[driven2exceSS]

Anybody know anything about this code (P1839) and how to make it happy again? I'd like to enjoy my second HPDE day (tomorrow) at the Glen without having to go into limp mode I have an OBD reader and the code keeps coming back upon reset after a couple laps. I tried no tap, one tap, two taps, and long hold and it doesn't make a difference. Research is showing something with transmission?? Maybe I try running full auto and not manually shift it, but that scares me a little on unpredictability of shifts. I am calling the hometown dealer in morning for an appt as it will be less than a week till I have another two-day event back here!! Thanks in advance for any advice...

[DenverTaco07]

Is your transmission seem to shift ok? Maybe check in full Auto and in paddle shift modes.

That code might be related to a stuck transmission solenoid.

[driven2exceSS]

Yeah it actually has been shifting okay, and then also okay up to 4000rpm once it throws the code (again). I've continued to run in limp mode and short shifting before 4000 without problems too. Maybe I try the stick lever for shifting verses the paddles and see if that does anything. But overall nothing noted in the shifts prior or after code thrown.

[DenverTaco07]

Here are related DTC codes to P1839:

P182F, P18B7,
P18BC, or P18C1

P1839 according to service manual:

DIAGNOSTIC INFORMATION AND PROCEDURES > DTC P182F, P1839, P18B7,
P18BC, OR P18C1: INTERNAL MODE SWITCH C CIRCUIT > CIRCUIT/SYSTEM
DESCRIPTION
The internal mode switch indicates to the transmission control module (TCM) which gear position the
vehicle operator has selected. The internal consists of 5 separate hall effect switches. Each hall effect
switch is supplied a 9 V reference circuit and a signal circuit from the TCM. Each signal circuit for each
gear selector position will have either a voltage reading of 0.70-0.96 V indicting On or 1.68-2.38 V
indicating Off. The voltage values on each internal mode switch circuit will change and are dependent on
the position of the gear selector. The state of each internal mode switch A/B/C/P/S signal circuit is
displayed on the scan tool.

DTC P1839 activates on any of the following:

Internal Mode Switch C Circuit Low Voltage

TCM has detected the internal mode switch C signal circuit voltage is less than 0.7 V, for 1.75 s.

looks like some possible repairs related per service manual:

DIAGNOSTIC INFORMATION AND PROCEDURES > DTC P182F, P1839, P18B7,
P18BC, OR P18C1: INTERNAL MODE SWITCH C CIRCUIT > REPAIR INSTRUCTIONS
Perform the Diagnostic Repair Verification after completing the repair.
Automatic Transmission Fluid, Fluid Pan and/or Filter Replacement
Automatic Transmission Wiring Harness Replacement (Electrical Connector Passage Sleeve)
Manual Shift Shaft Position Switch Replacement
Transmission Control Wiring Harness Replacement
Perform the Transmission Service Fast Learn Procedure following all transmission related repairs.
Refer to K71 Transmission Control Module: Programming and Setup

[driven2exceSS]

Originally Posted by DenverTaco07

Here are related DTC codes to P1839:

Thank you Sir!! Great info... clearly something over my head!! But info to bring forth for sure! And ultimately to have as a reference through the process as the local mechanics back home go at it. Seriously I thank you for your time AND efforts!! MUCH appreciated

[DenverTaco07]

my pleasure, good luck, hope its something easy.

[ctrlz]

This sounds like an electrical connection problem with either the wiring to the transmission mode switches or the switches themselves. Based on the description above, it sounds like you might need to drop the pan to get to some of this.
Anything happen recently like detailing the engine bay or driving through deep water?

[driven2exceSS]

Originally Posted by ctrlz

Anything happen recently like detailing the engine bay or driving through deep water?

Negative and negative. Back in Feb/March it got a fluid change and was overfilled that sprayed the underneath a bit, plus the multi cans of brake fluid used by the second dealers mechanic fixing the first dealers overfill. But has run fine since, till present problem began. Thanks

[driven2exceSS]

Well my "hometown" dealer could not schedule me in till middle of next week, so car sits at another dealer that I found with availability, now car is waiting for part(s) to be overnighted. Looks like it will be out of pocket too... Guess that is no real surprise with my mods. Cha-ching cha-ching :( Positive forward outlook is that the car hopefully gets fixed appropriately, and this coming Mon/Tues at the Glen is more fun than this past Mon/Tues!!!

[TheRealJA105]

Your "limp mode" must be different than mine. When mine goes into "Reduced Engine Power" it literally will barely make it up out of the boot. It would take 2 minutes to wind out to 4k rpm. Also mine never throws a code, just the Reduced Engine Power on the screen.

[driven2exceSS]

Originally Posted by TheRealJA105

Your "limp mode" must be different than mine. When mine goes into "Reduced Engine Power" it literally will barely make it up out of the boot. It would take 2 minutes to wind out to 4k rpm. Also mine never throws a code, just the Reduced Engine Power on the screen.

Yeah it otherwise drove "fine" up to 4,000rpm then hit the rev limiter. I say "fine" because I believe I noticed a lil change in performance and sound, but didn't totally fall on its face till hitting the rev limiter. So whatever the technical term is. I've seen the "Reduced Engine Power" in action too, but not with this issue...

[TheRealJA105]

My car is at my dealer right now for 2 electrical bulletins I found that hopefully may be causing my issue. As my tach starts going crazy when getting hot before my reduced engine power.
PIC6299A: Intermittent Tachometer Fluctuation While Driving
#17457: Service Update - Instrument Panel Gauges Flutter, Multiple DTCs Set

[driven2exceSS]

Oh that does sound like a different issue no doubt. I certainly hope the dealers pull through on both yours and my fixes!!

[driven2exceSS]

Well it cost a pretty penny out of pocket, but they replaced the Manual Shift Shaft Position Switch. I also had them change the filter and also made sure they added the "New" Mobil1 transmission oil for good measure. The test will come on Mon/Tues.... 16,900miles