6.7L Power Stroke P0401 Insufficent EGR Flow Diagnostics
A repetitive common issue problem people may need help with on the 6.7L Power Stroke diesel engine is diagnosing a code P0401. This is one of the easier codes that a 6.7L PSD can trigger as there is only a few likely cuplrits causing a P0401. This is what is known as a conditional diagnostic trouble code (DTC).
P0401 Insufficent EGR Flow is a conditional DTC
A conditional DTC is simply a diagnostic trouble code that only sets when certain conditions result in a failure of the emissions test. These types of codes do not set when a hard fault is actually detected, as such with a Hard Fault DTC.
In the case of the P0401, this code is informing you that your exhaust gas recirculation (EGR) system is not operating correctly. The definition of the code P0401 is "Insufficent EGR Flow" which does simply mean the EGR system is not flowing the correct amount of air based on command. The PCM is monitoring flow based on several factors. EGR is important because it is a method for reducing NOX emissions.
Because the P0401 code is a conditional code, the first step in diagnostics is to focus on other hard fault DTCs first. If you don't have access to a fancy scan tool, give this a try FORScan - The cheapest and best scan tool for Ford DIY Mechanics.
Monitoring Exhaust Gas Recirculation (EGR) for Performance
The PCM is looking at several indicators to monitor EGR flow. One such was monitoring the mass air flow of the engine with the MAF sensor. The PCM will look at MAF readings as it opens the EGR valve and compare the flow drop against predetermined levels. The PCM can also open the EGR bypass and monitor the flow difference when the exhaust if flowing through the cooler and when bypassing.
The effectiveness of the EGR cooler can be measured by comparing the EGR temperature with the bypass opened against the temperature with the bypassed closed. There should be a significant difference.
P0401 Symptoms - Check Engine Light, Reduced Power
If you have a P0401 DTC, surpisingly you may only notice the check engine light is illuminated. At face value this doesn't cause many symptoms itself but once the cooler becomes increasingly clogged it can start to cause of issues such as Selective Catalyst Reduction (SCR) codes like the dreaded P207F.
This happens because EGR does reduce combustion temperatures which help to reduce NOx levels in the exhaust.
What causes P0401 code on a 6.7L Power Stroke failures?
Generally when diagnosing any issues a technician will always look at things from the least intrusive to most intrusive OR from the least expensive to the most expensive to have the most efficent repair process. I have outlined this below, however the most common fix for P0401 is a clogged EGR core.
Engine Air Filter: The cheapest fix for a P0401, Restricted air coming into the engine can cause unexpected air readings and combustion mixtures. Be sure to check to make sure the filter is clean and qaulity to OEM Ford FA-1902.
MAF Sensor: A dirty or damaged MAF sensor can cause unexpected air readings causing incorrect calculations. Try cleaning this sensor especially if you have KN&N filter.
EGR Exhaust Leaks - A leaking pipe going from the exhaust manifold to the EGR valve can cause reduced flow. The exhaust manifold pipe bolts are known to break.
MAP Sensor - Sensor on top of the intake manifold becomes clogged up with carbon. Remove the sensor and lightly tap the carbon out and use a small pick to loosen the carbon.
Clogged EGR cooler - The EGR Cooler accumulates carbon buildup due to the cooler being on the hotside with exhaust gases dead-ending in the cooler when the EGR valve is shut.
Stuck EGR Valve - A sticking EGR valve can cause a P0401 code but usually also results in other EGR Valve position failure codes. Something to be aware of is the chassis cab versions of the Superduty utilize a cast iron EGR valve housing that does tend to warp.
What is the recommended fix for P0401 code on a 6.7L Power Stroke?
The most common cause of the P0401 code in the 6.7L Power Stroke engine is almost always replacing the clogged EGR cooler core. This is due to the restricted flow through the EGR cooler due to carbon buildup. The cooler core can be replaced without replacing the entire housing.