Audi Fuel Pressure Diagnosis
This bulletin applies to 2009 Audi A3 models and is applicable to various other Audi models. The MIL may be on, with one or more of the following DTCs stored in the ECM data memory:
P310B (low-pressure fuel system regulation, fuel pressure outside tolerance)
P129F or P008B (low-pressure fuel system, pressure too high)
P129E or P008A (low-pressure fuel system, pressure too low)
P2540 (low-pressure fuel system, pressure out of range)
P0087 (rail fuel pressure system, pressure too low)
Comparing Measure Value Block 103 with 106 is not an accurate method to diagnose low-side fuel pressure sensor G410. In order to diagnose G410 accurately, use a mechanical gauge and compare results with the low-side fuel pressure Actual Value in the applicable Measured Value Block (varies by engine).
1. Verify that the customer did not run out of fuel at the time the DTCs were stored. TIP: P310B and/or P008A may be accompanied by P1250. If so, it is likely the faults occurred due to a low fuel level and not a malfunction of the G410 pressure sensor.
2. Follow indication of GFF for applicable DTCs.
3. To check the low-side fuel pressure sensor G410, measure the fuel pressure with a mechanical gauge using the following method:
a. Start the engine and allow it to idle for at least one minute.
b. Stop the engine.
c. Keep the ignition on.
d. Measure actual low-side fuel pressure with mechanical gauge VAG 1318 on the low pressure supply line in the engine compartment (Figure 1).
4. Add 1 bar to the value obtained from the mechanical gauge to calculate the adjusted gauge measurement value.
5. Compare the adjusted gauge measurement value to the Actual Value stored in the applicable low pressure MVB. In some cases, the MVB actual value is shown in hPa instead of bar. For comparison, 1 bar = 1,000 hPa (5,000 hPa = 5 bar).
6. If the MVB value deviates more than +/- 1.0 bar from the adjusted gauge measurement value, the DTC was likely triggered by a faulty G410 low-side fuel pressure sensor. In this case, document the adjusted gauge measurement value and MVB value on the repair order and replace the G410 low-side fuel pressure sensor. (see Figure 2).
7. Clear DTCs and verify that the problem has been eliminated.
8. If applicable, run Basic Settings to adapt the low-side pressure system.
9. Do not replace the high pressure fuel pump, electrical fuel pump, fuel pump control module or fuel filter unless the problem persists and further diagnosis indicates a malfunction of any of these components.