Rick's Free Auto Repair Advice

P0400 Exhaust Gas Recirculation Flow Malfunction Nissan

Owners of 1999 Nissan Altima 2.4L and 2000 Nissan Frontier 2.4L vehicle may encounter a P0400 trouble code with a check engine light. Owners may also notice an engine stall at idle when the vehicle is warm. Before you start replacing parts, learn how the system works and test each component according to this procedure.
Start by checking the rubber hose that goes to the bottom of the EGR back pressure transducer. The transducer measures the amount of “backpressure” in the exhaust system to determine if the EGR valve is operating properly. Because exhaust gas is so hot, it can sometimes burn the hose. A burned hose will cause improper EGR operation. If you find any cracks, holes, or burn marks, replace the hose.

Next, tee in a vacuum gauge to the EGR valve vacuum supply and drive the vehicle until warm. Monitor the gauge to make sure the EGR valve is receiving vacuum. It should be between 2 to 4-in. to be within range. If it is, then move to the next step. If not, refer to the EGR vacuum solenoid check below.
If you have vacuum, then connect a voltmeter to the blue/yellow wire on the EGR temp sensor. Drive the vehicle (with the vacuum gauge still attached) and look for sensor voltage drops to less than 1v. That indicates proper EGR operation. The sensor checks for a temp increase once the EGR opens and exhaust flows. If the sensor voltage drops, then you’re getting EGR flow. If the sensor doesn’t see hot gas, the PCM will set the trouble code.
If you’re not getting vacuum at the EGR valve, check the hoses running between the EGR valve and the EGR solenoid, and the solenoid and the intake manifold. The EGR solenoid receives grounding “pulses” from the PCM. The duration of the pulses determines how long the solenoid remains open, allowing vacuum to flow to the EGR valve. That’s how most car makers regulate the opening and closing of vacuum operated EGR valves.

Get a new exhaust gas temperature sensor here:

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© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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