Hard Shift 1-2, no 3rd. U0100

[Instrumental]

Just happened this morning. Had a bad snowy drive to work this morning, towing a trailer no less. Went to leave later in the morning and this.

I've got an engine light throwing the U0100 code, which is loss of communication with ECM/PCM. I can't find much about this as it relates to the Trailblazer platform.

The shift indicator is only lighting up in 1, whether I'm in Park, Reverse, Neurtral, Drive, anything. It has a nasty hard shift from 1st to second unless I'm super light on the throttle. It will not go to 3rd or even give me revs even when the throttle is floored. I made a very slow climb up a hill towing the trailer. My Torque scanner will show the error code, but won't give me any of the real time info like rpm, throttle, etc.

I gave it a quick once over looking for blow fuses or frayed or damaged wires, looked for corrosion on the connections, and nothing so far.

Any thoughts? This has thrown for me a loop, as I don't see a direction to go at the moment.

 

[Matt]

Check this thread out, there's a bit of trouble shooting info: http://www.tbssowners.com/forums/tb...s-rough-surging-acceleration-hard-shifts.html

Further in that thread, someone else was having the issue, they replaced the ignition switch and it was solved.

HTH

 

[Instrumental]

I did read that one, and if thats the case I might be in a world of hurt. I believe the Saab ignition switch is custom as its in the center, and my quick research so far is that its not available anywhere.

 

[Matt]

I just looked at O'Reillys and they have either the Dorman at the store or AC Delco as a special order. Amazon has them as well as Rockauto, if I'm looking at the right thing.

 

[Instrumental]

Reports are that it'sthe standard trailblazer version and won'tfit the Saab. I cant getnit in anywhere until Monday, so I may as well pull that this weekend and check it out.

Its weird to me that it was instant fail, most people report intermittent issues to start, and it has had zero affext on starting the engine.

 

[Mooseman]

The ignition switch is very different. It's a PassKey3 using a chip whereas all others are PassLock without chips. Used may be the only option if it needs to be replaced. On top of that, you'll need a Tech 2 to reprogram the BCM for this replacement as well as the security module to accept the chip sensor and new keys. The joys of owning an oddball truck.

You should troubleshoot at the switch to see if you are getting power as you should when the key is turned before just replacing it.

 

[Instrumental]

Got advice today from a GM mechanic that the park/neutral safety switch on the transmission may be the culprit. The indicator stuck in 1st was a clue, so I think I'll try a part swap on that first. I'm ok with laying out 40.00 for that to give it a shot.

This diagnosis make a lot more sense to me, the car starts and runs just fine and has never given me even a hiccup in that regard.

 

[gpking]

I had some similar issues this past summer with the transmission losing gears and some odd codes (like failed airbag sensor, failed transmission pressure valve position switch, service 4WD, lost PCM communication, etc).
After throwing some parts at it (ignition switch & transmission pressure valve position switch) and cleaning and re-seating the following connectors the gremlins have gone away for good. I'd definitely check these connectors before throwing parts at it.

 

[Instrumental]

The one on the right I did check, there was no sign of any corrosion or dirt there. The 3 on the left I think are located lower down on the 5.3. I did check one of the connectors, but they're not so convenient to get at as that. I'll take a second look and see if I can get at them.

 

[Reprise]

The 3 on the left are '2' on the 5.3, and they're between your battery & fan shroud (at least they are on my Envoy.) They are lower, as well.

Since those are your PCM connections, it might be a good idea to disco the battery before doing anything with those connections, just to be safe.

 

[Mooseman]

There's the PCM with 2 connectors there and the TCM (Transmission Control Module) with 1 connector directly behind it. They are separate on the V8.

 

[Reprise]

Ah - I didn't realize the '05-forward TCM termination on the engine side was in the same area (raising the total to '3').
Curious - same 80-pin connector as the two for the PCM ? I'll need to look this up online for a view.

 

[Instrumental]

Just got my baby back today, was in the shop for a week and a half. They wete busy and didnt put any real time into it until this week.

Turns out it was one corroded wire somewhere in the loom for the tcm/ecm. He showed it to me, it was a tiny nick in the insulation and the wire evetually ended up as green powder. It was in a loom, and pretty sure under the hood. Best guess is that it might have happened as far back as the factory and just took this long to rot out.

Had them do a pan drop amd filter while they had it, so its got a clean bill of health now. At least until the next bit of fun pops up.

 

[Mooseman]

Yep. Seen that before on something else. It happens.

 

[Instrumental]