|Trouble Code||Fault Location||Probable Cause|
|P0088||Fuel rail/system pressure too high||Fuel pump, fuel pressure regulator, fuel supply pipe blockage, mechanical fault|
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What Does Code P0088 Mean?
OBD fault code P0088 is defined as “Fuel Rail/System Pressure – Too High”, and is set when the PCM (Powertrain Control Module) detects an abnormally high pressure in the fuel rail, or sometimes in other parts of the fuel system.
All fuel injection systems are designed to operate within a predetermined range of pressures to ensure smooth operation of the engine under all operating conditions, and engine speeds/loads. Thus, when the PCM detects a fuel pressure that exceeds predetermined values, a code will be stored, and the CHECK ENGINE light will be illuminated.
However, the range of ideal fuel pressures vary widely between vehicles, so consult the relevant manual to determine the correct range of pressures for the vehicle being worked on.
The cut-away drawing below shows the typical construction of a fuel rail-mounted fuel pressure regulator.
What are the common causes of code P0088?
There are not many causes of excessive fuel pressure. Since the fuel pump is running, it means that the problem usually does not involve electrical issues. Some of the most common causes of high fuel pressure include the following-
- Defective fuel pressure regulator
- Clogged filter screens in the pressure regulator
- Kinked, or damaged fuel return line
Wrongly installed fuel filters (Note that if the fuel filter is installed the wrong way round, which is possible on some applications, there will be a high pressure condition only between the filter and the pump. The pressure between the filter and the rail will be lower than normal (or absent) because the filter might not allow a reverse flow.)
Defective fuel pressure sensor (Note that while a defective sensor could possibly set code P0088) it is more likely to deactivate the pump than to cause a high fuel pressure condition. In practice, it is more common for defective fuel pressure sensors to set low fuel pressure related codes.)
What are the symptoms of code P0088?
In some cases, there may be no symptoms apart from a stored code and an illuminated CHECK ENGINE light. However, depending on the degree of deviation from defined fuel pressures, some, or all of the following symptoms may be present-
- No start condition
- Hard starting condition
- Increased fuel consumption
- Black smoke from the tail pipe may be present
- Rough, erratic or uneven idling
- Loss of power and performance
- Oil dilution in severe cases
- Damaged catalytic converter(s)
- Fouled sparkplugs
NOTE: In severe cases, other codes that relate to emission control faults may be present, especially codes that relate to catalytic converter(s), and oxygen sensors.
How do you troubleshoot code P0088?
NOTE #1: Apart from a repair manual, a dedicated fuel pressure gauge is required to accurately diagnose code P0088. It is a common mistake to replace the fuel pump (and other expensive components) in attempts to remedy a no starting condition. Code P0088 indicates excessive fuel pressure, and the only way to determine the actual pressure is to test the pressure in the system with a proper fuel pressure gauge.
NOTE #2: Many applications use a pressure sensor to continually monitor the pressure in the fuel system. This sensor must not be confused with the pressure regulator, which opens and closes in response to varying pressures to maintain the specified fuel pressure. A defective pressure sensor could conceivably set code P0088 on some applications, which is why it is important to physically check the actual pressure in the system with a pressure gauge.
NOTE #3: If the vehicle is fitted with a fuel pressure sensor, consult the manual on the correct testing procedure. Compare obtained readings against the manufacturer’s pressure-to-Hertz chart, and replace the sensor if readings do not conform to specified values. Defective pressure sensors can deactivate the fuel pump on some applications, so be sure to check the operation of this sensor in conjunction with the actual fuel pressure if the vehicle can start.
Begin the diagnostic procedure by recording all stored fault codes and available freeze frame data. This data can be useful if an intermittent fault is diagnosed later on.
