OBD II Readiness Monitors

Non-Continuous Monitors

EGR System Monitor

Not all OBD II equipped engines have an EGR valve or EGR system; on those systems this monitor is not used. The EGR system monitor allows the PCM to test the function and the exhaust gas flow through the EGR system. The monitor is activated during EGR system operation that occurs under normal engine and vehicle operating conditions. As with most other monitored OBD II systems, all EGR electrical components are checked for electrical and rationality faults during continuous monitoring.

On OBD II equipped vehicles two main strategies are used to test the EGR system. One strategy uses a temperature sensor to measure exhaust flow through the EGR system when the EGR valve is commanded on by the PCM. With this strategy the temperature sensor signal can also identify EGR flow at times it is not wanted such as during engine idling.

The other strategy used to test the EGR system uses an EGR valve sensor to measure EGR valve position which then infers EGR flow through changes in manifold pressure occurring when the PCM commands EGR flow.

The EGR monitor is performed during driving. The PCM enables the flow rate test of the EGR system monitor after the vehicle is maintaining a steady speed above 25 mph and the EGR valve is commanded on. For the monitor to run, the check engine light needs to be commanded off by the PCM and the continuous monitors must have completed successfully.

The PCM will successfully complete the EGR monitor if the proper flow of EGR is detected and no EGR flow at idle is indicated. If the flow rate detected is too low or too high or present at idle the PCM will set a pending code. The PCM will command the check engine light to illuminate and store a DTC if the fault occurs during 2 drive cycles.