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Checking lambda probe heating > < Poor performance after cold start

A3 Mk1

Motronic Injection and Ignition System (4-cyl.)
Testing lambda control
Testing operation
  • ‒ Select the function "Read measured value block" (function 08) and Display Group 03
    .
 
→ Indicated on 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°C.

  • ‒ Press C key.
  • ‒ Press keys 0 and 7 for "Display group number 07" and confirm entry with Q key.
 
→ Indicated on display:
Read measured value block 7    ⇒
    1    2    3    4

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

  • ‒ If the lambda probe voltage reading fluctuates very slowly, test the lambda probe heating => Page 24-44.
  • ‒ If the display shows a constant lambda probe voltage reading of between 0.45 and 0.50 V, this means there is an open circuit in the signal wiring. Test wiring => Page 24-46.
  • ‒ If the display shows a constant voltage reading of between 0.0 and +0.3 V (mixture too lean), this means that the lambda control has reached the maximum enrichment limit but the lambda probe is still registering "Mixture too lean".
  • ‒ If the display shows a constant voltage reading of between +0.7 and 1.0 V (mixture too rich), this means that the lambda control has reached the maximum leaning-down limit but the lambda probe is still registering "Mixture too rich".
  • ‒ Press C key.
  • ‒ If the lambda probe is functioning properly, check the lambda learned values.
  • ‒ Press keys 0 and 8 for "Display group number 08" and confirm entry by pressing Q.
 
→ Indicated on display:
Read measured value block 8    ⇒
    2ms    -0.7 %    -0.5 %    TB active

The mixture adaption system has learning ability, i.e. the lambda control can recognise differences between engines (injector nozzle delivery, cylinder compression, fuel pressure, etc.) and compensates by adjusting the pre-programmed basic injection periods mapped in the control unit. The injection periods are extended or reduced until "λ = 1" mixture composition is achieved. The difference between the actual injection period and the original period mapped in the control unit is given as a percentage.

  • ◆ Positive learned value (+...%): Pre-programmed basic injection period too short, actual injection period ...% longer in order to achieve "λ = 1" mixture composition.
  • ◆ Negative learned value (-...%): Pre-programmed basic injection period too long, actual injection period ...% shorter in order to achieve "λ = 1" mixture composition.

Specifications: => Page 01-110.

Checking lambda probe heating > < Poor performance after cold start