Discovery TD5 auto box problem

Hi I’ve just got back into the landrover scene I have a discovery td5 and the gearbox seems to be doing some strange shifting, I’ve had nanocom on it and it’s coming up with code P0721 only every now and then it’ll go into limp mode too with M S lights on it also seems to be revving a fair bit more than I’d like while driving.

I’ve done the obvious filter change and fluid x3 color is fine

Nanocom specifically lists code P0721 downshift safety monitoring I haven’t been able to find out much about it hopefully someone can help me out thanks

Done the stall test?

Stanleysteamer said:

Done the stall test?

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Hi, yes forgot to mention that it stops at 3000rpm is that anything to be concerned about?

Landrovermad689 said:

Hi, yes forgot to mention that it stops at 3000rpm is that anything to be concerned about?

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That's a llittle high, could mean the box or the pump to the convertor needs attention. Should be 2600 to 2800.

Interesting read.


Start with the easy stuff.
You don't say how long you have had it or mileage.

J

Stanleysteamer said:

That's a llittle high, could mean the box or the pump to the convertor needs attention. Should be 2600 to 2800.

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Okay where is the pump to converter located? Is it easy to find? It changes into every gear fine including lock up. I will try another stall test later.
EDIT: there are 2 wires with spade connectors underneath near the gearbox one black wire and one green and black near the linkage for XYZ anyone shed some light?

marjon said:

Interesting read.

P0721 code — how to fix error fast | REREV

Discover the importance of understanding the P0721 code for optimal vehicle durability, gaining insights into its significance.

rerev.com

Start with the easy stuff.
You don't say how long you have had it or mileage.

J

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Hi i bought it about a month ago it’s on 148k it’s a y reg

Landrovermad689 said:

Okay where is the pump to converter located? Is it easy to find? It changes into every gear fine including lock up. I will try another stall test later.
EDIT: there are 2 wires with spade connectors underneath near the gearbox one black wire and one green and black near the linkage for XYZ anyone shed some light?

Click to expand...

As far as I know the pump is behind the convertor i.e. when you fit the converter it has be ensured that it meshes correctly with the pump, but I think the pump maybe in the box itself.
Like most humans I have never stripped down an auto box. So it would not be get-atable without removing the box, and digging further.
Are the two wires connected to anything or just hanging loose?
When it comes to anything electrical or to do with ECUs etc @sierrafery is the dude!

Landrovermad689 said:

the gearbox seems to be doing some strange shifting,

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Landrovermad689 said:

It changes into every gear fine including lock up

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So it shifts strangely but fine.

I think this is an electrical problem althought the stall test is a little worrying.
According to the link it looks like the output shaft speed sensor may be one possibility.
Limp home is the gearbox ecu protecting the rest of the vehicle.
My knowledge of all this is limited so I'll jump off and leave it to those who know more.
Best of luck.

Stanleysteamer said:

As far as I know the pump is behind the convertor i.e. when you fit the converter it has be ensured that it meshes correctly with the pump, but I think the pump maybe in the box itself.
Like most humans I have never stripped down an auto box. So it would not be get-atable without removing the box, and digging further.
Are the two wires connected to anything or just hanging loose?
When it comes to anything electrical or to do with ECUs etc @sierrafery is the dude!

Click to expand...

Just hanging loose look like they should be connected somewhere though

Have you driven one before?

If not here goes.

They are not that well controlled, when cold slow to react, the ECU is a bit pants, does get reluctant to change gear. Feels a generation behind the better contemporary longitudinal autos such as the same era GM boxes.

One trick I have is always reverse into the parking spot and drive out, makes gearbox switch errors less likely.

They do rev a bit.

My stall speed is higher due to remap!!!!

Landrovermad689 said:

Okay where is the pump to converter located

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between the bellhousing and the box itself.

not easy to get at and it’s a box out job.

J

MJI said:

Have you driven one before?

If not here goes.

They are not that well controlled, when cold slow to react, the ECU is a bit pants, does get reluctant to change gear. Feels a generation behind the better contemporary longitudinal autos such as the same era GM boxes.

One trick I have is always reverse into the parking spot and drive out, makes gearbox switch errors less likely.

Click to expand...

Yes I’ve driven an auto one before but it was a 300tdi it just seems to be revving too much when in gears when I kick down it seems to struggle which gear to find then m+s flashes that’s when I get the code as soon as I clear it it’s okay until I do it again. I think it’s been remapped as boost pressure is 1.3 bar?

Landrovermad689 said:

Just hanging loose look like they should be connected somewhere though

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Right well I'll stick my neck out and ask if there looks like a connector it should/could be connected to. if it will plug in then maybe it should as they tend to make them all so they can only be plugged into the correct other connection. It could be something as simple as the reversing lamp but then that is me thinking old skool as usual!!!
If you have the RAVE manual then the circuit diagrams might tell you.

don't want to put too much in the stew, but this may be worth a read too.

Wiring or battery could be?

Search with the following terms

ZF P0721 code either autobox or fault

Do not add Land Rover, nor Discovery

Top two results

Hi the LR description of that code is

"P0721(21)* Downshift safety monitor prevented downshift which would have caused engine overspeed" corroborated with the stall test result above 2800rpm seems very like a clutch slip.... IMO that's what it is, not electrical at all

sierrafery said:

Hi the LR description of that code is

"P0721(21)* Downshift safety monitor prevented downshift which would have caused engine overspeed" corroborated with the stall test result above 2800rpm seems very like a clutch slip.... IMO that's what it is, not electrical at all

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Where did you find the LR description of that code as all over the place it comes up with other stuff?

Lets hope this is it.

Stanleysteamer said:

Where did you find the LR description of that code as all over the place it comes up with other stuff?

Lets hope this is it.

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In the official workshop manual (named formally RAVE):


AUTOMATIC GEARBOX - ZF4HP22 - 24
DESCRIPTION AND OPERATION 44-19
(second from top):



corroborated by the ZF autobox troubleshooting manual so i dont know what "other stuff" did you see: