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Discussion Starter · #1 ·
I've been dealing with a "gearbox fault" message for a while now. The "D" on my dash will flicker followed by the fault. Then she locks into, I think, 3rd gear. Sometimes it does it, some times it's ok. I had the fluid checked and it was low. The truck has 133k miles. I had my indie put in a new pan/filter kit and add the appropriate fluid. I don't know if it was ever serviced before me. The fluid looked pretty crappy with a good amount of metal 'sludge' at the magnets. Obviously with the new fluid, There's still some fouled fluid mixed in as you can't drain all of it out of the torque converter. It seems to be getting the fault less often now that some new fluid got cycled in and is definitely better once it warms up. This leads me to believe it may be a fluid issue.
Here are the codes I get:
U0402 Invalid data received from transmission control module
P0850 park/neutral switch input circuit
P0915 Gearshift position - circuit range /performance.
Sometimes I get the added, "HDC not available" as well. Usually the parking brake will be engaged on its own without me setting it too.
As these are shift by wire controls, there's no physical switch mounted at the transmission with a cable to check.
Can anyone explain how the shifter and transmission communicate?
When the issues is not present, she runs great, smooth shifting with no issues at all. So I don't think it's something inside the transmission unless it's one of the solenoids getting it's communications corrupted.
I've changed the battery twice just to make sure that wasn't the cause. The alternator I'm told is fine.

Any thought/ideas would be appreciated.
 

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The lights on the dash are driven by the switches on the actual shifter handle in the console. The display of 1,2,3,4 etc in the digital part of the dash are driven from the TCM when the shifter is in sport or manual mode based on info from the TCM. The shifter handle just puts the transmission into park neutral drive and reverse via a cable. The rest is done by the TCM. If the shifter cable gets out of adjustment you start to get the weird transmission fault messages, and it doesn't take much. Try to readjust your shifter cable down at the transmission end. It's pretty easy.
 

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Discussion Starter · #3 ·
I don’t believe these have a cable. I’m told they are shift by wire. No cable. All electronic
 

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Dave,

If you take the time to remove the center console, lo and behold you will discover a cable connected to the left side of the shifter assembly :)

From your description you may have either an electronic connectivity issue or, if you believe that the fluid and filter change improved the transmission's performance, a still partially contaminated fluid content.

If you slide your transmission lever to the left, do you have full "manual transmission" up and down shift capability?

The transmission module is mounted under the hood directly in front of the brake pedal area. It is mounted on the back side of the left front strut tower, in an inverted fashion with the module connectors connecting from the bottom.

Occasionally, rodents chew on various electronics under vehicle hoods, causing all sorts of problems to electronically controlled systems. The module's plugs are color coded so it's easy to return them to their correct slots. You may want to slide the module up from its perch and take a look at the wiring to ensure it's not been previously chewed on. You'll need a 10mm socket to remove the fittings around the module to gain access.

The transmission lever's electric sensors are connected to the transmission module thru connector plugs at the foot of the driver side A-post, behind the large plastic trim which also has the left foot rest attached. You can remove this trim by pulling off the foot rest pad and undoing the 10mm nut which hold the trim in place.

Once the trim's removed check for any corrosion on the large black and white connector plugs' pins.

Rob
 

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Discussion Starter · #5 ·
Thank you, Rob. I swapped out shifter with a used one and got the same result. I’m going to follow the trail you just laid out before I cycle in more clean fluid.
 

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Discussion Starter · #6 ·
Still chasing this problem. I swapped my shifter and swapped in some more clean fluid, but she's still throwing the gearbox fault periodically. Seems to be less prevalent after she's been running for a while leading me to think either fluid (consistency changing after warm up) or if it's a charging issue. Some days I get in and there's no "P" illuminated,so it won't start until I try multiple times and keep resetting the codes. I've had multiple people tell me the battery (new, AGM) and alternator are good. My suspicion is that it's the alternator. Yes, I've followed the sticky on that one. What exactly does that cable from the shifter connect to? If it's an electronic system (shift by wire), I don't follow what it connects to.
 

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Dave, Mark is dead on and you have now compounded the issue by changing the shifter with a used one. Please help yourself out of this situation and download the 2010-2012 shop manual. The link is in the ** START HERE** FAQ stickie at the top of this forum section. Then you will have photos and step by step directions to adjust the cable.
 

