dave moonehy

I have a 1996 K2500, 94,000 miles.
.
Just bought it. Drove it 2,500 miles no issues.
Then this "limp mode issue."

I took it to a independent tech. Pd. $70 to pull codes as he has the $5K Snap on tool.
These are the codes:

1122 TPS int.low voltage
0756 Shift Sol.B stick off or 2/3 valve body performance
1870 Trans.comp. slipping
1871 Undefined gear ratio

I replaced ISS and OSS with new AC Delco parts.

Problem still happens intermittently; I can pull off the road and turn key off, wait a few seconds and turn truck on and drive off with normal transmission operation.

I just ordered new shift solenoids A and B and will drop the pan, and change those out.

Next on the list is to check the ground from ECM to truck firewall and clean all contacts with spray cleaner and reconnect.

After that is to replace the ignition switch.

I don't want to throw parts at it but it's the track I'm going down.

Can anybody here help me troubleshoot this problem? Thanks in advance.

Allan In NE

Hi Dave,

I don't like that undefined ratio code. That "usually" means that the transmission is slipping.

Pull the dipstick. Is that oil dark brown to black? If so, she's flat gotta come out of there for a rebuild. If it is pink yet, you're probably right in gambling on solenoids.

The way I would go about it tho, is to clear all the codes, drive until it goes into default, then immediately check the codes at that point. That way, you don't have any prior history clouding this new issue.

Allan

dave moonehy

Thanks Allen:

Just called tech. He's thinking it's the TPS circuit since this code keeps coming up, even after he cleared it.

Tranny fluid is clean and pink. History: at 84,000 tranny was flushed, conditioner pack, and new fluid, all 22 quarts or so new fluid.Also TPS was replaced and that code was cleared, all by the Napa Service Center.

Tech thinks that if the TPS sets a code, the tranny goes into limp.
He wants me to check for any shorts along that wire, including in the corregated plastic housing covering the actual TPS wiring circuit.

Thanks for reviewing this info as it may help. I'm hoping my tranny is not fried.
LOL.

dave moonehy

Update today:

Unplugged TPS, checked wires for fraying, shorts, etc.
Removed TPS, cleaned inside by blowing soft air on the internal pins inside the round female connector. Re-installed and reconnected.
Ordered a new AC Delco TPS, not a huge amount.Will have tech, clear codes and see what gives next.

Next I test drove the truck 8 miles, shifted flawlessly thru all 3 gears and 4th (OD)
and I took note of the rpms at shift points and in OD cruising at 60-65mph.
Truck drove as should.
Also checked tranny fluid. Looked pink and clear, not dirty brown and burnt smell.

I hope these notes may help anybody here help me solve this intermittent "limp" mode that has been a "plague" of sorts, this is my first GM product in some while, previously way fewer sensors and electronics to trouble-shoot.My friend said it's like being a "detective." LOL.

Allan In NE

This is good news. The pink oil, I mean. :>)

Yeah, he's right. If the TPS is bad, it will absolutely drive that tranny nuts.

The thing is, we've got to narrow this thing down. If the tps doesn't cure it, clear the codes again and keep at it working on the smallest codes first as they are "most often" the culprits.

Now, the next time you service that transmission, you've simply got to replace that filter. Using those "flush machines" just doesn't cut it..........Unless you're the lazy guy doing the work. They are nothing but an easy way to separate you from your money.

Keep us informed,

Allan

dave moonehy

Thanks Allan:

I can tell from your posts I'm headed in the right direction.
I 'll install the new TPS even though the one that is on there is only 10,000 miles old, it's one step closer to troubleshooting the P1122 code.
That code has been with the truck since the 84,000 mark as far as I can tell when the tech that did the work installed a brand new TPS and "cleared the code P1122' at least that is what the receipt says.

I can appreciate a bad TPS circuit, wire or sensor absolutely driving that tranny the 4L80E nuts.

Appreciate your patience as I trouble shoot my way thru the "problem."

Dave

dave moonehy

Allan or others:

This question is regarding "smallest codes first" as "most likely culprits" in my trouble shooting to narrow down this problem.

P0756 is my lowest numbered culprit.

It looks fairly easy to drop the pan and change out the solenoids A and B being careful to not lose any of the springs, valves, etc.

8 qts.of new tranny fluid, new gasket new filter.
One question, when I remove the crossmember will a jack under the transfer case keep the tranny supported as it looks like to properly torque the pan bolts. Also rubber or cork replacement pan gaskets, any preferences?
Also is any rtv or other sealant applied on re-install.I haven't wrenched on an auto tranny, this will be my first attempt.LOL.

Thanks in advance for any and all input, Dave

Allan In NE

No need to remove the crossmember at all.

Roll a jack under the transfer case, rattle off the two nuts on the adaptor mount and jack 'er up 'til the whole she-bang hits the floorboard.

Rubber gasket and ABSOLUTELY NO RTV OR ANY OTHER SEALER!!!!!!!! Transmissions don't like that stuff!!

Allan

dave moonehy

Thanks Allen:

I can tell you've wrenched on these GM trucks, appreciate it.
After my new TPS and solenoids A and B come and parts are installed, I have the codes cleared and road test,looking for the smallest codes first.
Dave; working to narrow this done,as you said.

sholaway1

I know this is a very old thread but My truck had intermittent sometimes I could turn ignition on and off and it would work. Now it is steady. I have no gear selection indicator, no Speedo, no tach my trans has no 1st gear and no high gear only end and third and only second if I shift manually to first or second. Any ideas .... I have unplugged trans to see if it would manually shift thru gears but nothing. I have checked the plugs for corrosion on my neutral safety/shift position sensor on drivers side of trans. I have been told it's a corrupt ecm I'm not convinced.... Any test I can run say at steering column to see if ignition switch is even sending a signal to pcm? Hopefully I can get a quick reply e-mail would be awesome sholaway68@gmail.com

I have codes p1180 and 1184