Autobox rumble

Q

I wonder if you can help me with a number of problems with a 2003 Peugeot 406 2.0 HDI 110 automatic? The first and biggest one concerns the gearbox, which is a four-speed AL4 model.

The gearbox has a very bad rumbling/ grinding noise from speeds of 15mph and upwards – as you drive, it vibrates the car and is very loud at all speeds. I thought it was the front wheel bearings and had both changed, but it made no difference.

I was then told it was the driveshaft centre bearing, as the sound was coming from the middle of the engine when driving. The bearing was changed, to no avail. Now I have been told it is either the differential bearings or pinion bearings. The gearbox changes gear smoothly, could this be the noise that’s vibrating though the whole car?

The second problem is that the engine management light has been going on and off and the vehicle is down on power. When going uphill, it struggles to get up to 40mph with my foot down and it will not change gear, then the EML comes on.

I had a garage read off the fault codes and these were: ‘P0401 turbo pressure sensor’, ‘P0101 EGR Valve’ and ‘P0235 Airflow sensor’. I was told by the mechanic that all three faults will be related and may be due to the airflow sensor being at fault. There were some fault codes on the transmission side and these were: ‘incorrect transmission ratio’, ‘can engine torque’ and ‘kick down switch’. Do you know if these could be related to the noise within the gearbox?

The mechanic said he would be surprised if it was the bearing in the gearbox, as it had not damaged the valve chest and prevented the car from still driving.

Steve Mccreery

A

As you have had the three bearings replaced, I can only assume that the fault is with the gearbox, as you have been advised.

You do not mention if the auto gearbox fluid has been checked or changed, so I would advise you to do this next. The oil level plug is in the base of the gearbox and uses a drainage tube system. If the gearbox bearings are failing to such an extent, I would expect to find the auto gearbox oil has discoloured and contains a silvery residue.

I'd have the gearbox codes read properly and see if they clear, as the electronic systems on the AL4 control many functions and will affect the gear change.

The code ‘P0401’ refers not to the turbo pressure sensor, but to insufficient EGR flow, ‘P0101’ refers not to the

EGR valve, but to the MAF sensor, and ‘P0235’ refers to turbocharger boost sensor malfunction (the same faults just incorrectly assigned). I would clear these three faults, then act upon the first code to reappear. As your mechanic says, the faults may be due to a failed MAF sensor, but the first course of action after rectifying the gearbox problem may be to clean the EGR valve and MAF sensor.