e39 540iA gearbox fault code identifying

[murrama]

My e39 540iA has a problem with the gearbox, in D or S the car will move only slowly from a standstill even if the engine speed increases. If I manually select first or second gear, they will work just fine. If I go into D or S when the car is moving all gears from 2-5 will work just fine and shifting is smooth. The car won't shift from 1 to 2 if I slow down to almost stop. There are no warning lights on the dashboard.

ISTA will show several fault codes like 00006A and 000016 AGS: Transmission control: fault stored
What could this mean?
ISTA 540 gearbox faults.jpg

INPA shows only one code related to the gearbox, ECU GS855:

120 Gear Check 0 (Symptom)
Error frequency : 1

Label byte 21 16.00 -
Gearbox oil temperature 73.00 degrees C (also 19C and 54C after reseting fault codes)
Output Speed 256.00 rpm
Plausability
---
---
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Error present
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I have also once seen 121 Gear Check GLUE0, label byte 35.00, oil temperature 37.00C, output speed 544.00 rpm. But it didn't come back again.


When cold, within 5 minutes from start, if I brake quickly when 2nd gear is selected in manual mode, the gearbox may stay in "neutral" for a while until it catches the gear again and the car starts moving again. When it warms up, I don't have this issue.

Any ideas on where the issue could be?

[JN Garage]

I had a bad TCU DME / module throw all sorts of codes but if its not generating any codes that is an odd one

[Chedley]

When did you last serviced the transmission (fluid and filter) ?
How many miles? Any transmission leaks ?

The transmission fluid level may be low. Check it and top off if not full. Better, service the transmission or at least drain-and-fill with the right fluid (ZF or Pentosin synthetic ATF-1)

[Jaaap]

^^^ What Chedley said: check the basics first.
Also check for leaks down there.

[murrama]

The transmission fluid and filter were changed about 35k miles ago. The car itself is driven about 270k miles. There are no obvious leaks, but the oil was changed by the previous owner so not sure how well it was done. Maybe it would be worth to check it.

[CPHES]

If you have 270k miles on almost any Auto trans, it could be done. I’m guessing it’s a 5hp24 - some early e39’s had the sturdier 5hp30, but you are at the point where stuff happens.

[murrama]

Yes I understand. It's a 5hp24 as far as I know. Would it be possible to know what has gone wrong from those fault codes?

[Chedley]

That INPA error code "120 Gear Check 0 (Symptom)" indicates a bad output transmission speed sensor or signal. The sensor is pretty easy to locate and replace on the 5HP24 transmission. Is it sporadic ? If you erase the error code, does it come back on and stay ?? If it is a one time occurrence, I'd ignore it.

Again, first, I'd make sure the battery is fully charged.
Then I'd check the transmission fluid level, drain-and-refill if necessary. Note that you'd have to drop the transmission oil pan anyway if you are replacing the transmission speed sensor, so...
(See: https://www.rangerovers.net/threads/...ber-drm.41355/)

[murrama]

Thanks, I have searched everywhere but could not find what it means. Where could I find a complete list of the error code meanings? I just wonder why the speed signal would affect only changing from 1 to 2 but not the rest of the gears.

The error code 120 comes back every time after some driving. I will check the battery and fluid level in a few days.

[Chedley]

Well, if the error code 120 comes back regularly, then it is probably a bad speed signal sensor in the transmission. Test it or replace it as indicated in the link above.
Still, first, I'd start with recharging the battery and testing the alternator. So many bizarre and sometimes misleading errors are caused by a low or bad battery...!!

Here is a list of INPA error codes for your E39 540i.