06 February 2024
Our experts advice on Automatic gearbox use and diesel particulate filter problems
Using the Discovery Sport’s auto ’box
I have an 18-reg Discovery Sport automatic (and a 90 Tdi). With the Discovery Sport, when I’m stopped at traffic lights etc, should I leave it in gear with the foot brake on, in neutral, or in park mode?
Which of these modes would be detrimental if I were shunted from the rear, and technically detrimental to the transmission?
Paul Irving, Tarporley
Ed Evans replies: When waiting at traffic lights many drivers leave the gear selector in Drive and hold the car on the footbrake on the assumption that they will soon be moving off again. It’s the same in a stop/start queue of traffic which is edging forward every few seconds.
This is convenient and doesn’t harm the vehicle. However, if you are shunted from behind hard enough to cause your car to roll, the shock and movement will be transmitted from the wheels, through the driveline to the gearbox, potentially causing damage. Of course, you’d be holding the vehicle on the footbrake so, in theory, your wheels shouldn’t rotate, but shock will still be transmitted.
A particular risk when holding the vehicle stationary on the footbrake with the gearbox still in Drive, is that a car running into you from behind could cause your foot to come off the brake pedal as you recoil from the impact, then your vehicle will drive forward, perhaps into the next vehicle, or worse. This could be particularly dangerous if waiting in the centre of a main road to turn right, especially if the steering wheel is turned to the right in readiness – if your foot came off the brake in a rear impact the vehicle could drive across the carriageway. For this reason, I always keep the steering straight ahead until the road is clear to make the turn.
The safest practice (and recommended by Land Rover) is to put the gear selector into neutral and apply the park brake. There will be less chance of a rear impact damaging the auto ’box, and the vehicle will remain braked. There is the slight inconvenience of having to reselect Drive and release the park brake when the lights change, but most electronic park brakes release automatically when driving off.
Unexpected medical issues do happen, if rarely, and any driver can be rendered momentarily confused or injured by an impact, or simply distracted, but if the gearbox is in neutral and the park brake on, then everything is safe regardless of the condition of the driver.
TDCi Defender needs regular re-gen
My husband and I both have Defenders. Mine is a 2012 TDCi and I am frequently having to take it to the dealer to get the exhaust filter cleared. Is it a common problem with the newer Defenders?
I must admit I don’t do long journeys, only once a year which normally results in having to limp all the way home doing about 45mph.
By the way, I have just been driven in my friend’s Grenadier – it’s a beautiful motor, but my heart still belongs to Land Rover.
Martin Domoney advises: What you’re describing is fairly common on vehicles that don’t do long journeys, as the filter doesn’t get hot enough to burn the particulates off. There are two types of DPF regeneration – passive and active, and both require the DPF filter in the exhaust to reach a certain temperature (around 600°C) and maintain that temperature for a set length of time in order for the accumulated particulates (or soot) to be burned off either naturally (passive regen) or with help from increased fuelling and engine timing adjustments by the powertrain control module (active regen).
If the DPF never reaches this temperature threshold – which is common on vehicles that are only used for short journeys and aren’t driven on faster roads regularly – then the DPF never gets a chance to burn the soot off, and so the PCM trips into a safe mode before the filter becomes completely full to prevent damage. This is more than likely what you are experiencing when you take the Defender for a longer drive – the filter is already too full for a passive or active regeneration, and must be forced manually using diagnostic software, which is more than likely what your dealer will be doing.
It’s also worth noting that diesel particulate filter issues can be caused by a problem elsewhere in the emissions system, so it’s worth having a full health check done to rule out temperature and pressure sensor problems, exhaust gas recirculation hiccups, boost leaks and other potential issues. But, by the sounds of things, your Land Rover needs to stretch its legs more regularly, then the dealer visits will be cut down dramatically.
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