How to deal with pressure limiting valve failure？

Common rail pressure limiting valve opening failure is one of the most common failures in diesel vehicles. Once the common rail pressure control valve opening failure occurs, the engine will enter the limp function. The engine limits the torque. I hope to help you learn more about the common rail pressure limiting valve failures and solution.

When the pressure in the fuel rail exceeds the set value, the pressure limiting valve will open to limit the pressure. The limp function can ensure that the fuel rail maintains a certain pressure after the fuel rail pressure limiter valve is opened. In this way, even if the vehicle has some failures, the driver can still smoothly drive the vehicle to the nearest repair shop for repair.

Various reasons for the opening of the common rail pressure limiting valve

The oil return pipe has excessive resistance, bends or is blocked.

The rail pressure sensor is damaged.

Damaged fuel metering unit: stuck, coil open, short circuit.

The fuel metering unit circuit or connector is faulty: the wiring harness is open, short-circuited, and the connector is in poor contact.

Occasional power failure of ECU: battery power cord and ground wire are in poor contact, ECU power cord and ground wire are in poor contact.

The injector is stuck.

The pressure relief valve spring is fatigued or the replacement model is incorrect.

The crankshaft sensor is out of alignment.

ECU failure.

The oil supply of the low pressure oil circuit is not smooth.

How to deal with failure

First, check the diesel oil inlet and return lines to make sure there are no problems. The oil inlet pipe from the diesel tank to the engine, and the oil return pipe from the engine back to the diesel tank are free of blockage and no discount. Troubleshoot based on the reason why the common rail pressure limiting valve is open.

Secondly, check the urea pump wiring harness connector at the urea pump end, etc., for water or short circuit.

If the pressure limiting valve is opened too much, most of it will cause the rail pressure to fail to go up during the vehicle driving. By combining the data stream, when we find that if the rail pressure rises slowly and the maximum rail pressure is low, then first It is necessary to find the cause of abnormal vehicle rail pressure, such as whether the fuel tank vent, coarse filter, and fine filter block common rail pipe leakage, pressure limiting valve stuck, high pressure oil pipe or conduit leakage, overflow valve, etc. to gradually solve the problem.

Troubleshooting steps

Read the fault code and make sure that there are two fault codes reported: "Pressure limiting valve opening times exceeded" and "Pressure limiting valve opening time exceeded."

Try to replace the common rail pipe or pressure limiting valve after the failure occurs, because the failure to report means that the common rail pipe has reached the mechanical service life.

Clear reset step.

First of all, we must determine whether the "rail pressure relief valve open" failure of the faulty car is accidental or always exists. If it is accidental, we must follow the car to collect the data at the time of the failure, and focus on the actual rail pressure and theoretical rail when collecting data. Changes in rail pressure. If the actual rail pressure momentarily is much larger than the theoretical rail pressure moment when the vehicle is under heavy load, then the most likely cause of this failure is poor oil return. If the reason is poor oil return, this fault usually occurs when the engine is working at a high throttle.

Judge whether the rail pressure sensor is normal. If an abnormality is found during the inspection, check the condition of the relevant circuit or replace the sensor. Quickly judge the sensor failure, you can use the universal sensor, a tool has 11 purposes, and the auto repair shop is a must-have car repair artifact.

Check whether the fuel metering valve is normal and whether the resistance value of the fuel metering valve is within the normal range of 2.6~3.15Ω. If it is within the range, please check whether the driving voltage of the fuel metering valve has a normal working voltage. In addition, if there is a power failure in the ignition signal line during the engine operation, the metering valve current will be instantaneously 0, so that the oil pump supplies oil with the maximum amount of oil to make the rail pressure instantaneously super high, causing the pressure relief valve to burst open. Therefore, you can follow the car to monitor whether there is a power failure in the ignition signal line.

Monitor engine operating parameters to determine whether the injector is working normally; the criterion is: when the engine is idling, the normal range of the rail pressure control integral is between -2000~+2000mm/s, beyond this range is generally an injector failure Or the injector pipe assembly problem. If the injector is not working well or is blocked, it will also cause the rail pressure relief valve to open failure of the engine under heavy load.