So I was halfway through a transmission fluid service on my xkr, including the mechatronics. The car was started yesterday and ran for 20 or so minutes to heat the fluid before draining. Then I replaced the valve body seals in the mechotronic etc. Today I decided to finish the job and do the fill. Yeah right.

Now that everything is buttoned back up, I go to start the car to get the fluid up to temp and run through the gears, and the car doesn't even try to crank. Ignition turns on. Brake pedal mashed to the floor. No crank.

I ran SDD test for start authorization and the only unusual thing was that it was reading 0V on the battery. Which it is obviously not, and I have my 15A charger connected the whole time. Battery might be old (3.5 years, always on a tender) but surely it should read something right?

That sounds like a burned out module. But how do I go about testing which one?

 

Check battery voltage directly from the battery, with both leads disconnected. It has to be 12.6 volts minimum or it's junk. Test that first before doing anything else. Even if it's under 10 volts, it probably won't last long after being fully charged again.

 

I will try swapping an almost new H8 battery I have for another car and see, but it started perfectly and ran for 30 minutes yesterday to warm up the trans fluid. And today, no crank

 

I would check if any of the fuses are blown. When I did the transmission service, it only took less than a couple of minutes before the temperature got to 35-40DegC to check the correct oil level, granted the ambient temperature is 20degC.

 

Just tried a brand new H8 battery. Nothing. Ignition, but no start.

I do get random codes all over the place for missed communication. Something here is fried and I don't know what

 

Checked all fuses, all good

 

Check the ground point where the negative cable connects away from the battery??? There are a bunch of other ground points that could all be checked. I don't rightly know where they are though.

 

Checked those, all good, from what I can see.

Is there any thing at all in the transmission that would cause this? No TCU codes. I replaced the mechatronics, but I'm sure the cable you unplug is in there properly

 

Missed Communication can be caused by low battery voltage. You never said if you checked that voltage or not, it is quite critical. Just because your 'new' H8 battery is in and 'new' doesn't mean it has sufficient voltage.

 

I assume you put the valve body solenoids back in the right order and correct position? If the transmission is in gear car will not start.

 

I actually didn't remove the solenoids, just the entire unit to replace seals. I bet the mechotronic connection is not seated now that I think about it. It is so tight and there's so little room to work there with the exhaust

 

yes the electrical plug is pretty tight, you need small hands to get to it without dropping the midpipes.

 

I took another transmission fluid shower and redid the service. Paid special attention to the position of that gearshift piston on the LHS (not sure exactly what it's called) and making sure it was in the proper slot. Also, lots of care taken to making the mechatronics sleeve fit back in as best as possible. I put everything together, fill fluid until it drips out, and now the car starts as if nothing was ever wrong.

Of course, problems weren't over yet, as the car wouldn't go into reverse on the "walk the gears" part of the fill. I had filled until the fill hole overflowed, but apparently that wasn't enough, as I had to put more in. Ran the car, still not enough, but it did actually stay in reverse for a second. Third time fill until overflow, and finally I can walk the gears with no errors. Filled to overflow, scorch my hand against a 220C exhaust pipe getting the fill plug back in, done.

So it was something in the transmission service that caused the car to freak out on startup and throw all kinds of weird codes. Serves me right for "fixing" something that had no issues in the first place. ~65k miles and my pan was original (dated 2007), rubber sleeves all fine, o rings fine, no metal in the pan magnets, fluid was still colored.

 

[QUOTE=silvertonesx24;2514911................... Serves me right for "fixing" something that had no issues in the first place. ~65k miles and my pan was original (dated 2007), rubber sleeves all fine, o rings fine, no metal in the pan magnets, fluid was still colored.[/QUOTE]
You may have averted replacing that trans in another 30,000 though. Clutches and bands and all that stuff can go bad in a second.
Kudos to you for finding and repairing a problem, especially such an involved repair. It's also a great lesson for others...... TIGHTEN THAT PLUG!!!

 

True, it's just frustrating to give yourself a bunch of work on a car that was shifting fine! Just figured at 65k miles, that is what people recommend, so it would be a good idea to get done. Now on to coolant flush

 

Glad you sorted it out.

When we had our BMW 3 series which had the same 6 speed ZF trans. At 200k km, we had the common issue with the electrical sealing sleeve weeping oil.
The seal kit came with the square seal, as well as the valve body seals. On inspection these seals were in great shape since the kit came with the seals we change them anyway.

I did change the transmission filter and oil at 100k km to Amsoil transmission ATL which meets the Shell M1375.4 specification. At 200k km when changing the seal we change the trans filter and again used Amsoil.

I sold the BMW to a family friend who's daughter uses to go to university. The car has done over 350k km and the transmission is still shifting smoothly and no leaks.

With our XKR I just did a 3 x drain and fill and the transmission filter change with Amsoil transmission oil at 85k km. I'll change/inspect the seals once I hit 200k km or if I'm getting weird shifting. At the moment the transmission is shifting so smooth.