6.0 Engine and Transmission Emergenct

[AlexMahon]

2008 Yukon 1500 XL SLT with 6.0L & 4L70-E trans; approximately 155K miles; everything re: engine and trans working great. Parked vehicle for about 45 minutes. Came out, started up, check engine warning symbol. All instruments OK except oil pressure - not registering any oil pressure. No smoke; no odors; no signs of leaks on ground; all re: engine seemed good. Drove out of parking lot - the trans was upshifting quite/abnormally hard. Engine temp stable at 210 degrees. Once shifted into OD at 45 MPH all seemed normal except oil pressure gauge. Drove 2 miles to mechanic shop and dropped off for analysis. Any ideas out there?

 

[strutaeng]

Maybe wiring and/or sensor issue.

Sounds like it has oil pressure if you drove it to the shop. At least enough pressure to not knock or throw a rod or seize.

Wait until they diagnose it properly.

 

[Ibustbravo]

Without any logging, we're just guessing.

You sure you didn't accidently hop into someone's Ford truck? ;-) They tend to act out like this.

 

[tooleyondeck]

Sounds like a bad oil pressure sensor, but that wouldn’t affect shifting, so there are two separate issues here. Possibly a ground issue with the TCM?

I’m interested to see what the tech says. Best of luck!

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[dkad260]

Welcome!

Did you by chance pull the dipstick to verify oil level?

I had this happen to my 2012 Yukon, gauge went to 0 then later pegged, was a faulty oil pressure sensor.

Keep us posted.

 

[AlexMahon]

Welcome!

Did you by chance pull the dipstick to verify oil level?

I had this happen to my 2012 Yukon, gauge went to 0 then later pegged, was a faulty oil pressure sensor.

Keep us posted.

Problems resolved. It was apparently a coincidence that the transmission (hard shifting) and zero oil pressure problems occurred simultaneously. Or the electrons revolted and enlisted the PCM to highjack the TCM.

The oil problem was the harness/pigtail, not the oil pressure sensor/switch. The technician spliced in a new pigtail/connector and the oil pressure now reads 30-40 PSI at 1,500 RPM.

I reset the TCM via the internet/Google/YouTube instructions and now all is well.

Thanks for your input.

 

[Geotrash]

Problems resolved. It was apparently a coincidence that the transmission (hard shifting) and zero oil pressure problems occurred simultaneously. Or the electrons revolted and enlisted the PCM to highjack the TCM.

The oil problem was the harness/pigtail, not the oil pressure sensor/switch. The technician spliced in a new pigtail/connector and the oil pressure now reads 30-40 PSI at 1,500 RPM.

I reset the TCM via the internet/Google/YouTube instructions and now all is well.

Thanks for your input.

Awesome! Thanks for following up. There is no substitute for a tech who is willing to take the time to troubleshoot properly before throwing parts at it.

 

[Just Fishing]

Common for the pressure switches to go south.
I have to wonder if the bad wiring maybe shorted and caused the ecm to go "Wtf" and go into a "Safe mode" of sorts.
I understand that if things go bad the transmission will go to a default mode and start shifting hard?
Maybe I'm making that up.

These things can have a bunch of codes to go along with a simple engine code.

I remember taking my intake off for the first time, I decided to clean the throttle body while it was apart.
When reassembling I needed to go through a learn procedure.
the result was a code and a bunch of other non-related lights regarding the traction control and stability control?!

I also love how my transfer case can throw a code, and then lock me into 4x4.
either clear the code or pull the negative term off of the battery to reset.

I had that happen while in Auto 4x4 a few weeks ago, I didn't have my code reader with me, so I was forced to do a manual reset via battery.

Reminds me, I need to toss my scan tool back in the tahoe for some planned weekend adventures coming up.
Just in case!

I would hate to be hours away from home and stuck in 4 low.
Or be forced to drive home in 4 high.

Silly complex vehicles.

 

[AlexMahon]

And now, the end of the story. Remember the oil pressure sensor pigtail wire that was frayed and fixed by the independent shop tech without having to R&R the oil pressure sensor switch? The hard shifting that required the TCM to go into the relearn mode? Those two issues were quickly followed by a very poorly running engine that two independent shop techs could not figure out. Codes that were traced to Cylinder 6: P017 (System Too Lean Bank 2); P1175 (Fuel Trim Cylinder Balance Bank 2); P3441 (Cylinder 6 Deactivation Solenoid Control Circuit). All cylinders were compression tested to 153 +/- 3. No loose wires. No apparent vacuum leaks. The intake manifold gasket was checked good. Etc. Nothing. I finally took it to a GMC dealer. The tech there figured it all out upon removing the intake manifold. Apparently while I was in the doctor's office (for about 45 minutes), a rat or mouse had raided the engine compartment and nibbled on the oil pressure sensor wire, the 12V power wire, and the cylinder 6 solenoid wires going to the valve lifter oil manifold. The tech soldered two new sections of the wire and verified repair. Engine now runs good, as normal. I don't know what the lesson is here, but tuition was about $918.