Here is an attempt at a summary.
A full explanation of FSI can be found in the
Self-Study Programme, however for this error it is sufficient to know that the intake manifold contains flaps that are either activated or not activated. They are activated by the vacuum actuator which is controlled by the air flow control value (N316) and the position of the flaps is detected by the potentiometer (G336). This setup can be seen in the image below.
The intake cross-section (not shown) is divided into upper and lower ducts. When the flaps are activated, they rise to close off the lower duct and redirect the air into the upper duct otherwise the air flows through both ducts. An animation of the process can be see in
this video. The Table below shows the state of the flaps under different conditions.
Engine State | Flaps State |
Ignition on | Not activated |
Idle | Activated |
RPM < ~3200 | Activated |
RPM > ~3200 | Not activated |
Ignition off | Activated |
Note that the flaps are activated when the ignition is switched off and not activated when the ignition is switched on. A residual vacuum keeps the flaps activated for as long as the vacuum can be maintained. When the Ignition is switched on, the vacuum is purged and the
FSI click is herd when the flaps return to the not activated position under the force from a spring.
The
P1031 error means that the ECU expected the flaps to be either activated or not activated and this did not match the actual position measured by the potentiometer (G336) for at least three times consecutively. The cause could be mechanical, electrical or calibration and best diagnosed with VCDS as this is the only way to do the adaption (calibration). Measuring block 142 shows the actual and expected flap positions as well as the offset voltage and adaption status. It is also useful to display measuring block 01 to obtain the engine RPMs.
The mechanical operation of the flaps can tested by manually applying a vacuum. The vacuum pipe can be disconnected from the control valve (N316), rotated under the air intake and a vacuum created by sucking on the end of the pipe. The travel of the vacuum actuator arm should be approximately ~15mm. Placing small Tipex marks on the vacuum actuator arm can help with observing the range of movement.
The air flow control valve (N316) and vacuum can be checked as the flaps should be activated when the engine is at idle and hence the vacuum actuator arm should move by ~15mm. The control valve has two electrical connections, connection 1 (green/yellow) is 11.6v and connection 2 (purple/yellow) is 11.6v when closed and when open is 0.36v. The resistance between connection 1 and connection 2 should be approximately 30Ω.
If everything seems fine, then either the offset voltage needs to be changed or there is an issue with the potentiometer. The potentiometer has three connections, connection 1 (purple/red) is 5v ± 0.5 , connection 3 (grey/green) is ground and connection 2 (yellow/red) is ~2.6v when the flap is open and ~3.9v when the flap is closed. The resistance between connection 1 and connection 3 should be 1.80 to 2.20 kOhm. When the Basic Setting is run, the ECU will update the offset voltage and hence the voltage for the position of the flaps when they are not activated.
Hope that helps.