OBD Diagnostics for Engine Overrun and Fuel Cut Optimization

Engine overrun occurs when a vehicle decelerates while still in gear. During this phase, modern ECUs often cut fuel delivery entirely to save fuel and reduce emissions. OBD engine overrun diagnostics help confirm whether fuel cut strategies are working correctly.

What Is Engine Overrun?

How Overrun Happens

Engine overrun occurs when:

• Throttle is released

• Engine RPM remains above idle

• Vehicle momentum drives the engine

Fuel Cut Strategy

The ECU temporarily stops fuel injection to:

• Reduce fuel consumption

• Lower emissions

• Improve engine braking

How OBD Diagnostics Monitor Overrun

Key Parameters

• Injector pulse width

• Throttle position

• Engine RPM

• Fuel flow status

Common Issues Detected

• Fuel not cutting during deceleration

• Throttle sensor errors

• ECU calibration problems

Benefits of Overrun Monitoring

• Improved fuel economy

• Reduced brake wear

• Better downhill control

• Lower emissions

Conclusion

OBD diagnostics confirm efficient fuel cut behavior during overrun, helping drivers maximize efficiency.