Code Leads Technician Astray
I recently took a hotline call on a 2008 Ford F-250 with a 6.4l diesel engine that had no power and was setting a code P2563. This code, by definition, is related to the turbocharger actuator that controls the variable turbocharger.
The technician told me the vehicle ran fine in that it had no misfire problems and no abnormal exhaust smoke; it just had no power and no turbo boost. The dual turbocharger assembly and the turbocharger actuator had been replaced before the technician called. The original turbo was internally damaged, so there was no way to know how long the vehicle had been having problems.
The technician had verified that after the code was cleared, it would return. Since code P2563 points to a problem with the turbocharger actuator, we started discussing that. The actuator moved as it should when turning the key to "on" and the linkage was connected, which ruled out some of the basics. If the actuator hadn't moved, I would have asked the technician to make sure nothing was mechanically binding within the new turbo, and to check the power and ground to the actuator.
At this point, I had the technician clear the code again and perform the "key on, engine off" self-test. The code did not return. This made me curious. If the actuator worked when commanded and did not set any hard fault codes, then that would prove that there was no problem with the communication wires from the actuator to the powertrain control module (PCM).
Sometimes the PCM uses other sensor inputs to set trouble codes (and in many cases, including this one, the pinpoint test never leads the technician to look at any other inputs), so I suggested that the technician start by dropping the diesel particulate filter (DPF). One of the symptoms of a restricted filter is a severe lack of power.
I also suggested that if the DPF was not plugged, the technician check the exhaust gas recirculation (EGR) valve position voltage to make sure the EGR was not mechanically stuck open. I talked to him several weeks later and found that, in fact, the DPF had been plugged solid. After replacing the DPF, the code was gone and the vehicle's power and performance returned to normal.
The moral of this story: Sometimes we need to diagnose the symptom. We can't always rely on a trouble code and/or a flow chart to lead us in the correct direction!
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