Signal Too Low
Signal too low
Checking the fuel pressure sensor
Note! If diagnostic trouble codes (DTC) for the fuel pressure sensor or atmospheric pressure sensor are stored, these diagnostic trouble codes (DTC) must be fault-traced and remedied first.
Hint: The method below is used to check whether the diagnostic trouble code (DTC) was caused by a faulty fuel pressure sensor. This can be done by comparing the fuel pressure sensor signal (displayed in VIDA) with the actual fuel pressure (displayed on a manometer connected to the wiring for the fuel injection system). This method assumes that the manometer for measuring fuel pressure is correctly calibrated.
- Connect the manometer. See: Fuel pressure gauge Fuel Pressure Gauge
Caution! The pressure in the fuel injection system can reach approximately 650 kPa when this diagnostic trouble code (DTC) is stored. Use an adapted manometer.
- Run the engine to operating temperature. Allow the engine to idle.
- Air conditioning (A/C) off.
Read off the relative fuel pressure.
The relative fuel pressure is calculated from the fuel pressure sensor and the atmospheric pressure sensor signal (= absolute pressure minus atmospheric pressure).
Check that the value on the manometer and the value displayed in VIDA are the same. If the values are different, the circuit for the fuel pressure sensor is defective.
Is the fuel pressure sensor correct?
Yes - Checking regulation of the fuel pressure
No - Checking the component and wiring
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Checking regulation of the fuel pressure
Warning! In this test, the pressure in the fuel injection system will reach approximately 650 kPa. Disconnect the pressure gauge; it is not intended for use at such high pressures.
Hint: The method described below is used to check the control of the pressure in the fuel injection system by activating the quick test for the fuel pump (FP). If the pressure gauge for pressures up to 650 kPa is connected, the fuel pressure sensor can also be checked during this test.
Note! In this test, the complete flow capacity of the system is not tested.
- Disconnect the manometer unless it is adapted for pressures higher than 650 kPa
- Run the engine to operating temperature. Allow the engine to idle.
- air conditioning (A/C) off
- Read off the fuel pressure and the fuel pressure desired value.
- Start the quick test when the engine is running at idling.
During the course of the quick test, the control module regulates the pressure for different target values in different steps (530, 490, 450, 410, 440, 490, 530 kPa). The test usually starts with the pressure momentarily going up to 650 kPa.
Note! Because the by-pass valve in the fuel pump (FP) will be open at approximately 650 kPa, the pressure will not go higher than this.
Hint: The illustration to the left shows an example of normal regulation.
- The upper digital display and the graphic display (red font color) indicate the absolute fuel pressure, calculated from the fuel pressure sensor
- The central digital display and the graphic display (blue font color) indicate the control module target value for the absolute fuel pressure
- The lower digital display indicates the relative fuel pressure (white font color), calculated from the fuel pressure sensor and the atmospheric pressure sensor (= absolute pressure minus atmospheric pressure). If a manometer is connected during the test, it must indicate this pressure.
Check that the value for absolute fuel pressure is the same as the target value for absolute fuel pressure. If the values are not the same, this indicates a fault in the pressure regulation. The values may differ during the quick test when the target value is changed. This is due to sluggishness in the fuel regulation and is normal. In some cases, it can take up to 5 seconds before the fuel pressure reaches the target value for the fuel pressure.
Is the function OK?
Yes - Checking components
No - Checking components
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Checking components
Hint: The fault may be intermittent or be due to the flow capacity in the system being too low.
Check that the fuel level in the tank is not too low (almost no fuel).
Check the fuel lines between the fuel pump (FP) and the fuel rail for the injectors for leakage.
Check the fuel pressure sensor connectors. Check for contact resistance and oxidation.
Check the connector for the fuel pump (FP) control module. Check for contact resistance. Check for oxidation.
Check the fuel lines and fuel filter for blockage.
Remedy as necessary.
Try a new fuel pump (FP) if no fault is found during the above fault-tracing.
Other information
- Connecting the breakout box, B5254T7 Connecting the Breakout Box, Engine Control Module (ECM)
- Signal specification, B5254T7 Signal Specification
- Fuel pump and level sensor unit, B5254T7, AW55-50/51SN, B5254T7, M66 Service and Repair
- Fuel pump driver module, B5254T7 Service and Repair
- Checking wiring and terminals Checking Wiring and Terminals
Continue - Fault-tracing information
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Fault-tracing information
Information
Fault-tracing information
If the fault is intermittent, do not verify fault-tracing if the fault does not recur.
