping that area for paint. Wonder if the TDM has overheated? Also, wondering if the fan cutoff switch or the TDM could be confusing the TCM and preventing OD or if they’re two separate issues? I checked the TP sensor and the voltage is in spec there.

 

[Mogman]

If you are getting a 74 code then you still have an issue with the TISS
If all the voltage and ohms check out all the way to the TCM (pins D4/D3) then the TCM is possibly defective as it is a relatively simple circuit.
If the voltages do not check out then it is possible the new TISS is defective.
Curious have you taken contact cleaner and cleaned the trans. connector and harness plug where there is oil present?

 

[steelsoldiers]

If you are getting a 74 code then you still have an issue with the TISS
If all the voltage and ohms check out all the way to the TCM (pins D4/D3) then the TCM is possibly defective as it is a relatively simple circuit.
If the voltages do not check out then it is possible the new TISS is defective.
Curious have you taken contact cleaner and cleaned the trans. connector and harness plug where there is oil present?

Okay thanks. Just wanted to make sure I wasn’t missing something else. I will pull the cover off of the TCM box and see if the resistance matches what I’m seeing at the TISS. I think it was around 1350 and it’s supposed to be between 1000-2000.

I did clean the trans connector thoroughly with contact cleaner, but there was some more ATF residue on it when I checked it again the other evening, so it definitely looks like the seal is seeping.

 

[steelsoldiers]

If you are getting a 74 code then you still have an issue with the TISS
If all the voltage and ohms check out all the way to the TCM (pins D4/D3) then the TCM is possibly defective as it is a relatively simple circuit.
If the voltages do not check out then it is possible the new TISS is defective.
Curious have you taken contact cleaner and cleaned the trans. connector and harness plug where there is oil present?

I checked continuity and resistance at the D3/D4 and it’s definitely in spec. Hate the thought of buying another TCM, but I can’t think of any other possibilities.

 

[Mogman]

PM sent

 

[TOBASH]

Feel your pain brother.

 

[steelsoldiers]

I hate when people post these threads asking for help and then don’t share about the resolution of the issue. I realized this morning that I was one of those people. Sorry

I ended up borrowing a TCM from Mogman. It allowed my truck to run through all 4 gears, but the shift points were a little high/firm for my liking. At least it showed that my trans wasn’t completely FUBAR. After that, I bought a good takeout TCM box and TCM on eBay. I was a little concerned that my TCM box connectors could be corroded and could be contributing to the erratic behavior. The “new” box and TCM worked great and did not cause any error codes to set. The shift points were still a little high/firm for my liking, but I was able to adjust the TPS and now they feel good to me.

The truck has been sidelined with a split half shaft boot for the last couple of weeks, so I haven’t put a lot of miles on it yet. I got the boot fixed yesterday, so I plan to drive it more this coming week and then take it to a local truck shop to have a fluid/filter change and a new harness connector installed.