Kia sorento with loud banging noise from gearbox area at around 40-50mph,mainly in 4th or 5th gear. Bad enough to hold back vehicle briefly. At lower speeds and gears its possible to drive without issue, but under load it returns at around 50mph. Cant find anything obvious in the prop shafts etc although there is quite a bit of backlash in rear diff. It has had a used front diff fitted at another garage as old one blew up although that all looks ok.I Cant pin down the source of the noise it could be the gearbox or transfer box area.Theres a fault code in the 4wd ecu which is P1739 General position encoder fault.

Colin

I bet it's the model with "auto" 4wd selector and somebody has fitted 20" wheels?
If it is permanent 4wd, all tyres MUST be the same size, brand, type and within 2mm of each other.

The banging is either the transfer case LSD releasing or the low range trying to engage whilst driving.
If you have a scope, you could scope the transfer case front/rear speed sensors to ascertain if the axle speeds are identical.

The 4wd ecu is in the passenger footwell, up against the transmission tunnel (below the carpet).

Tony

Could you remove the front propshaft and road test to eliminate the gear box.
I think it is the Sorrento that you can pull a fuse to stop the 4wd working, on some models the warning lamp will stay on.

Removed the propshaft that drives front axle and the noise has gone, car drives fine-no warning lamps. Looks like the used front axle is faulty. Customer is going to return it to the garage that supplied/fitted it.

Colin

Hi Colin, the front axle probably failed because the 4wd is now fully permanent, instead of being a LSD.... So the transfer case is winding up.

The chances of the front axle being faulty are pretty slim (unless someone has put the wrong ratio diff in, which I doubt), but the transfer case is faulty, or the tyres are too far apart in circumference, causing wind-up, and the banging noise is the centre diff jumping.
I believe there is a place that reconditions the transfer cases at a reasonable price (£700 @ http://www.4x4gearboxes.co.uk/price.php ).

Thanks for the information Tony. It does sound as if the noise is coming from the transfer case area. Does it just unbolt from the back of the gearbox? It all looks like a complete unit.

Thanks

Colin

Yes, if I remember correctly it's only around 6 bolts. Early ones require the gearlever to be removed to get to a hidden top bolt, but all the later ones are straight forward. Drop the centre exhaust makes it easier too. Approx 1.5 hours for R&R. Oil is special though, Kia call it TOD oil (Torque On Demand).

Tony