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Old 25th March 2020, 06:26 PM
think_or_thwim think_or_thwim is offline
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Default P0721 and engine shuts down

Guys, cars been a beauty and now throwing a tizzy fit..

Car fires up fine and then engine shuts down and throws this code.. where the heck is the Output Speed sensor please??

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Old 25th March 2020, 06:47 PM
MikkiJayne MikkiJayne is offline
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I take it you're scanning with something generic and not VCDS?

The transmission output speed sensor to which 'P0721' allegedly refers is inside the gearbox, and it would cause the gearbox to go in to limp mode when in attempting to move in D or R. It would not shut down the engine.

Which module are you scanning to find this code?

Does the engine start and immediately shut down or does it run until you do something?

The usual cause of starting up then immediately shutting down after a couple of seconds is an immobiliser fault. What year is the car?
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Old 26th March 2020, 07:19 AM
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johnny_quattro johnny_quattro is offline
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Clipped the following from the documentation listed here on the site:

Fault code 17105 / P0721
Display on -VAS 5051-
17105 / P0721
Gearbox output speed sender -
Implausible signal
Possible cause of fault
How to rectify fault

♦ Open circuit or short to earth or – Read measured value block
positive in wiring to component
001: With hydraulic control
“Type E17” ⇒ page 98 , with
hydraulic control “Type E18/2”
⇒ page 112
– Check wiring and connector ac‐
cording to current flow diagram.
Also check connector for con‐
tact corrosion or moisture

♦ Gearbox output speed sender - – Perform electrical check, test
G195- defective
step No. 19 ⇒ page 136

♦ Screening for gearbox output
speed sender -G195- defective

♦ Engine speed signal or gearbox – Rectify fault as described for
speed signal incorrect
fault code 17100 / P0716
⇒ page 41

♦ ATF level not OK
– Check ATF level ⇒ Automatic
gearbox 01V, front-wheel drive
and four-wheel drive; Rep. Gr.
2000 D2 A8L – Audi silver, solar sunroof, heated front Recaros
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Old 27th March 2020, 09:55 AM
think_or_thwim think_or_thwim is offline
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Scanning Engine and TCU...Car will run then just shutting down, bizarre..
All lights coming on the GB gear select panel.. Is pointing at G195 01V927321A which feeds ECU/TCU etc.. Spoke to my Gearbox god here in Cornwall and he also said nothing should shut it down.. Fitted new brake switch and Crank sensor and cleaned up the plugs and contacts around the area.
Removed and cleaned the GB sensor in the LH driveshaft output too,,, all good...
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Old 27th March 2020, 10:50 AM
think_or_thwim think_or_thwim is offline
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Using genuine VCDS and also Launch X431 Pro V4, all up to date and paid for versions, I own a garage www.ubiquemotordiy.com

Got my auto electrician mate on the case, we have also done lots of checks and replaced the fuel pump relay.. This all started when I flipped from Petrol to LPG and car threw N05 coil pack, which happens every so often.. LPG is not associated to this as its been switched off now and cars still randomly throwing this code as the engine has shut down!!

Will check the MBs and see if the sensor loses the signal and then engine shuts down,, hard to diagnose this bugger!!
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Old 28th March 2020, 06:22 AM
spannerrash spannerrash is offline
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As you have already said, the gearbox codes should not shut down the engine. This either suggests you have 2 separate faults with the engine shutting down not logging any codes. So only the gearbox codes are show. Or the fault is affecting 2 separate systems at the same time. Gearbox and engine.

Have you checked for water ingres in the ecu box? Both ecu and tcu are located in the same box. This has happened many times and can be quite a common problem.

Have you tried squirting easy start or some similar solution into the inlet whilst trying to start the car? May at least tell you if the engine stopping is fuel or electrical related.
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Old 28th March 2020, 12:21 PM
B@fink B@fink is offline
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More details might help someone come up with a diagnosis. How long does it run for?When it’s in shut down will it restart straight away? does it take multiple cranks before restart? how much fuel is in it? Can you hear the fuel pump prime at ignition on? Any warning lights? Funny noises? Any other fault codes or just the gearbox one?

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Old 1st April 2020, 12:02 PM
think_or_thwim think_or_thwim is offline
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18169 seems to be the bad boy~!!
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