YACT How do modern engines know when the EGR is bad?

[Analog]

Is it through the EGR itself, or does a downstream sensor know when its not working?

 

[Compton]

I've seen a lot of cars that don't know if its working or not. The TPI F-bodys (MAF) have a temp sensor that screws into the egr valve. When its reading out of range, the ECM assumes the EGR is not functioning properly. I would assume your Fiero might have a similar setup.

 

[Wingznut]

It depends on the yr/make/model of course. But many have a sensor on top of the valve, which monitor the valve movement.

 

[rezinn]

Likely also an EGR diagnostic switch that tests to see if the EGR is opening at the correct times. If it is stuck open during startup or not opening when the ECM tells it to, it will set off a check engine light.

 

[blahblah99]

EGR temperature sensor? If its stuck close, then the sensor will sense ambient temp, and not the hot gases.

 

[Viperoni]

On my topaz, there was a sensor that sensed exhaust flow through the tube that connected to the EGR valve. Then another actuator controlled how much engine vacuum the EGR valve saw, so that's how the computer controlled how much exhaust gas got back into the engine.

I would throw a code for Insufficient EGR flow when I had my complete exhaust system and a higher flowing MAF.

But yeah, each EGR system works differently.

 

[Quixfire]

Most modern cars and trucks with an On Board Diagnosis II (OBDII) system monitor EGR operation with a system similar to the one described below.

Exhaust Gas Recirculation (EGR) System Monitor?Differential Pressure Feedback EGR
The Differential Pressure Feedback EGR System Monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Input from the ECT, CHT, IAT, TP and CKP sensors is required to activate the EGR System Monitor. Once activated, the EGR System Monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR System Monitor tests are also performed during on demand self-test.
1. The differential pressure feedback EGR sensor and circuit are continuously tested for opens and shorts. The monitor looks for the Differential Pressure Feedback EGR circuit voltage to exceed the maximum or minimum allowable limits.

2. The EGR vacuum regulator solenoid is continuously tested for opens and shorts. The monitor looks for an EGR Vacuum Regulator circuit voltage that is inconsistent with the EGR Vacuum Regulator circuit commanded output state.

3. The test for a stuck open EGR valve or EGR flow at idle is continuously performed whenever at idle (TP sensor indicating closed throttle). The monitor compares the Differential Pressure Feedback EGR circuit voltage at idle to the Differential Pressure Feedback EGR circuit voltage stored during key on engine off to determine if EGR flow is present at idle.

4. The differential pressure feedback EGR sensor upstream hose is tested once per drive cycle for disconnect and plugging. The test is performed with EGR valve closed and during a period of acceleration. The PCM will momentarily command the EGR valve closed. The monitor looks for the differential pressure feedback EGR sensor voltage to be inconsistent for a no flow voltage. A voltage increase or decrease during acceleration while the EGR valve is closed may indicate a fault with the signal hose during this test.

5. The EGR flow rate test is performed during a steady state when engine speed and load are moderate and EGR vacuum regulator duty cycle is high. The monitor compares the actual Differential Pressure Feedback EGR circuit voltage to a desired EGR flow voltage for that state to determine if EGR flow rate is acceptable or insufficient. This is a system test and may trigger a DTC for any fault causing the EGR system to fail.

6. The MIL is activated after one of the above tests fails on two consecutive drive cycles.

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