Testing exhaust gas recirculation > 06.97: Audi 1.9 TDI (1Z, AFF, AFN, AHH, …)

AFF AFN AHH AHU AVG
The operation of the exhaust gas recirculation system is tested by measuring the intake air mass. If exhaust gas is being recirculated the proportion of fresh air detected by air mass meter will be smaller. The larger the quantity of recirculated exhaust gas, the weaker the signal from the air mass meter.

Special tools, testers and auxiliary equipment required

VAS 5051

or

V.A.G 1551 with V.A.G 1551/3 A

Test requirements:

Coolant temperature at least 80 °C.

Test sequence

Read measured value block, display group 001:

=> Diesel direct-injection and glow lamp system (4-cyl.) ä 06.97; Repair group 01; Self diagnosis of diesel direct-injection system; Reading measured value block
Diesel direct-injection and glow lamp system (4-cyl.) ä 06.97
Self diagnosis of diesel direct-injection system
Reading measured value block

Read measured value block 1
⇒
840 rpm
6.5 mg/stroke
1.480 V
87.3 5C
When adjacent display appears:

Check display in display zone 4 (coolant temperature).
Specified value: at least 80 °C

Do not continue with the test until the coolant has reached the specified temperature.
Read measured value block, display group 003.

Read measured value block 3
⇒
840 rpm
272 mg/stroke
268 mg/stroke
54 %
When indicated on display

Briefly depress the accelerator pedal, then allow the engine to continue running at idling speed.

Observe displays in display zones 2 and 3

Display zone · Possible cause of fault
2 (specified) · 3 (actual)
230...0.370 mg/stroke · 230...0.370 mg/stroke · OK
230...370 mg/stroke · Greater than / 370 mg/stroke · Engine too cold / Load switched on / Manifold temperature too high / Injection pump too lean
230...0.370 mg/stroke · Less than / 230 mg/stroke · Unmetered air / Excessive exhaust gas recirculation
230...0.370 mg/stroke · Greater than / 370 mg/stroke · not enough or no exhaust gas recirculation
230...370 mg/stroke · (constant / 425 mg/stroke · Fixed substitute value, due to break in cable to air mass meter or measurement of implausible air mass

Note:

If display zone 3 shows a constant reading of 425 mg/stroke, test air mass meter:

=> Diesel direct injection and glow plug system (4 cyl.) ä 06.97; Repair group 23; Servicing diesel direct-injection system; Testing air mass meter
Diesel direct injection and glow plug system (4 cyl.) ä 06.97
Servicing diesel direct-injection system
Testing air mass meter

If the specified values are not obtained:

Start final control diagnosis and actuate EGR valve -N18:

=> Diesel direct-injection and glow lamp system (4-cyl.) ä 06.97; Repair group 01; Self diagnosis of diesel direct-injection system; Final control diagnosis
Diesel direct-injection and glow lamp system (4-cyl.) ä 06.97
Self diagnosis of diesel direct-injection system
Final control diagnosis

Final control diagnosis
⇒
EGR valve -N18
Display:

The injector valve should click.

If the injector does not click:

Check EGR valve -N18 => Page
26-43

If the injector clicks:

Check vacuum hoses => Page
26-32
.

If vacuum hoses are OK:

Test mechanical exhaust gas recirculation valve => Page
26-34
.