6.7L Power Stroke P207F DEF Quality Performance Diagnostics
One of the most common issues that people need help with on the 6.7L Power Stroke diesel engine is diagnosing a code P207F. This is one of the harder codes that a 6.7L PSD can throw at you because this code doesn't actually point to a specific problem. This is what is known as a conditional diagnostic trouble code (DTC).
P207F Reductant Quality 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 when a hard fault is actually detected, as such with a Hard Fault DTC.
In the case of the P207F, this code is informing you that your SCR system is not operating correctly. The actual definition of the code P207F is "Reductant Quality Performance". Its such a generalized code that literally means the SCR system is not reducing NoX output effectively and could be because of the quality of the reductant. FYI: Reductant is the diesel exhaust fluid or DEF your exhaust uses to convert NOx.
Because the P207F 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 Selective Catalyst Reduction (SCR) for Performance and DEF Injection Qauntity
The 6.7L Power Stroke PCM monitors the conditions in the exhaust system by using 4 EGT sensors, 2 NoX sensors, a DPFE sensor for the particulate filter, and a particulate matter sensor. All these sensors work together so that the PCM can monitor and control emissions output. The aim is reducing an emission called NOx or Nitrogen Oxides. These emissions get produced under high cylinder temperatures, which happen often during higher load in a turbocharged engine. So anytime the engine is running and the exhaust is at the proper temperature, the system injects DEF fluid to chemically react with the NOx present in the exhaust.
On the 6.7L Power Stroke, the powertrain control module controls how much DEF is injected, so the harder the engine is working means the more DEF gets injected to counteract the higher concentrations of NOx. Other diesel engines setups (such as some tractors) just inject a set amount of DEF at all times.
The PCM uses information from the front NOx sensor to determine how much DEF to inject, and it monitors information from the rear NOx sensor to determine how effective the system was. The P207F will set if no other codes DEF injection codes are present but the system still is not performing as expected. Expected results would be a significant reduction from NOx ppm at the rear NOx sensor.
P207F Symptoms - Reduced Power, Forced Limited Idle, or Vehicle Speed Limited to 50MPH
If you have a P207F DTC, you may also get a message about Forced Limited Idle Only or Vehicle Speed Limited to 50MPH. This is done to reduce the NOx output of the engine by seriously handicapping the available power output to reduce cylinder temperatures.
Now that you know what is going on, you can start to try to determine the cause of the code. So many things can cause this P207F to set. When performing diagnostics you always start at least intrusive or expensive solution and work toward the most intrusive or expensive possible solution. I am going to lay out, in order, things you should be checking. Some of these do require scan tool access to be effective.
What causes P207F 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.
Engine Air Filter: The cheapest fix for a P207F, 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.
Exhaust Leaks - Any leak in the exhaust can cause the NOx readings to be inconsistent. Leak in the exhaust before the turbocharger can also cause boost related concerns.
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.
EGR Valve - Clogged EGR coolers likely wont lead to P207F, however a sticking open EGR valve can. Use a scan tool to verify EGR_A_POS is less than 1v or at 0% when EGR_A_CMD is 0%.
DEF Fluid - DEF fluid has a expiration date and shelf life, it could be contaminated with other fluids, or even diluted with water. You can use a OTC 5025 Diesel Exhaust Fluid (DEF) Refractometer to check.
NOx Sensor - These sensors age and become biased. While driving the truck you should monitor both NOx1 and NOx2. Simply put, NOx2 should remain less than NOx1. They both should warm up and respond in a timely manner. Sometimes the solution is to install a new NOx2 sensor.
Exhaust System Failure - A clogged particulate filter can cause issues however you generally get other codes confirming this. The SCR mixer or catalyst system could be damaged but this is a last resort because it is so expensive to replace.