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Testing exhaust gas recirculation valve > < Testing exhaust gas recirculation

A4 Mk1

#Diesel direct injection and glow #plug system (4-cyl.)>06.97
Testing exhaust gas recirculation
Testing operation

The exhaust gas recirculation function is tested by way of the intake air mass. If exhaust gas is being recirculated, the proportion of fresh air sensed by the air mass meter is smaller. The greater the volume of exhaust gas recirculation, the lower the signal from the air mass meter.
 
→ Read measured value block (function 08) and select display group 01, engine idling
=> Page
Read measured value block 1     ⇒
    840 rpm    6.5 mg/S    1.480 V    87.3 oC
  • ‒ Observe reading in display field 4 (coolant temperature).
 
→ Desired value: at least 80 oC.
Read measured value block 1     ⇒
    840 rpm    6.5 mg/S    1.480 V    87.3 oC

Do not continue with test until coolant temperature has been attained.

  • ‒ Press button C and enter 03 for "Display group 03".
 
→ Display:
Read measured value block 3     ⇒
    840 rpm    272 mg/S    268 mg/S    54 %
  • ‒ Give short burst of throttle, then allow engine to return to idle.
  • ‒ Observe readings in display fields 2 and 3.
 
→ Display:
Read measured value block 3     ⇒
    840 rpm    272 mg/S    268 mg/S    54 %

Display field 2
(desired)

Display field 3
(actual)

Possible cause

230...370 mg/S

230...370 mg/S

OK

Greater than 370 mg/S

Greater than 370 mg/S

Engine too cold
Load switched on
Injection pump too lean

230...370 mg/S

Less than 230 mg/S

Leakage air
Excessive exhaust gas recirculation

230...370 mg/S

Greater than 370 mg/S

not enough or no exhaust gas recirculation

Constant 425 mg/S

Fixed substitute value because:
Break in cable to air mass meter or measurement of implausible air mass
 
→ If desired values are not attained, perform final control diagnosis and actuate EGR valve -N18 => Page .
Final control diagnosis    ⇒
EGR valve -N18

EGR valve must click when actuated.

  • ‒ If valve does not click, test EGR valve -N18 .
  • ‒ If valve clicks, check vacuum hoses => Page 23-73.
  • ‒ If vacuum hoses are OK, test mechanical EGR valve

=> Engine mechanical system; Repair Group 26

Testing exhaust gas recirculation valve > < Testing exhaust gas recirculation