Technical Description of OBD-II Trouble Code
Intermittent Circuit Issue in the Low Pressure Fuel System Sensor
What does that signify?
This generic powertrain/engine diagnostic trouble code can typically apply to all OBDII equipped engines, but is more commonly found in certain Audi, Ford, and VW vehicles.
The Fuel Pressure Sensor (FPS) is usually located directly mounted into the fuel rail, near the injectors and the intake manifold. The FPS converts the system fuel pressure into an electrical signal for the Powertrain Control Module (PCM).
The PCM receives this voltage signal and possibly one more; Fuel Temperature Sensor (FTS) which may or may not be part of the FPS. The PCM analyzes the FPS sensor voltage to determine the precise amount of fuel to inject into the engine. This code is triggered if this input does not match the normal engine operating conditions stored in the PCM’s memory, even for a brief moment, as demonstrated by this diagnostic trouble code. It also examines the voltage signal from the FPS sensor to determine if it is correct at initial Key On.
This code could have been triggered due to mechanical (typically fuel pressure/volume) or electrical (fuel pressure sensor circuit) issues. These should not be overlooked during the troubleshooting stage, especially when dealing with an intermittent problem.
Troubleshooting steps may vary depending on the manufacturer, type of FPS/FTS sensor, and wire colors.
Symptoms
Symptoms of a P2543 engine code may include:
Causes
Potential causes for this code to be triggered are:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix provided by the manufacturer, which can save you time and money during diagnosis.
Next, locate the FPS sensor on your specific vehicle. This sensor is usually found directly screwed/mounted into the fuel rail, near the injectors and the intake manifold. Once located, visually inspect the connector and wiring. Look for scraping, rubbing, bare wires, burn spots, or melted plastic. Pull the connector apart and carefully examine the terminals (the metal parts) inside the connector. Check if they appear burned or have a green tint indicating corrosion. If cleaning of the terminals is necessary, use electrical contact cleaner and a plastic bristle brush. Allow them to dry and apply electrical grease where the terminals make contact.
If you have a scan tool, clear the diagnostic trouble codes from memory and see if the P2543 code returns. If it does not, then the connections were most likely the problem.
If the P2543 code does return, ensure that you have good fuel pressure by testing with a mechanical gauge. Refer to the manufacturer’s specifications for your vehicle. If the fuel pressure and volume do not meet the requirements, replace the fuel pump, clear the codes, and retest. If the P2543 code is now gone, then the issue was mechanical.
If the P2543 code does return, we will need to test the FPS sensor and its associated circuits. With the Key Off, disconnect the electrical connector at the FP sensor. Connect a Digital Voltmeter black lead to the ground terminal at the FP sensor wiring harness connector. Connect the red lead of the Digital Voltmeter to the power terminal at the FP sensor wiring harness connector. Turn Key On Engine Off. Check the manufacturer’s specifications; the voltmeter should read either 12 volts or 5 volts. If not, repair any open wiring on the power or ground wire, or replace the PCM.
If the prior test passed, we will need to test the signal wire. With the connector still disconnected, move the red lead of the voltmeter from the power wire terminal to the signal wire terminal. The voltmeter should now read 5 volts. If not, repair any open wiring on the signal wire, or replace the PCM.
If all prior tests have passed and you continue to get a P2543, this would most likely indicate a failed FPS sensor, although a failed PCM cannot be ruled out until the FPS sensor has been replaced. If unsure, seek assistance from a trained automotive diagnostician. PCMs must be programmed or calibrated to the vehicle in order to be installed correctly.
