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What causes the rail pressure controller's positive deviation to exceed the upper limit?

2 Answers

Monica

09/02/25 2:18am

Rail pressure controller's positive deviation exceeding the upper limit may be caused by pump oil pressure, nozzle leakage blockage, rail pressure sensor failure, etc. It is recommended that the owner promptly go to a repair station for inspection and take corresponding solutions to avoid affecting vehicle use. Rail pressure positive deviation is one of the common faults in electronically controlled high-pressure common rail systems. In addition, there are rail pressure negative deviation, rail pressure too low, and rail pressure too high. The rail pressure deviation equals the set rail pressure minus the actual rail pressure. If the resulting value is positive, it is a positive deviation; if negative, it is a negative deviation. A positive deviation means the actual rail pressure is low, while a negative deviation means the actual rail pressure is high. Rail pressure too high has a relatively small fault range, and possible causes for such issues are excessive oil intake or poor oil return.

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CamillaFitz

09/14/25 4:41am

I last encountered this situation with my old diesel car during a long-distance trip when the engine suddenly triggered a warning. Upon inspection, it turned out that the metering valve of the high-pressure fuel pump was stuck, causing abnormal fuel injection volume to increase, which naturally led to a surge in rail pressure. Another possibility is that the fuel pressure sensor reported false data, misleading the control unit about the injection volume. Additionally, it's important to check the low-pressure fuel circuit; if the fuel filter is clogged, leading to insufficient fuel supply, this kind of failure can also occur. The most troublesome issue is when the ECU control program malfunctions, which requires connecting a diagnostic tool to accurately read the fault codes. I suggest not pushing through; it's safer to stop the vehicle immediately, turn off the engine, and check the fault codes. Otherwise, if the high-pressure fuel rail really bursts, it would be extremely dangerous.

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