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Checking lambda probe heating > < Engine running problems after cold start

A4 Mk1

Motronic Injection and Ignition System (4 cyl.)
Checking lambda control
Checking function
  • ‒ Read measured value block (function 08) and select Display group 03 =>Page 01-49.
 
→ Display:
Read measured value block    3     ⇒
1    2    3    4

Do not proceed with the test until the coolant temperature shown in Display zone 3 has reached at least 80 oC.

  • ‒ Press the C key
  • ‒ Press keys 0 and 7 (Display group 7 is selected with 07) and confirm entry with the Q key.
 
→ Display:
Read measured value block    7     ⇒
1    2    3    4

Display zone 2 will show the voltage of the lambda probe signal.

  • ‒ If the probe voltage fluctuates very slowly, test the probe heating =>Page 24-46.
  • ‒ If a constant probe voltage of 0.45...0.50 V is displayed then there is an open circuit in the signal wire - check the wiring =>Page 24-50.
  • ‒ If a constant voltage of -0.1...+0.3 V is displayed (mixture too lean), then the mixture control has reached the control stop in the "rich" direction, but the lambda probe still detects "Mixture too lean" =>Fault table, Page 01-11.
  • ‒ If a constant voltage of 0.7...1.1 V is displayed (mixture too rich), then the mixture control has reached the control stop in the "lean" direction, but the lambda probe still detects "Mixture too rich" =>Fault table, Page 01-11.
  • ‒ Press the C key
 
→ Display:
Read measured value block    10     Q
Enter Display group number XXX
  • ‒ If the lambda probe is working properly, select Display group 08 and check the lambda learned values.
 
→ Display:
Read measured value block    8     ⇒
    2ms    -0.7 %    -0.5 %        TB active

The mixture adaptation system has learning ability, i.e. the lambda control can recognise differences between various engines (injector nozzle delivery, compression, fuel pressure etc.) and compensates by adjusting the pre programmed basic injection periods in the map in the control unit. The injection periods are extended or reduced until a mixture ofλ= 1 is achieved. The deviation of the actual injection period from the basic injection period programmed in the map is given as a percentage.

  • ◆ Positive learned value (+...%): Programmed basic injection period too short, actual injection period longer by ...% to achieve λ= 1.
  • ◆ Negative learned value (-...%) Programmed basic injection period too long, actual injection period shorter by ...% to achieve λ= 1.
 
→ Display:
Read measured value block    8     ⇒
    2ms    -0.7 %    -0.5 %        TB active

Specified values =>Read measured value block - Page 01-83

  • ‒ If the specified values are not achieved =>Test table, Display group 08 - Page 01-84

Checking lambda probe heating > < Engine running problems after cold start