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Tim in Scotland

Member Since: 23 May 2007
Location: The Land that time forgot
Posts: 3753

Engine fault warning when tyres are aired down

I was down in the Lakes over the weekend driving a series of green lanes in my D240 First Edition with two D250 110s. - one an HSE and the other a SE.
I was on 20” Duratracs on OEM alloy wheels, one D250 was on 18” Steelies with Maxxis AT’s and the 3rd 110 was on OEM 19” alloys with the factory GoodYear Adventurers fitted. As an experiment the 110 on 19’s aired down from normal 34/37 psi to 28psi all round. As soon as the car drove off it had an engine fault red triangle flag up on the dash as well as the TPMS flagging up low pressures. The car was perfectly drivable with the tyres aired down and there was no limit to engine revs. As soon as the tyre pressures were pumped back up to the normal light load settings on the road the engine fault warnings disappeared from the dash.
So what happened?
Does airing down effectively change the gearing to the extent that the engine management system thinks it’s got a problem?
Is there a tie-in between TPMS and the engine management system so a low tyre pressure also flags as an engine fault warming?
Is this something peculiar to the 6 cylinder diesels?
I haven’t been able to find any reports of this here or on any of the FB groups I’m on with the American guys who seem to think airing down is part of going off-road as it has never been reported - maybe because they are using wheel/tyres without TPMS fitted?

Any suggestions on the above (apart from not to air down when off-road!) are welcome. Theories please! Pangea Green D250 90 HSE with Air Suspension, Off-road Pack, Towing Pack, Black Contrast roof , rear recovery eyes, Front bash plate, Classic flaps all round, extended wheel arch kit and a few bits from PowerfulUK Expel Clear Gloss PPF to come
2020 D240 1st Edition in Pangea Green with Acorn interior. Now gone - old faithful, no mechanical issues whatsoever ever but the leaks and rattles all over the place won’t be missed!

23rd Aug 2021 8:59am

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