i was towing two berth caravan back to liverpool from cornwall,after 8 mile terrano would not get me up first hill! phoned aa he plugs computer in and says it is mass senser,i told him it was replaced 12mths ago,he said it is reading 228 when it should be 28?charges me 109pound and off i go got me 98mile and same proplem!24hours and 5 tow trucks l8ta back home,car still driving ok without caravan anyone help?thanks for any advice.someone said there is a filter the size of a thimble which you can remove?