2011 LR4 with 211,000 miles
About one week ago my wife called to tell me that that transmission fault light was on. I came and got the car and drove it straight to get scanned. Initial faults were p0915 Gear shift position circuit range / performance and some p0402- Invalid data received to TCM . A P0850-8F Park/Neutral switch input circuit also was found. In the previous weeks leading up to this, there were intermittent charging faults, and a few parking brake faults. Before going on from here, let me add that a drink might have spilled and got the shifter area and the parking brake lever wet.

I drive the car some more and soon find it won't turn off because the dash says car not in neutral. Turn it off and all clears. Drive some more and transmission faulty shows. Put it in park and it won't shift out of park. Turn off again and all clears. This goes on for a day or two. Then car won't shift out of third. It wants to start in third and stay in third at all speeds. Finally, red and amber brake lights flash and here a beeping noise at every stop. Shifts normally and smoothly thru all gears but really glitchy fault.

Mechanic suggest I clean all the connectors under the shifter with electronic spray and dielectric grease. I do that and everything magical vanishes and car seems normal for a week.

Then today my wife calls and says there is a charging fault warning. I bring it home and get 14.5v while running and 12.5 when resting. Look underneath and see oil on alternator so likely valve cover leak. Original alternator also. Several hours later and transmission fault shows up again and it doesn't want to turn off or won't shift out of park. Even when tranny fault clears, all the sudden the orange parking light will come one, then the red and a parking brake fault.

I have felt an unusual clunk right before the rpms show the shift from first to second. Feels like hitting a small rut on the road or a freeway expansion joint, but road is smooth. Sometimes I think I hear a whine right after the small clunk. Cant figure out if a transfer case would do that or a spline is slipping in the front dif.

I've never serviced the tranny so fluid could be original to when we purchased it with 100k miles. I've changed both front and back diff fluids. I'll try to change the transfers case fluid but suspect this is not the issue. CV joints feel solid. Front Diff bushing looks good too.

Does this seem to be a charging / alternator / battery type glitch?
Can a transmission control module get glitchy if the fluid is really old?

I have another LR4 so I could swap the shift assembly or the parking brake switch to help test. I'm just at a loss of what to do next. Im praying it ain't the tranny and hoping its some electrical glitch.
Any advice welcomed!

 

It sounds like a CANBUS issue where one or more modules are not receiving the input they are expecting. Low voltage causes all kinds of communications issues in these vehicles. Test your battery at a parts store. Then using a scantool, try logging the voltage output on a test drive.

Once you've ruled out a voltage issue, I'd start by troubleshooting the shifter issue first, before chasing all the other issues at once.

If you have a known good shifter but not an oscilloscope, your best bet is to try to swap in the shifter and see if it changes anything. If there is no change, I would move on to the parking brake.