C5 Automatic gear issue

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zeeshanzaki
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C5 Automatic gear issue

Post by zeeshanzaki »

The automatic gear does not engage after stopping at traffic light. All the gear work work fine in manual. But if i put in auto mode, sometimes it does not engage gear. It looks like when the car stops, the gear stuck in 3rd dear and does not downshift. There was fault P1728 which I cleared using lexia. Still has issue, but no error code yet. From the service history, the transmission was never been serviced. What could be the problem?

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xantia_v6
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Re: C5 Automatic gear issue

Post by xantia_v6 »

Is this a C5 with ES9J4S engine and 4HP20 transmission?
Are there no fault codes recorded in the transmission ECU?

zeeshanzaki
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Re: C5 Automatic gear issue

Post by zeeshanzaki »

Yes it is 4HP20. These were the fault code before clearing:
Permanent Fault, CAN Engine torque information
Code: P1728
It also pops up ESP related fault along with transmission fault. But when I went into detail of this fault there was nothing to clear.
When it hesitate to engage gear when take off, i switch to manual.

It also used make noise when cold in transmission area.
Last edited by zeeshanzaki on 17 Jul 2020, 03:08, edited 1 time in total.

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xantia_v6
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Re: C5 Automatic gear issue

Post by xantia_v6 »

The symptoms seem fairly consistent with a blocked transmission oil filter, which starves the pump and reduces the available pressure to the point where the transmission cannot work.

It may be something else, but I would be preparing for the worst.

Unfortunately the oil filter cannot be changed without removing the transmission (and probably the engine) and splitting the transmission casing, assuming that there is not yet any secondary damage.

zeeshanzaki
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Re: C5 Automatic gear issue

Post by zeeshanzaki »

So if it is blocked filter then changing oil won't help.

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xantia_v6
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Re: C5 Automatic gear issue

Post by xantia_v6 »

zeeshanzaki wrote:
17 Jul 2020, 03:08
So if it is blocked filter then changing oil won't help.
No, an oil change won't help if it has got to the point where it is not working (assuming that has still got oil in it).

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xantia_v6
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Re: C5 Automatic gear issue

Post by xantia_v6 »

One thing you could try is to simulate an electrical failure by pulling the fuse for the transmission ECU, and see if the car drives OK in limp mode. The transmission will be locked in 3rd gear and reverse, but should at least drive.

If you suspect that a blocked oil filter is the problem, then limit running time of the engine to a minute or two, as the usual next stage in the failure is overheating of the nose bearing on the torque converter which writes off the transmission oil pump and maybe the torque converter.

zeeshanzaki
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Re: C5 Automatic gear issue

Post by zeeshanzaki »

I removed the ecu fuse but car won't start. It was giving esp/abs and immobilzer erros so i reconnected fuse. I notice car changes gear fine but in the 4th gear it makes some noise.
I am also getting tyre punctured error after i disconnected ecu fuse. Its annoying and lit stop light on cluster. How do i remove this error.

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Re: C5 Automatic gear issue

Post by zeeshanzaki »

It was actually a tyre punctured not a false alarm.
Car is driving and changes the gear but not as smooth as before.

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GiveMeABreak
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Re: C5 Automatic gear issue

Post by GiveMeABreak »

^ That's another reason why I think they are great systems - as you cannot visually tell the state of a tyre and can save you from an accident.