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Checking additional signals > < Engine control unit

Leon Mk1

Checking Lambda probe and Lambda regulation after catalyst
Checking Lambda probe and Lambda regulation after catalyst
Only engine codes ANV, AUC, AUD, ANW
  Note!
Only gold-plated contacts may be used when servicing Lambda probe connector contacts 3 and 4.
Special tools and workshop equipment required
t  Fault reader -V.A.G 1551- or vehicle system tester -V.A.G 1552- with cable -V.A.G 1551/3A-
t  Test box -V.A.G 1598/22-
t  Hand multimeter -V.A.G 1526- or multimeter -V.A.G 1715-
t  Adapter set -V.A.G 1594-
t  Current flow diagram
Check conditions
   
l  All fuses must be OK.
l  The battery voltage must be at least 11.5 V.
l  Exhaust system between catalyst and cylinder head must be free of leaks
l  Coolant temperature must be at least 80 °C, ⇒ display group 04, display zone 3.
Functional check
–  Connect fault reader -V.A.G 1551- (-V.A.G 1552-). Start engine and select “Address word” 01 of engine control unit. When doing this the engine must be running at idling speed. (Connecting fault reader and selecting engine control unit → Vehicle diagnosis, testing and information system VAS 5051.)
  N24-0831
Indicated on display:
–  Press keys 0 and 4 for the function “Introduction of basic setting” and confirm entry with Q key.
  
Rapid data transfer                 HELP
Select function XX
Indicated on display:
–  Press keys 0, 3 and 7 for “Display group number 37” and confirm entry with Q key.
  
Basic setting                           
Input display group number XXX
Indicated on display: (1...4 = Display zones)
–  Depress brake pedal.
The engine speed is increased by the control unit to approx. 1100...1300 rpm.
–  Run engine at increased speed until the catalyst temperature increases to min. 400 °C.
  Note!
This process can take a few minutes.
–  Press C key.
The engine speed decreases to idling speed.
  
System in basic setting       37       →

      

      

    
      

      

    
Indicated on display:
– 
          Press keys 0, 3 and 0 for the “Display group number 30” and confirm entry with Q key.

      		 
      
    
Basic setting                           
Input display group number XXX          

      

      

    
      

      

    
Indicated on display: (1...2 = Display zones)
– 
          Check Lambda control status after catalyst (display zone 2): Specification: 1 1 1 (Significance  → Vehicle diagnosis, testing and information system VAS 5051)
 
      Note!
t 
           The first position of the 3 digit number block fluctuates between 0 and 1 (Lambda probe heating on and off).
t 
           Depending upon the status of the Lambda control the 3 digit number block can show 0 or 1.
t 
           The bits in display zone 1 will not be set to 1 until the catalyst temperature has exceeded 400.0 °C (⇒ display group 34, display zone 2).
If the specification is not obtained:
– 
          Check Lambda probe heating after catalyst  → Chapter.
If the specification is obtained:
– 
          Change to display group 36 as follows:
– 
          Press C key.

      		 
      
    
Read measured value block      30      →

      

      

    
      

      

    
Indicated on display:
– 
          Press keys 0, 3 and 6 for “Display group number 36” and confirm entry with Q key.

      		 
      
    
Basic setting                           
Input display group number XXX          

      

      

    
      

      

    
Indicated on display: (1...4 = Display zones)
– 
          Depress brake pedal.
The engine speed is increased by the control unit to approx. 1100...1300 rpm.
– 
          Check the Lambda probe voltage after catalyst in display zone 1: Specification: 0.000...1.000 V (can fluctuate slightly)
If the display in display zone 1 remains constant:
– 
          Press → key.
– 
          Press keys 0 and 6 for the function “End output” and confirm entry with the Q key.
– 
          Switch off ignition.
– 
          Continue check according to following table.

      		 
      
    
System in basic setting 36             →

      

      

    
Appears on displayPossible fault causeFault elimination
Constant 1.085 V
t 
           Short to positive via: Lambda probe, probe wiring, earth wiring, engine control unit
– 
          Check Lambda probe 2 basic voltage  → Anchor
– 
          Check Lambda probe wiring Lambda probe 2  → Anchor
Constant between
0.400...0.500 V
t 
           Open circuit via: Lambda probe, probe wiring, earth wiring, engine control unit
 
Constant 0.000 V
t 
           Short to earth via: Lambda probe, probe wiring, earth wiring, engine control unit
 


      

      

    
– 
          Run the engine at increased speed until the display in display zone 4 jumps from “Test OFF” to"Test ON. The catalyst temperature in display zone 2 must be min. 400 °C.
– 
          Maintain the increased engine speed until the display in display zone 4 shows the specification "B1-P2 OK.
 
      Note!
This process can take a few minutes.
If display zone 4 shows “B1-P2 n.OK”:
– 
          Press → key.
– 
          Press keys 0 and 6 for the function “End output” and confirm entry with the Q key.
– 
          Check exhaust system for leaks:  → Chapter
– 
          Carry out a test drive to remove possible residue on Lambda probe and repeat check.
Observe the valid safety precautions when carrying out a road test  → Chapter.
If the specifications are again not attained:
– 
          Replace the Lambda probe after catalyst -G130- → Item.
Checking Lambda probe 2 basic voltage

      		 
      
     
      

      

    
      

      

    
– 
          Separate 4-pin connector (black) to Lambda probe after catalyst -G130--arrow-.

      		 
      
    N24-0906
      

      

    
      

      

    
– 
          Connect multimeter with aux. cables from -V.A.G 1594- to measure voltage at contacts 3+4 (connector to engine control unit).
– 
          Start engine and measure the basic voltage. Specification: 0.400...0.500 V
– 
          Switch off ignition.
If the specification is not obtained:
– 
          Check Lambda probe wiring for Lambda probe 2  → Anchor.
If the specification is obtained:
– 
          Replace the Lambda probe after catalyst -G130- → Item.
Checking Lambda probe wiring Lambda probe 2
– 
          Remove wiper arms and cowl panel:  → Electrical system; Rep. Gr.92

      		 
      
    N24-0731
      

      

    
      

      

    
– 
          Connect test box -V.A.G 1598/22- to control unit wiring harness.

      		 
      
    N24-0709
      

      

    
      

      

    
– 
          Check wires between test box and 4-pin connector (connector to control unit) for open circuit using current flow diagram. Contact 3+socket 21 Contact 4+socket 47 Wire resistance: max. 1.5 Ω
– 
          Check wiring at connector contacts 3+4 for short circuit to contacts 1+2 using current flow diagram. Specification: ∞ Ω
If no fault is detected in the pipes:
– 
          Replace the Lambda probe after catalyst -G130- → Item.

      		 
      
    A24-0094
      

      

    


Checking additional signals >
< Engine control unit