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Discussion Starter · #9 ·
I really don't think its the cable. I just tried changing the shifter in case maybe I spilled something on it, which I'm sure I didn't. Although my HDC button was real sticky. I removed it and cleaned it, but it hasn't been available since. Do you think that could that be a root cause of all of this? It flickers the gear on the dash, (P,N,D) when engaged. That's when the gearbox fault appears. Sometimes it just vanishes for a while and then pops back on. I reset it and it works perfectly. Shifts as smooth as can be. Until it happens again. What are your thoughts on the fluid causing this or maybe a bad solenoid at the magnatronic? The fluid was pretty dirty. Could metal shavings in there be grounding something out inside the magnatronic? That's why in my original post I asked how the transmission communicates. Thank you for your ideas. I'll still take a look at the cable regardless. As soon as I have some time.
 

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I'm looking at the P0850 and P0915 codes you have which screams shifter cable adjustment, or faulty PND position switch. The PND switch is inside the transmission, and is part of the mechatonics unit so you will hope it isn't that (see post 7 in the link above its the orange colored thing in the drawing). Adjust the cable, it takes 10 minutes and is far easier than draining fluid, if it doesn't work you're out nothing but 10 minutes of your life. When the light flickers on the dash, the TCM sees that as the transmission is going from D to N, or P to R, but the gears are still spinning so it produces the fault to prevent or minimize damage to the transmission. P,N, and D indication on the dash is solely driven by that cable, if that indication is wonky its because the shifter cable is out of adjustment or the operating linkage on the transmission is rusty and sticking (ie not rotating far enough to get to the commanded position). If you see a pile of rust on the linkage bolt be extremely careful when the nut is loosened that the stud does not break off, because if that happens you will need a whole new actuator rod, which extends across the entire width of the transmission and it requires the transmission to be removed to get clearance to pull it out. If you can find the part.

If the electronics of the mechatronics were faulty you would get a code for that. They could be out of spec and not have a code, but since the issue seems to correspond with the lights on the dash I would start with the simplest change first, then worry about digging deeper.
 

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I really don't think its the cable. I just tried changing the shifter in case maybe I spilled something on it
so why didn't you just clean the shifter instead of replacing it? Until you properly adjust the cable you are just chasing your tail and tossing money around the root issue.

if you have metal shavings in your transmission you have far bigger issues to deal with. You just had a new pan and filter installed. Wouldn't your indie have mentioned any shavings?
 

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Discussion Starter · #13 ·
so why didn't you just clean the shifter instead of replacing it? Until you properly adjust the cable you are just chasing your tail and tossing money around the root issue.

if you have metal shavings in your transmission you have far bigger issues to deal with. You just had a new pan and filter installed. Wouldn't your indie have mentioned any shavings?
I left out the part about cleaning the original shifter. That was what he did first which is why I tried another shifter. As for the metal in the oil, it was more of a good build up at the magnets. The transmission has 130k miles and I only have service records up to 80k. I bought it with 120k. So I'm assuming it's the original fluid and that some metal 'silt' at the magnets was acceptable with it's mileage. I'll be checking the cable this weekend. I attached a short clip of what the dash looks like as the indicator blinks on and off.

 

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Discussion Starter · #14 ·
So my indie says it’s definitely the valve body. I brought it to the dealer to confirm. Of course they say a new transmission is needed, but I was able to spend some time on the phone with the technician. He agreed that it’s the valve body. I was hoping it was just the bridge seal or something similar. Just updating in case someone else gets this issue and needs opinions.
 

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Why not at least attempt to replace the bridge seal?

I would..

A drop mechatronic unit, replace bridge seal and tube seals
B add a transmission additive for anti shudder
C assemble and clear transmission adaptations and drive it softly for the next 500-1000 miles



Sent from my iPhone using Tapatalk Pro
 

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Discussion Starter · #16 ·
I was thinking of doing that. What additive would you recommend? I know these are very fluid specific so I don’t want to exacerbate things with the wrong additive. Thank you for your input.
 

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Discussion Starter · #17 ·
The only reservation I have is that from what I’ve read, if it’s the bridge seal, the problems arise after the fluid warms up. My situation is the opposite. It gets better (goes into Fault less often) after it warms up.
 

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I've been dealing with a "gearbox fault" message for a while now. The "D" on my dash will flicker followed by the fault. Then she locks into, I think, 3rd gear. Sometimes it does it, some times it's ok. I had the fluid checked and it was low. The truck has 133k miles. I had my indie put in a new pan/filter kit and add the appropriate fluid. I don't know if it was ever serviced before me. The fluid looked pretty crappy with a good amount of metal 'sludge' at the magnets. Obviously with the new fluid, There's still some fouled fluid mixed in as you can't drain all of it out of the torque converter. It seems to be getting the fault less often now that some new fluid got cycled in and is definitely better once it warms up. This leads me to believe it may be a fluid issue.
Here are the codes I get:
U0402 Invalid data received from transmission control module
P0850 park/neutral switch input circuit
P0915 Gearshift position - circuit range /performance.
Sometimes I get the added, "HDC not available" as well. Usually the parking brake will be engaged on its own without me setting it too.
As these are shift by wire controls, there's no physical switch mounted at the transmission with a cable to check.
Can anyone explain how the shifter and transmission communicate?
When the issues is not present, she runs great, smooth shifting with no issues at all. So I don't think it's something inside the transmission unless it's one of the solenoids getting it's communications corrupted.
I've changed the battery twice just to make sure that wasn't the cause. The alternator I'm told is fine.

