This time about the very popular error message 2AAF. 

This error message corresponds to the low pressure (LP) fuel system and means: to maintain the required pressure in the system (typically – 5 bar), too high or too low electrical voltage should be supplied to the pump. 

Basic information on how the N43/N53 series engine’s fuel system is made, read here.

How the LPFP is managed and how the low-pressure pump management maps are created, read here and here.

So, the basics:

a. the low-pressure pump is placed in the fuel tank, on the right side (from which the fuel is refilled);

b. low-pressure pump is managed via an EKP module, which regulates voltage, supplied to the pump (accordingly, power/energy), receiving information regarding pressure in the contour from the pressure sensor, which is located near HPFP;

c. fuel circulates from the low-pressure pump to the HP pump and the fuel filter, after filter – back to the fuel pump compartment.

This time regarding a problem situation. If the error message 2AAF is recorded, we start the inspection of the problem with the DME freeze-frame:

What conclusions can we draw from this freeze-frame (very typical data):

a. EKP has managed to maintain the required pressure (the actual pressure has been around 5 bar);

b. power supply for the EKP module (clamp No.87) is correct;

c. fuel consumption – adequate (in the same case – relatively low).

Unfortunately, these data don’t contain essential basic information regarding voltage supplied to the pump and current, measured by EKP via load (pump). These data should be looked at in the menu of the EKP module. 

Open the EKP module, and choose analog/live data. Here is an example of how the correct data of the LP pump is idle looks:


a. power supply voltage (clamps No.30/15) is correct. These voltages should be comparable to power supply voltages measured in other modules. The problem of the power supply is not the most common defect, but – if you notice significantly lowered power supply voltage, check the wires, connectors for damages;

b. voltage, supplied to the pump around 6.2 V (Volts). 6 .. 7 V is the correct voltage (in idle);

c. current, which flows through the load (pump), is around 8.4 A (Amperes) 8 .. 9 A is a correct current in idle.

So, in idle (in the current menu), 6.2*8.4 = 52 W (Wats) of electrical power are supplied to the pump. Remember this value! The electrical value is the critical parameter that characterizes the “health” of the whole low-pressure system. 

In this image – the problematic case: 

In this menu, you can see:

a. voltage of the clamp No.30 is 14.40 V – correct;

b. PWM is 85.3%; accordingly, the theoretical voltage in the output is 14.40*0.853 = 12.28 V

c. actual voltage, measured by EKP itself in the output, is 11.60 V, which is 0.60 V lower than the theoretical. Conclusion – EKP works correctly (its output/power switch is not damaged); a 0.60 V drop of the voltage is adequate (such voltage drops in EKP power switch, output LC filter; connections);

d. voltage in the output: 11.60 V; current on load: 9.0 A, electrical power supplied to the pump is 11.60*9.0 = 104.4 W.

Here we see a severe problem: to maintain the pressure of 5 bar, this time to the pump, two times higher electrical power is supplied (104 W vs 52 W) as it usually would be needed! Around 50 W of the electrical power is “lost” somewhere. This “extra” power can be “lost”

a. in the heat (pump, its plain bearings – rubbing, when a damaged winding) or

b. in the mechanical energy (somewhere a second, unplanned fuel “fountain”. 

Note: before these calculations, please, check if EKP stabilizes the pressure of LP contour – make sure it’s not working on emergency mode. In such mode, the LP pump is “doing its best” for you successfully reach the nearest service center. If DME detects that the LP contour is damaged (it cannot reach/maintain 5 bar pressure), it can give the command to EKP to work with PWM close to 100%. 

For the existing (this is a typical/widespread problem in the case of 2AAF) situation, two scenarios are possible:

a. problems with the readings of LP sensor;

b. problems of the pump itself. In this case, the pump receives increased electrical power, but the mechanical strength of the pump is (relatively) reduced. Possible causes – increased rub in the plain bearing, partially damaged electrical winding/collector;

c. the pump maintains correct (in these conditions – 2X increased) mechanical energy, but there are increased losses in the fuel contour, for example, leakages in the connections, rupture of pipelines, etc.

A little more in detail regarding each possible scenario.

Defect of the LP pressure sensor

Possible situation – LP sensor indicates lowered pressure. Here you have to do tests:

a. increase the PWM in the EKP module and check the pressure of the LP contour in DME ../F5/F2/F6. If LP contour pressure rises by increased PWM, it is clear that the sensor can measure more significant pressure. If the PWM in the EKP module is increased, the power via the pump rises, but LP pressure (pictured in INPA) does not increase – this is a very suspicious symptom;

b. check the pressure of the LP contour using manometer. If the manometer and DME INPA data indicate comparable data, it is clear that the problem is precisely in the LP contour. 

Problems with the pump

If the pump works untypically loud, if the sound of the pump is uneven, “shivering” – these are very suspicious symptoms.

Contour problems

Perform a visual inspection of all pipelines and their connections located in the fuel tank. Activate the LP pump and observe if there are any leakages from the contour. 

If the pressure is correct, the LP contour is airtight – the pump is the culprit. “Regular” DC electrical motors are used ar LP pumps – their collectors; brushes are wearing out, the plain bearings are wearing out. These elements have a limited life cycle. 

Quite often, I hear – yes, I see the 2AAF error in the DME error message memory, but the LP pressure is as if correct (around 5bar), and the engine works very correctly – I have no reason to worry. Here we have to understand – to reach this pressure of 5 bar, EKP needs to have an extra “effort”. This is a very suspicious symptom – the LP pump can “die” at any moment, and you will have to bring your car to the service with a car evacuator. I suggest solving the problem before the evacuator should be called. 

Second important nuance – use only high-quality (OEM) pumps! It is not worth saving some tens of EUR and installing short-lift and unreliable fuel pumps.