Method to control and diagnose an exhaust gas heat exchanger

A vehicle comprising;

• an engine;
• an electric motor configured to propel the vehicle;
• a battery in electrical communication with the electric motor;
• an exhaust heat recovery system for the engine, the system having an exhaust gas heat exchanger, a first temperature sensor downstream of the engine, and a second temperature sensor downstream of the exhaust gas heat exchanger;
• and
• a controller configured to:
• (i) generate a signal to control exhaust gas flow through the exhaust gas heat exchanger, (ii) measure a series of differences between coolant temperature downstream of the exhaust gas heat exchanger and coolant temperature downstream of the engine over a predetermined time period using the first and second temperature sensors, and (iii) generate a diagnostic code based on a comparison between a summation of the series of differences and a threshold.

A computer readable medium having stored data representing instructions executable by a controller to control a vehicle, comprising:

• instructions for generating a signal to control exhaust gas flow through an exhaust gas heat exchanger;
• instructions for measuring a series of differences between coolant temperature downstream of the exhaust gas heat exchanger and coolant temperature downstream of an engine over a predetermined time period;
• and
• instructions for generating a diagnostic code based on a comparison between a summation of the series of differences and a threshold.