Any thought/ideas would be appreciated.
Older topic but correct info may help the future. The 2 codes are relationship based in most cases. You have the gear position switch aka PRNDL aka P/N switch, and the shifter position switch. They both are monitored for both codes, but it gets a little funny because depending on the conditions, and type of issue, either failure can set either or both codes. When it sees you depress the brake pedal and press start/turn key, it EXPECTS that the 2 switches indicate trans actually in PARK/N and shifter in Neutral. If they are in a different position than each other, youd more likely get an 850 code..especially if its a coffee based fault in the gear shifter. HOWEVER, the car has no way of knowing WHO is lying/mistaken. The gear position switch is inside your mechatronic unit (Its inside the tranny) so you hopefully dont have that as your issue. Your main ground for the Mechatronic (On yours, it varies a little from model to model) is on the left side shock tower top. (There are other grounds on front or side, ignore those for now). You can try checking that but it will likely not be your fault if the probem is intermittant and even moreso...if ground IS your fault, testing there wont provide useful data. Ground/Earth means zero volts AFTER current flow has carried voltage to ground/ battery negative zero. The issue with testing is you must test on the UPSTREAM side of a fault.

Example/ lightbulb takes 2 wires, a power and a ground. power side is good. Ground is bad right at the battery where it connects back to source. If you test at the bad negative battery connection you may see a number that isnt near zero like it should be. It may be 2 or 5 or 11v, it may be 500mv, doesnt matter. It means your ground is bad because where you are testing there is voltage that moves at the speed of light (all electricity does) and it was there hanging around rather than returning to the battery and showing ZERO. The force preventing it from returning to ground is called RESISTANCE. Problem comes in where you test. lets say your resistance ISNT at the battery cable connector, but at a plug that got wet 2 feet from the battery. If you test at THAT plug you may see 3v on the ground wire showing reistance and voltage that couldnt make it back home because the resistance blocked it. BUT, if you tested at the battery youd see ZERO, because the trapped voltage isnt where you are testing. If you test at the light bulb right up to the bad connection, it will show the resistance at ANY point...same number. If you go past the bad spot, you dont have excess current that cant reach ground anymore. Thats all trapped ahead of where you are testing, what little is getting through that bad spot will happily run straight to ground from the bas spot to the battery.

The point on the shocktower is where the Mech unit attaches to earth/ground. The end of the line. You need to test at the transmission plug (right side bottom of trans, round plug, 14 wires, you want BROWN wire). If you test THERE and see voltage above 100mv WHEN the dash cluster flickers, the problem is your ground SOMEWHERE between the trans and battery negative, if you DONT see voltage show up when the problem is occurring then your problem is elsewhere. Voltage drops are very useful for eliminating or proving what is really at fault rather than guesstimating from symptoms. Throwing an ignition coil that costs 60 bucks at a misfire is a guess that wont hurt that much if you are wrong. a shifter is hundreds...a complete mech unit is THOUSANDS! Do the testing!

Its sounding from description like your mech wiring or unit may be the next stuff to test. The position slider for the shifter is very easy to change. They dont/didnt used to sell it seperately, but if you can find a used shifter you can change it out in 30 or 40 minutes with a t20 TORX and a pocket flat blade screwdriver. Pop console center up which is 8 torx screws total, 2 under side trim, 2 under door, lift box when the door ones are out, uyoull see 2 more, pop small insert at front of center plate out with flat blade...2 more under it, remove 2 torx bolts, remove slider, drop new slider in, reassemble.
HOWEVER, that is the code tester and crank enabler and consile indicator lamp more than anything else. the actual cluster gear display comes from the PND switch which is inside the mech unit. Yours flickers when it screws off...so more likely thats where your problem is coming from. If its not powers or grounds to the mech unit (Test at the module or at the round plug), your problem may be internal which will be expensive.
 

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The only reservation I have is that from what I’ve read, if it’s the bridge seal, the problems arise after the fluid warms up. My situation is the opposite. It gets better (goes into Fault less often) after it warms up.
Dave: do you have time to update on this issue? I have the same problem right now and would appreciate your input.

Thank you
 
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