Pulling Codes: P00C6 - Engine Fuel Rail Pressure Low

Pulling Codes: P00C6 – Direct And To The Point

In this month’s Pulling Codes case, Contributing Writer Carlton Banks addresses a direct injection fuel pressure code (P00C6-Fuel Rail Pressure Low during Engine Cranking). The owner of a 2012 Chevrolet Impala states it appears to lose power at times. After the vehicle runs for quite some time, the power issue appears to go away.

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This article will address a direct injection fuel pressure code from another vantage point. The code that we are pointing reference to is P00C6-Fuel Rail Pressure Low during Engine Cranking. I am very aware that this code may not have been encountered by many as of yet. This failure was unique in that it allowed one to witness theory truly coming to life.
The owner of the vehicle states it appears to lose power at times. After the vehicle runs for quite some time, the power issue appears to go away. Our subject vehicle is a 2012 Chevrolet Impala with a 3.6L engine. The first step in our analysis is to verify the customer’s complaint.


Quick System Review

A review of the system’s operation and description can be helpful to provide a better understanding of how it all works. The high fuel pressure necessary for direct injection is supplied by the high pressure fuel pump. The high pressure fuel pump is mounted on the rear of the engine and is driven by a three-lobe cam on the bank 2 exhaust camshaft. This high pressure fuel pump also regulates the fuel pressure using an actuator in the form of an internal solenoid-controlled valve.
In order to keep the engine running efficiently under all operating conditions, the engine control module (ECM) requests pressure ranging from 2 to 15 MPa (290 to 2,176 psi), depending on engine speed and load. Output drivers in the ECM provide the high pressure fuel pump control circuit with a 12V pulse-width modulated (PWM) signal, which regulates fuel pressure by closing and opening the control valve at specific times during pump strokes. This effectively regulates the portion of each pump stroke that is delivered to the fuel rail.
When the control solenoid is not powered, the high pressure fuel pump operates at maximum flow rate. In the event of high pressure fuel pump control failure, the high pressure system is protected by a relief valve in the high pressure fuel pump that prevents the pressure from exceeding 17.5 MPa (2,538 psi).

The fuel rail fuel pressure sensor provides the feedback necessary to the ECM to control the high pressure fuel pump and the fuel injectors. This sensor is diagnosed separately from the fuel pressure control system.

The ECM monitors the fuel rail fuel pressure sensor and the high pressure fuel pump actuator to determine if the commanded and actual pressures are within a predetermined range during engine cranking and at all times while the engine is running. The ECM also monitors the high pressure fuel pump actuator to make sure it is operating within expected limits.

I have provided a series of pictorials showing the activity of the vehicle from a basic startup to traveling down the road at cruise. The scan tool of choice is the Tech 2; Figure 1 shows the code we are addressing, P00C6. I have also provided a series of additional snapshots (Figures 2-6) to give a good understanding of how the fuel system is performing.

Let’s begin by looking at a first start of the day. Figure 2 shows a low side pressure of 46 psi and high side pressure of 585.8 psi.

I then watched as the vehicle started to adjust for idle speed conditions with transmission in park, Figure 3 shows a stable low side pressure of 43 psi and a high side pressure of 391.5 psi at idle.

I then decided to take the vehicle for a cruise down the road, the transmission was placed in Drive and off I went to witness my observation of how the pressure would change under these conditions. The low side pressure was at 42 psi and the high side pressure was at an impressive 606.1 psi.

Then I noticed something that was very strange, the low side pressure increased to 73 psi and the high side was decreased to the point where both sides were almost equal. This implies a high pressure pump that is not working (68.2 psi vs. 70 psi).

It was very interesting to see this activity occur right before my eyes, I then decided to continue to observe to see if the pump would recover. Figure 6 shows a very smooth recovery back to normal pressures. The low side then returned to less than 43 psi.

A test was also run to determine if injectors may be leaking, the system passed the leakdown test. The conclusion draw was to replace the high pressure pump assembly. The high pressure pump was replaced and the vehicle is now operating as designed.

This Pulling Codes case is now closed.

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