Q: Diesel particulate filter warning light is on.

Hello, The DPF light relates to the diesel particulate system in your vehicle which includes a filter in the exhaust system that is designed to capture excessive soot and carbon that is a bi-product of the diesel combustion process. Over time, this filter will build up with excess soot and carbon deposits. Diesel engines are designed to combat this by raising the exhaust temperatures to burn off the excess buildup as you drive at higher speeds. This is called passive regeneration. When the light comes on, this means that the soot levels have reached a critical point (usually around 45-50%) indicating that the system needs to burn off this excess buildup by taking the vehicle on the highway and driving at speeds above ~40 mph or more which will help to raise the exhaust gas temperatures to burn off the excess build up. If this light is ignored and the driver continues to drive at lower speeds, this may cause the computer to put the vehicle into a "limp mode" in an effort to prevent further damage to the exhaust filtering system. It sounds like this is what has happened in your case. I would suggest having a professional from YourMechanic come to your location to take a look at your vehicle.