Systems and methods for SCR feedgas diagnostics

An exhaust aftertreatment system comprising:

• an oxidation catalyst positioned upstream of a selective catalytic reduction catalyst;
• a doser fluidly coupled to the oxidation catalyst;
• a first sensor for measuring a first temperature of exhaust at a first location upstream of the oxidation catalyst;
• and
• a controller programmed to:
• determine a space velocity value of the exhaust in the oxidation catalyst;
• determine an estimated exotherm value of the oxidation catalyst based upon the first temperature and the space velocity value;
• instruct the doser to insert hydrocarbon in the oxidation catalyst;
• determine an in-use exotherm value of the oxidation catalyst upon insertion of the hydrocarbon into the oxidation catalyst;
• and
• determine a fault condition of the oxidation catalyst based on a comparison of the estimated exotherm value to the in-use exotherm value.