What is an indication that the EGR system may not function properly?

The EGR (Exhaust Gas Recirculation) system is designed to reduce nitrogen oxide (NOx) emissions by recirculating a portion of the exhaust gases back into the engine's intake. If the EGR system is not functioning properly, it can lead to several performance issues that can be indicators of its malfunction.

Increased engine temperature occurs because the EGR system helps control combustion temperatures. A faulty EGR can lead to higher combustion temperatures, potentially resulting in engine overheating. Poor fuel economy can arise since a malfunctioning EGR may not provide the necessary exhaust gases needed to optimize combustion efficiency, causing the engine to consume more fuel. High emissions are another sign of EGR issues, notably elevated NOx emissions, because the system is not effectively recirculating the exhaust gases as intended.

Therefore, an indication of an ineffective EGR system can manifest through all these signs: increased engine temperature, poor fuel economy, and high emissions, which supports the conclusion that all of these factors are related to EGR system performance.