Testing exhaust gas recirculation: Audi 1.9 TDI (1Z, AHU)

AHU
The function of the exhaust gas recirculation system is tested by checking the mass of air inducted. If exhaust gas is being recirculated, a smaller quantity of fresh air is registered by the air mass meter. The more exhaust gas recirculated, the weaker the signal from the air mass meter.

Special tools and workshop equipment required

VAS 5051 with VAS 5051/1 and VAS 5051/2

or

V.A.G 1551 with V.A.G 1551/1

Test requirement:

Coolant temperature at least 80 °C

Test sequence

Read measured value block, Display Group 001:

=> Diesel direct injection and glow plug system (TDI 4-cyl.); Repair group 01; Reading measured value block
Diesel direct injection and glow plug system (TDI 4-cyl.)
Reading measured value block

Read measured value block 1
⇒
840 rpm
6.5 mg/H
1.480 V
87.3 5C
Indicated on display:

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

Wait until the coolant has reached the specified temperature before continuing with the test.
Read measured value block, Display Group 003.

Read measured value block 3
"
840 rpm
272 mg/H
268 mg/H
54 %
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 (spec.) · 3 (actual)
230...370 mg/H · 230...370 mg/H · Okay
> 370 mg/H · > 370 mg/H · Engine too cold / Electrical equipment on / Temperature of intake manifold too high / Injection pump too lean
230...370 mg/H · < 230 mg/H · Unmetered air / Too much EGR
230...370 mg/H · > 370 mg/H · Too little EGR / or none at all
Constant / 425 mg/H · Fixed substitute value caused by open circuit in wiring to air mass meter or implausible air mass signal

Note:

If display zone 3 shows a constant value of 425 mg/H, check the air mass meter:

=> Diesel direct injection and glow plug system (TDI 4-cyl.); Repair group 23; Testing exhaust gas recirculation; Testing air mass meter -G70
Diesel direct injection and glow plug system (TDI 4-cyl.)
Testing exhaust gas recirculation
Testing air mass meter -G70

If the specifications are not obtained:

Start final control diagnosis and activate exhaust gas recirculation valve -N18:

=> Diesel direct injection and glow plug system (TDI 4-cyl.); Repair group 01; Final control diagnosis
Diesel direct injection and glow plug system (TDI 4-cyl.)
Final control diagnosis

Final control diagnosis
⇒
Exhaust gas recirculation valve -N18
Indicated on display:

The valve must click.

Valve does not click:

Test exhaust gas recirculation valve -N18 => Page 26-29.

If the valve clicks:

Check vacuum hose connections => Page 26-23.

If vacuum hose connections are OK:

Check mechanical exhaust gas recirculation valve
=> Page 26-24.