Gearbox oil temperature sensor G93 crazy behaviour -- need a bit a help

[notorious]

Hello everyone.

My D2 3.7 gearbox code FBB developed an interesting problem.


Symptoms:

After about 30min-45min minutes of driving it changes shifting strategy from fuel 'economy mode' into 'aggressive' kind of 'sports' mode. It basically downshifts abruptly and never upshifts back again. Releasing gas pedal completely doesn't help.

Example: If I drive on highway on 5th gear @ 70mph @1500rpm all of a sudden the gearbox shifts to 3rd gear and just continues to drive on 3rd gear @70mph @3500 rpm. Releasing gas completely doesn't help to upshift back again. The only way to go to higher gear is to press gas to rev the engine till 4000-4500 rpm and then it will upshift, but only to 4th gear. This behaviour is similar to the sport mode, but of course I don't select the sport mode.

I can override this by putting gearbox into tiptronic mode and manually selecting the 5th gear and continue my journey. But as soon as I disengage the tiptronic mode the behaviour gets back to the downshifted 'aggressive' mode.

The behaviour will terminate as unexpectedly as it came. Sometimes it will last for about 30 minutes of driving and then disappears without a trace. Sometimes it will last for only several seconds -- you drive as per normal, then suddenly it shifts couple of gears down, engine revs, then in 3 seconds it is all gone, back to normal gear -- driver didn't do anything! :^)


Analysis:

I connected VCDS and started to look at gearbox oil temperature sensor reading (that's measuring group 7, field 1). That sensor is called G93 and it is part of the electric harness that feeds valves. It sits in the sump.

When I come to cold car in the morning the sensor shows 28C when the ambient temperature sensor on the dash shows 14C. Weird.

So I start driving. The temperature slowly raises to 78C-80C and stays there.

After about 30 minutes of driving, out of the blue the sensor jumps from 80C to 155C within about 2 seconds and then stays at 155C. The same moment the crazy mode engages -- the gearbox downshifts and never upshifts back again. Perhaps we should call this mode a 'cooling off' mode? :^)

Interestingly, there is no error logged in the gearbox ECU. Clearly, sensor can't change temperature from 80C to 155C within two seconds. Implausible sensor value should be detected by ECU software and logged as error, but it doesn't happen on my car.

So the G93 oil temperature sensor and the corresponding harness is going to be changed ASAP. That is sump out job.


My ask from you:

Could some of you with D2s cars and VCDS cable measure for me the G93 gearbox oil temperature sensor reading (measuring group 7, field 1) when you sit into cold car in the morning, plus right after you finished 45+ min driving?

I'd like the info in the following format:

1. Cold car before driving:
G93 reading: xxC
Ambient temperature on dash: yyC

2. Hot car after 45+ minutes of driving:
G93 reading: xxC
Engine displacement: 3.7 or 4.2

In terms of hot temperature reading I'm specifically interested in D2 cars with 3.7 engine. These engines come with gearboxes with separate oil coolers, which are not present on cars with 4.2 engines and S8, so they *can* run at lower temperatures. If your car is not 3.7, but you are willing to publish your readings here please specify your engine displacement.

The most important reading for me is the cold reading, so if you can publish at least that one together with your dash ambient temperature reading I'll be equally grateful.

Many thanks.

[The_Laird]

Yes, with a bit of help from David (who has the VCDS just now) I could do the cold temp this weekend and the 45 minute drive temp on Monday if that's any help

[David's8]

..and as I havent got a car at the moment (still in garage, having belt/seal/exhaust done), I will return VCDS to the Laird.

[notorious]

About G93 sensor from here: http://vwts.ru/pps/pps_951903_01v_01...ssions_eng.pdf



TCC = Torque Converter Clutch

[moltuae]

I only have an older VAGcom 3.x presently, so hope this helps.

I was on my way out to the car to check/clear codes when I saw your post, so I grabbed a screenshot:

(cold engine/box)




The temperature reading on the dash was 14 degrees C.





Sounds to me like you have a connection issue, perhaps one that is common to both the sensor and the selector.

[notorious]

Cheers Mark.

16C is very close to 14C. You're in good shape!

[The_Laird]

OK, done.

At cold, the oil was 17C with an outside temperature of 14.5C.

We did a total of about 22 miles on a mix of dual carriageway, B roads and around town. Outside temp ranged from 13.5 to 14.5 and the oil temp from about 74C to a max of 84C when I stopped after the run.

Hope that is of some help Sergey.