This DTC trouble code is classified as a generic OBDII trouble code and can be found in many makes and models from 1996 and above. While the methods for tracking down your fuel pressure regulator issues may be the same, the make and model of your specific vehicle may differ.
Today’s DTC Doctor focuses on a 2003 Mercedes Benz S55 5.4L Supercharged AMG with a M113 ML55 engine, and we’ll be servicing the fuel pressure regulator as part of the P0089 DTC OBDII trouble code.
If you have this trouble code, chances are you will need to service your fuel pressure regulator. Regardless of whether or not your vehicle has a returnless fuel system, or a normal fuel system with a return, problems with your FPR can cause your DTC P0089 code.
If your vehicle is a normal return system, chances are the fuel pressure regulator is located on the fuel rail of your engine. If your vehicle is returnless the regulator may reside inside the fuel pump assembly, or the fuel tank itself. Returnless fuel systems are computer controlled and the fuel pump output and actual fuel rail pressure is determined by a fuel pressure sensor on the rail that uses the temperature of the fuel to determine the actual pressure.
When you’ve got an issue with your fuel pressure regulator and your car throws the P0089 trouble code, it may negatively affect how the car runs and operates. As the fuel pressure regulator maintains proper pressure at the fuel rail, premature engine failure can occur if this problem is left alone.
Symptoms of the DTC P0089 can include, but not limited to;
- Poor fuel economy
- Poor acceleration or hesistation
- Engine knock or detonation
Before going out and purchasing a replacement fuel pressure regulator, causes of the DTC P0089 can include, but not be limited to ;
- Fuel pump failure
- Fuel pump lines are restricted or pinched
- clogged fuel filter
- electrical wiring
- bad vacuum connection
To being troubleshooting you should first check the pressure at the rail, after referencing what the pressure should be in working condition. Our M113 ML55 engine does feature a test port for testing fuel pressure, but your vehicle may so please check there before replacing your fuel pressure regulator.
Your fuel pressure can be measured by undoing the cap circled in pink located in the picture above. This port will allow you to connect a Mercedes Benz Fuel fitting part number of 13 0 060 and tee piece 13 3 064 and test the pressure in your rail as pumped by your fuel system.
Using a voltmeter check the voltage from the fuel pump assembly to insure that your pump is receiving a full 12 volts. If there is a lack of power, check the wiring for breaks or excessive resistance in the wiring.
If your vehicle utilizes a returnless fuel system the trigger wire can be checked using a graphing multimeter in order to properly sync the duty cycle. As a general rule of thumb, the duty cycle from the fuel pump computer will be double what the computer commanded duty cycle is commanded by the PCM/ECM.
After checking our fuel pump voltage and making sure that our fuel filter is not the problem, we can commence to the next steps of servicing our fuel pressure regulator. Next check the fuel lines, both hard and soft lines for any kinking or damage that could cause blockage or lack of proper pressure.
Check the fuel pump relay in the engine bay and jump the terminals 87 and 30 with a clip or wire, and check fuel pressure.
The fuel pressure regulator with the fuel pressure damper unit, with the Mercedes part number 1120780092. This unit can be located inside the fuel tank alongside your fuel pump assembly and must be replaced if your issue is not fuel pump related, for our vehicle in question it’s mounted under the fuel rail.
If you are not comfortable working around an open head or not comfortable working on an engine with open ports, stop now and take your vehicle to an experienced ASE certified mechanic. Pro Street Online is not responsible for any damage that may occur from following this guide or writeup.
This regulator is mounted on the underside of your fuel rail between your fuel injectors, to access this unit remove the bolts that secure your fuel rails to your engine and lift slowly.
There is a large circlip that secures the fuel damper to the underside of your fuel rail, undo this clip now and gently remove your damper.
Once you have the damper removed, install the new unit and make sure it’s firmly seated before reinstalling your circlip.
Congratulations! You have now resolved your P0089 Fuel Pressure Regulator issue! Happy Driving!
