there is an error code list in the operation and maintenance manual of your truck, and on your truck, an e-26 refers to the heated oxygen sensor malfunction. what it means is the sensor is reading out of range some times, what makes an O2 sensor read out of range can very often be, and troubleshooting should start with, a good tune up. please only use O.E.M., not 'aftermarket will fit', spark plugs in these motors, as you may know the next person that has to remove the wrong plugs.