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Nissan Sentra Failed EGR Functional Test What could be Wrong?

I own a 1994 Nissan Sentra. It has repeatedly failed the EGR Functional test and the technician has written "failed EGR Functional Test (No Signal)" on the form. I have replaced the EGR valve itself, the EGR solenoid valve, and all of the hoses in the EGR system. I did a functional test on the EGR BPT valve as illustrated by the repair manual (apply vacuum to port, check for air passage through valve) and it seemed to be working. Possible issues: The wire leading to the solenoid valve is kinked back around a cable holder and may be damaged. I have not checked that the temperature sensor is working (do modern models using a solenoid valve still use temperature sensors?). It is possible that I have not connected to hoses to the correct ports, and this could be causing the problem. (i.e. should the vacuum to the EGR BPT valve from the solenoid valve be open or closed when the solenoid valve is energized?) Is it possible that there is a clog in the vacuum manifold port before the vacuum even reaches the EGR Solenoid Valve? My main question is this: What could be wrong having tested and replaced the components mentioned, and how would one go about troubleshooting and fixing it? Best Regards and Thank You Forest

Answer:

You're going to want to start from the top. Inspect for manifold vacuum reaching the EGR solenoid first. Regardless of engine idle speed, you should see vacuum at this port. Next raise idle to around 2000 rpm and inspect for vacuum passage between the lower solenoid ports. The solenoid should be energized open and vacuum should pass through the valve and reach the top port of the Backpressure Transducer Valve. Your Nissan BTV should be marked with an arrow indicating the flow of vacuum. To test the BTV by itself apply vacuum to one top port while at the same time applying pressure to the lower port. The BTV should open and allow for greater vacuum to flow through the valve. Your Nissan Sentra is equipped with an EGR Temperature Sensor which is used by the ECU to verify EGR operation. It may, if faulty, cause the ECU to stop EGR solenoid operation. Check for brittle, disconnected vacuum hoses. If this Nissan has had previous owners check that no one in the pass blocked any EGR hoses (placing BB inside vacuum line - impossible to detect visually). If you suspect faulty EGR solenoid test it by applying battery voltage and check from clicking sound. Solenoid should open and vacuum should pass through lower ports. If you suspect faulty EGR solenoid wiring harness... check for voltage at ECU terminal 105 and ground. While the engine is at 2000 RPM you should see battery voltage at the terminal. Trace the voltage to the EGR solenoid harness. posted by SmogTips Support

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