Sine code P0088 indicates an excessive fuel pressure the problem is unlikely to be caused by wiring issues, unless the fuel pressure regulator is electrically operated. In some applications the pressure regulator is located on the fuel rail and operated by a spring with vacuum assistance obtained from the inlet manifold. On other systems/applications, the regulator is located on, or near the fuel pump. Consult the manual to determine the location of the pressure regulator.
NOTE #1: To ensure that the fuel pump is not being fed too high a current, perform reference, resistance, and continuity checks on all associated wiring. Repair all wiring found to be defective. Note that an excessive voltage is a rare occurrence, but perform all relevant tests to ensure that the pump is receiving the correct current, which is usually equal to the battery voltage.
NOTE #2: Also perform a thorough inspection of all fuel lines, in particular the return line that delivers fuel from the fuel rail back to the tank. If this line is restricted due to damage of some kind, the pressure in the system cannot be relieved effectively. Consult the manual to determine the location and routing of all fuel lines, and replace all damaged fuel lines as required. Also be sure to check that the fuel filter is correctly installed.
If the vehicle can start, connect the fuel pressure gauge to the system, but leave the code reader connected. Start the engine, and monitor the actual pressure in the fuel system via the gauge, and the scanner. If the pressure rises steeply, or remains steady whatever the reading, it is almost certain that the pressure regulator is faulty.
NOTE#1: During normal operation, fuel is delivered to the fuel rail under a constant pressure and volume. The fuel pressure regulator is designed to relieve the pressure in the system when demand decreases, so during this test, vary the engine speed to change the demand for fuel. If the pressure remains constant despite varying engine speeds, the pressure regulator is defective.
NOTE#2: If the pressure fluctuates in response to the changing demand, but remains higher than the specified maximum, the pressure regulator is opening only partially, which is the same as being defective.
If the pressure regulator is located on the fuel rail, it is likely to be spring operated, but supplied with vacuum assistance. Replace the vacuum hose if a leak is suspected, and repeat Step 3. If the problem persists and there is a strong vacuum present, replace the fuel pressure regulator and repeat Step 3 after clearing all fault codes.
If the vehicle cannot start, it is most likely because the excessive fuel pressure is deactivating the pump. This is not always easy to determine, so if the vehicle does not start when code P0088 is present, and the pressure regulator is located inside the fuel tank, the best course of action is to remove the pump canister from the tank. Consult the manual on the correct procedure to remove the pump, and to replace the regulator.
NOTE: Also perform continuity/resistance checks on the pump to confirm that the excessive pressure had not damaged the pump motor. Replace the pump if obtained readings do not conform to values stated in the manual. Be sure however to disconnect the pump from the PCM before commencing continuity checks to prevent damaging the controller.
Reassemble the fuel pump and related components, clear all codes, and see if the engine will start. If it does start, check the system pressure to confirm that it falls within the specified range.
NOTE: It goes without saying that it is crucially important to check the fuel system for leaks after fuel lines had been disconnected. Repair all leaks found, and check the system again to ensure there are no more leaks anywhere in the system.
Make sure all codes are cleared, and test drive the vehicle with a suitable scanner connected to record the fuel pressure under changing engine loads/speeds. If the scanner cannot monitor live data streams, retest the fuel pressure after the test drive, and scan the system to see if the code has returned.
In the unlikely event that the code persists, it is possible that there is an intermittent fault present, which may have to be allowed to worsen before an accurate diagnosis and repair can be made. This obviously only applies to vehicles that can still be driven.
Codes Related to P0088
- DTC P0087 Fuel Rail/System Pressure – Too Low
- DTC P0088 Fuel Rail/System Pressure – Too High
- DTC P0089 Fuel Pressure Regulator 1 Performance
- DTC P0090 Fuel Pressure Regulator 1 Control Circuit
- DTC P0091 Fuel Pressure Regulator 1 Control Circuit Low
- DTC P0092 Fuel Pressure Regulator 1 Control Circuit High
- DTC P0093 Fuel System Leak Detected – Large Leak
- DTC P0094 Fuel System Leak Detected – Small Leak