Disco 4 (LR4) U0421 Advise Please

Hi all, back again with my LR 4 air suspension problem. have replaced the air compressor and was getting cross articulation, have just replaced the rear valve block. [ L R dealer had diagnosed the problem with the rear block] Got around 100ks before the U0421 code reared its ugly head again, ride control module [invalid data recieved from ride level control module] have pulled the fuse to disable the suspension but pain in the butt having to do so when I use the car. Any thoughts on the matter?

Hi, what code reader do you have? according to the WSM that code should have associated some other code stored in the suspension ECU which will lead you to the answer but a generic scantool can't access that module directly.
U0421-68 - Using the manufacturer approved diagnostic system, check the air suspension control module for related DTCs and refer to the relevant DTC index

ICarsoft Pro, replacing the ride control module with a refurbished one from the UK, hopefully it will work,

LenV said:

Hi all, back again with my LR 4 air suspension problem. have replaced the air compressor and was getting cross articulation, have just replaced the rear valve block. [ L R dealer had diagnosed the problem with the rear block] Got around 100ks before the U0421 code reared its ugly head again, ride control module [invalid data recieved from ride level control module] have pulled the fuse to disable the suspension but pain in the butt having to do so when I use the car. Any thoughts on the matter?

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hi mate

hope u don’t mind me asking but when u fitted a new compressor was it like for like , if not did u update the software and fit the new relay that should of come with the new compressor plse

in normal ride height did u check the height measurements to ensure they we’re correct plse, , u might have to re program the new second hand module as well

have u ensured nothing had been spilled on the traction control dial as in rock crawl mode that activates the cross articulation

lastly , please double check ur battery when the engine is off so ur reading a min of 12.6 Vdc as indeed a low battery will cause havoc

hope u get on ok

Been away for Xmas so a bit late with the info if you still need it. Replaced compressor with the Japanese made one [not China built] took an hour and a bit, also the relay. Went Ok and works well. Other problems have appeared, trouble with the ride module, so have a second hand one from the UK to fit when I can find out where it goes. So it goes on and on.

LenV said:

Been away for Xmas so a bit late with the info if you still need it. Replaced compressor with the Japanese made one [not China built] took an hour and a bit, also the relay. Went Ok and works well. Other problems have appeared, trouble with the ride module, so have a second hand one from the UK to fit when I can find out where it goes. So it goes on and on.

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that’s ok, we will send u to the naughty step and then ur have to do lines , “ they shall not be late ! Snigger , Lmao

good to hear from u mate , hope ur keeping well , great you’ve got a new compressor , do u remember the make of it please , was it an hitachi and if so is hitachi also selected when u look at the live data plse

yes please regarding what the ride heights are in MM when normal ride height is selected ,

does the disco drop at all when left overnight plse

With the steering wheel is dead straight what is the % angle please in the live data plse

the suspension module if I remember rightly is tucked up behind the dash board, , drivers side by the A pillar , roughly level with the instrument panel

is that the only code u still have

apologoses for all the questions

Hitachi compressor, ride height is OK at [normal 84mm] haven't looked at the steering data and the rcm is of course impossible to access,
After all, it's a Land Rover. Also, I am on the third A/C pipe breaking on the compressor, cost so far for the first two $3200, next one is
due to be fitted on the 10th January. Any idea of why L R dealer next door uses the A/C bloke for all problems and have no idea? Happy New Year.

LenV said:

Hitachi compressor, ride height is OK at [normal 84mm] haven't looked at the steering data and the rcm is of course impossible to access,
After all, it's a Land Rover. Also, I am on the third A/C pipe breaking on the compressor, cost so far for the first two $3200, next one is
due to be fitted on the 10th January. Any idea of why L R dealer next door uses the A/C bloke for all problems and have no idea? Happy New Year.

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many thks , ant that the truth with regards to the lack of access lol, , however I must confess have seen some owners get access to the RCM, think it’s held on with a few bolts to then allow u to remove it , but of course haven’t done this myself, only going on what other owners have said

also trying to remember where the compressor connectors are hidden inside the engine bay on a D4 , think they might be behind ur drivers side headlight but can check if u haven’t found them yet as know there can be issues at these connectors

Apologises as the only ride heights I know are from the centre of the wheel to the bottom of the wheel arch liner , in normal ride height, front 466mm rears 485mm ,

also heard that where dealers sometimes outsource some of there work , yikes regarding the cost of the ac pipe labour and indeed curious why they keep breaking , wonder if the pump bushes are excessively worn and causing vibration causing them to break ?

Can u remember which pipe it is plse as might be able to find out any references to it for u

Plse let us know when u get chance of the other readings, ie , steering wheel angle sensor , note that these can sometimes come lose on the column causing untold issues and dashboard lights

Plus just thought with regards to doing a basic OBD2 test , just trying to save u some time in having to mess around with the suspension module by using a multimeter

Also before doing the test would u be so kind to check ur batter voltage plse , with the engine off and then with the engine running , don’t think u have stop start with the year of D4 u have, thks

fingers crossed the suspension module is ok and won’t have the hassle of programming in the replacement module

hope it’s useful to u


With both battery leads disconnected from the battery posts

Multimeter set to ohms, ( TP Is just short for test probe from ur multimeter)

TP to pin 6 other TP to pin 14 , read ohms

TP to pin 3 other TP to pin 11, read ohms

Reconnect battery, ign off , meter set to Vdc

TP to pin 6 other TP pin 4 Read Vdc

TP to pin 6 other TP to pin 5 Read Vdc

TP to pin 14 other TP to pin 4 Read Vdc

TP to pin 14 other TP to pin 5 Read Vdc

Third main compressor pipe fitted [ 7hrs labor plus pipe at cost [$890] I have used a stainless hose clip to secure it against the steering hose metal
part to stop vibration. {New compressor fitted, start of problems] Have got a replacement ride module from Gentlemen of Salvage in Devon, Bast--d
of a place to access under the dash. Have fitted it but it needs to be programmed of course by Land Rover dealer, replaced it with the original and
Unbelievably it is back to normal! The trouble is I don't trust it as I want to sell the car. Will take the advice of a particularly good mechanic and swallow
my pride and buy a Korean Kia. 7 yr warranty and they can do most of the work without going back to a dealer. I have attached a photo of a broken pipe. Cheers