Q: How do you start car after running out of exhaust fluid?

Hi there. There is a sensor in the diesel exhaust fluid tank that measures how much fluid is in there. This is why the dash can tell you how much fluid is remaining in the tank. The engine will not start up until there is at least 30% of the tank is filled up. The exhaust fluid is to help reduce emissions in the catalytic converter on your vehicle. If there is no exhaust fluid in the catalytic converter, then the O2 sensors will register a higher soot content and shut down the starting circuit. Since you have topped of the tanks and the vehicle still will not start up, then you will need to remove the battery cables from the battery and leave them off for 13 minutes and then put the cables back on. This will clear the computer to analyze the exhaust system for 2 hours. If you need further assistance with your diesel engine not starting after running out of exhaust fluid, then seek out a professional, such as one from Your Mechanic, to help you.