Rick's Free Auto Repair Advice

P0401 egr insufficient flow detected Honda

P0401 EGR insufficient flow detected

If you own a Honda and encounter a P0401 egr insufficient flow detected, follow these instructions. The P0401 code is defined as Exhaust Gas Recirculation Flow Insufficient Detected. The computer commands the EGR valve to open. An EGR position sensor is built into the valve to detect how much the valve actually opened. If the position sensor results don’t match the commanded value, the computer sets the P0401 trouble code.

The first step is to remove the EGR valve and check the passages for carbon buildup or blockage. If the passages are blocked, you’ve most likely found the problem. Most shops use a speedometer cable attached to a drill to open up the passages while using a shop vac to remove the loose carbon. That’s if the carbon buildup is located on the exhaust port. If the carbon is on the intake port, it’s best to remove the intake manifold and clean it on the bench. Once the ports are clean, re-install the existing EGR valve, clear the codes and test drive the vehicle until it complete a drive cycle. For more on drive cycles, read this post.

If the P0401 egr insufficient flow detected returns, the problem can be a bad EGR valve, bad EGR position sensor, or a wiring problem. Consult a shop manual for the particular wiring diagram for your vehicle. As an example, a 2002 Honda Civic with the 1.7 engine has five wires going to the EGR valve. The blue/red wire carries the pulsed voltage from the computer to open and the EGR valve solenoid. The black wire is the solenoid ground. Three wires go to the EGR valve position sensor. The yellow/blue is the reference, green/yellow reference return, and the while black is the actual position sensor reading.

Using a digital DVOM, backprobe the connector and check for EGR position sensor reference and reference return while the engine is running. EGR position sensor signal and pulsed command can only be checked once the vehicle is in closed loop and running at higher RPMs where EGR would normally be used.

Standard Motor parts sells replacement EGR valve position sensors so you don’t have to buy the entire EGR valve. However, some valves have the position sensor built in, so you must buy the entire valve if the sensor tests bad

Shops are reporting some incidents of wire breakage about 12” away from the connector.

Posted on by Rick Muscoplat


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