It is possible to view the information again, or leave fault-tracing for this diagnostic trouble code (DTC).
Do you want to view the information again?
Yes - Attempt New Test
No - FAULT FOUND
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Attempt New Test - Checking the fuel pressure sensor
FAULT FOUND - DONE
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Checking the component and wiring
Check the fuel pressure sensor connectors. Check for contact resistance and oxidation.
Remedy as necessary.
Try a new fuel pressure sensor if no fault is found during the above fault-tracing.
Other information
- Connecting the breakout box, B5254T7 Connecting the Breakout Box, Engine Control Module (ECM)
- Signal specification, B5254T7 Signal Specification
- Pressure sensor, fuel rail (FRP), B5254T7 Service and Repair
- Checking wiring and terminals Checking Wiring and Terminals
Continue - Verification
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Checking components
Check that the fuel level in the tank is not too low (almost no fuel).
Check the connectors between the fuel pump (FP) control module and the fuel pump (FP). Check for contact resistance. Check for oxidation.
Check the fuel lines and fuel filter for blockage.
Remedy as necessary.
Try a new fuel pump (FP) if no fault is found during the above fault-tracing.
Hint: The diagnostic trouble code (DTC) can also be caused by a defective fuel pump (FP) control module.
Other information
- Fuel pump and level sensor unit, B5254T7, AW55-50/51SN, B5254T7, M66 Service and Repair
- Fuel pump driver module, B5254T7 Service and Repair
- Checking wiring and terminals Checking Wiring and Terminals
Continue - Verification
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Verification
Verification
Hint: After carrying out the repair, check that the fault has been remedied.
- Connect the manometer. See: Fuel pressure gauge Fuel Pressure Gauge
- Run the engine to operating temperature. Allow the engine to idle.
- Air conditioning (A/C) off.
Read off the relative fuel pressure.
The relative fuel pressure is calculated from the fuel pressure sensor and the atmospheric pressure sensor signal (= absolute pressure minus atmospheric pressure).
Check that the value on the manometer and the value displayed in VIDA are the same. If the values are different, this indicates incorrect function.
Is the function OK?
Yes - VERIFIED
No - VERIFICATION FAILED
------------------------
VERIFIED - FAULT FOUND
VERIFICATION FAILED - Fault-tracing information
-------------------------------------------------
Verification
Verification
Hint: After carrying out the repair, check that the fault has been remedied.
- Run the engine to operating temperature. Allow the engine to idle.
- air conditioning (A/C) off
- Read off the fuel pressure and the fuel pressure desired value.
- Start the quick test when the engine is running at idling.
During the course of the quick test, the control module regulates the pressure for different target values in different steps (530, 490, 450, 410, 440, 490, 530 kPa). Each step takes 10 seconds. The test usually starts with the pressure momentarily going up to 650 kPa.
Note! Because the by-pass valve in the fuel pump (FP) will be open at approximately 650 kPa, the pressure will not go higher than this.
Hint: The illustration to the left shows an example of normal regulation.
- The upper digital display and the graphic display (red font color) indicate the absolute fuel pressure, calculated from the fuel pressure sensor
- The central digital display and the graphic display (blue font color) indicate the control module target value for the absolute fuel pressure
- The lower digital display indicates the relative fuel pressure (white font color), calculated from the fuel pressure sensor and the atmospheric pressure sensor (= absolute pressure minus atmospheric pressure). If a manometer is connected during the test, it must indicate this pressure.
Check that the value for absolute fuel pressure is the same as the target value for absolute fuel pressure. If the values are not the same, this indicates a fault in the pressure regulation. The values may differ during the quick test when the target value is changed. This is due to sluggishness in the fuel regulation and is normal. In some cases, it can take up to 5 seconds before the fuel pressure reaches the target value for the fuel pressure.
Is the function OK?
Yes - VERIFIED
No - VERIFICATION FAILED
------------------------
VERIFIED - FAULT FOUND
VERIFICATION FAILED - Fault-tracing information
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Fault-tracing information
Attempt New Test - Checking the fuel pressure sensor
FAULT-TRACING FAILED - No Fault Found
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