The Four Year MIL Case Study - 2011 Ford F250 - Intake Air Measurement
A high mileage but well cared for F-250 came in with a complaint of low power. The technician noticed that the MIL was on and asked the customer how long it had been on. The customer stated that it had been on for four years, although the loss of power was gradual and more recent. The IDS capture below shows four codes, with three of them also setting as Pending codes, meaning they failed recently (during the last trip).
Our favorite 6.7L breathing codes are P2073 and P2074, because they usually set for a clogged, missing, or sucked-in air filter. P1247 sets for low boost pressure, and P1548 sets for an air filter restriction. There’s no air filter restriction sensor, so the P1548 sets using similar logic to the P2073 and P2074, and is based primarily on the MAF sensor.
Based on experience and this combination of codes, the technician first checked the air filter. It looked clean, but was an aftermarket (K&N) filter and housing. This appeared to be the only modification on the vehicle, and seemed to be properly mounted and in good shape.
There are a number of good tests later for low boost, and a long list of possible causes could be built for this combination of codes. The technician could have spent hours verifying VGT and wastegate operation, checked for exhaust restrictions, and smoked the intake and ducting for leaks. However, it’s a lot easier to just ask the customer when the K&N filter was installed. “Four years ago.” The MIL has been on since the aftermarket filter was installed. Huh.
Anyone for a MAF Reset?
Given that the low boost has been progressive and more recent, it’s unlikely that resetting the MAF will fix the low boost codes. However, it’s silly to continue diagnosing the drivability complaint when it’s already clear that there are unresolved breathing codes. The capture below shows the reset function being performed using the IDS Scan Tool.
The truck was taken on a test drive after the MAF Reset (and codes were cleared). Surprisingly, not only did none of the codes reset, but the power was restored as well! Hours of testing were avoided. The Scan Tool revealed that only permanent codes remain.
These codes will clear themselves over time, so they really mean “hasn’t passed or failed yet.” In the end, there was nothing wrong with the K&N filter, the installation, the MAF or MAP sensors or the throttle plate, and there were no leaks or restrictions. In fact, the flow chart would never have repaired this vehicle. Only an understanding of the sensitive nature of the PCM’s MAF expectations could result in a fix. Any change in the intake system requires a MAF Reset, even if there was nothing wrong before or after the change.
Nice one Tim, and yes...MAF calibrations can directly affect boost issues.
Hello Tim thanks for the write up. I have a question about the MAF reset. Since this is a diesel, the IDS can't reset fuel trim because we don't have it. So would I be wrong if I assumed that the MAF reset has to do more with the software reaction to the sensor output? Like a crank sensor relearn. General idea is replacing the component warrants a reset of look up tables within the program, or
Hi Joe. That's about right. The 6.7L Powerstroke is very sensitive to MAF readings, but the expected value is a very complicated model that is hard for us to understand. Gasoline engines are air-controlled, so MAF is a very predictable value at idle and we can use it in VE calculations. Diesels are fuel-driven, and MAF isn't really even needed for fuel control - it's primarily for boost, EGR and
Wow, that was very helpful Tim. Thank you for taking the time and offer offering help. I very much appreciate your write up.
Thanks. We appreciate the partnership. If you didn't come to the classes, we couldn't afford to figure out how this stuff really works!
It doesn't apply to your 2011, but look what just came out today: Sep … F-Super Duty - 6.7L - Illuminated Malfunction Indicator Lamp (MIL) - Diagnostic Trouble Code (DTC) P2074 - MAF Sensor Testing Some … F-Super Duty vehicles equipped with a 6.7L engine may exhibit anilluminated MIL with only DTC P2074 stored in the powertrain control module (PCM). Do not