Audi Workshop Service and Repair Manuals

Special tools and workshop equipment required

• ◆ V.A.G 1526 A
• ◆ V.A.G 1594 A
• ◆ V.A.G 1598/31
• ◆ V.A.G 1788/10
• ◆ VAS 5051 with VAS 5051/1

• or

• ◆ V.A.G 1551 with V.A.G 1551/3 A

Note:

The lambda control after catalytic converter serves as a correction control.

→ It corrects slight mixture changes (e.g. enriches) through the lambda probe before catalytic converter, by maintaining the lambda control for a certain period (dwell time) at the upper / lower point. If the time is in the positive range (e.g. 50 ms), the mixture is made richer. If the time is in negative range (e.g. -50 ms), the mixture is made leaner.

Fitting location of connectors .

Test conditions

• ● Test drive vehicle and do not erase fault memory.
• ● Coolant temperature at least 85 oC (display group 4, display zone 3)

Test sequence

• ‒ Connect up vehicle diagnostic, testing and information system VAS 5051 or fault reader V.A.G 1551 and select engine electronics control unit with "Address word" 01 => Page 01-8.
  For this purpose, the engine must be running at idle speed

• ‒ Enter "04" to select "Start basic setting" and confirm with Q key.

Note:

During basic setting, the solenoid valve for the active carbon canister (valve -N80) is closed and the air conditioner compressor is switched off.

• ‒ Enter "034" for "display group number 034" and confirm entry with Q key.

• ‒ Set engine speed to 2800...3200 rpm using engine speed controller V.A.G 1788/10.
• ‒ Perform the test as soon as an exhaust gas temperature above 320 oC is attained in display zone 2.

Note:

This process can take a few minutes.

• ‒ Press C key.
• ‒ Set engine speed to 1900...2200 rpm using engine speed controller V.A.G 1788/10.

• ‒ Enter "030" for "display group number 030" and confirm entry with Q key.

• ‒ Check lambda probe status for lambda probe after catalytic converter in display zones 2 and 4.

Note:

The "lambda probe status" indicates the condition of the lambda control and the lambda probes.

Notes:

• ◆ The lambda control of lambda probe after catalytic converter (bank 1-probe 2 and bank 2-probe 2) is not active without engine load, i.e. the display is 0.
• ◆ The first digit of the 3-digit display (heating) fluctuates between 0 and 1.
• ◆ The third digit of the 3-digit display (lambda control) fluctuates between 0 and 1.

Significance of 3-digit readout of display group 30

• ‒ Press C key.

• ‒ Enter "043" for "display group number 043" and confirm entry with Q key.

Test conditions

• ● Engine runs at 1900...2200 rpm.

• ‒ Check specified value in display zone 4:

If specified value "B1-P2 OK" is attained:

• ‒ Press C key.

Test conditions

• ● Engine runs at 1900...2200 rpm.

• ‒ Press keys 0, 4 and 4 for "display group number 44" and confirm entry with Q key.

If specified value "B2-P2 OK" is attained:

• ‒ Press C key.

Checking lambda control after catalytic converter

• ‒ Carry out a test drive lasting at least 10 minutes.

• ‒ Enter "037" for "display group number 037" and confirm entry with Q key.

• ‒ Check lambda probe voltage in display zone 2.
• ‒ Check dwell time between lambda probe 1 before catalytic converter and lambda probe 2 after catalytic converter in display zone 3 and diagnosis result in display zone 4.

Note on display zone 3:

The lambda control after catalytic converter serves as a correction control. It corrects slight rich / lean mixture changes of the lambda probe before converter, by maintaining the lambda control before converter for a certain period (dwell time) at the upper / lower point. If the time is in positive range (e.g. 50 ms), the mixture is made richer. If the time is in negative range (e.g. -50 ms), the mixture is made leaner.

• ‒ Press C-key.
• ‒ Press keys 0, 3 and 8 for "display group number 38" and confirm entry with Q key.

Note on display zone 3:

The lambda control after catalytic converter serves as a correction control. It corrects slight rich / lean mixture changes of the lambda probe before converter, by holding the lambda control before converter for a certain period (dwell time) at the upper / lower point. If the time is in positive range (e.g. 50 ms), the mixture is made richer. If the time is in negative range (e.g. -50 ms), the mixture is made leaner.

Evaluation of display groups 037 and 038

(cont.)

If specified value in display group 37 and 38, display zone 3 or 4 is not attained:

• ‒ Check for air leak at exhaust or catalytic converter (check screw clamps and exhaust for damage)
• ‒ If values of display zones 3 differ greatly (e.g. +500 ms, -500 ms) (lambda correction value) in measured value blocks 37 and 38, the lambda probes after catalytic converter of cylinder bank 1 and 2 could be mixed.

If none of the given causes apply:

• ‒ Replace respective lambda probe
  "pre" catalytic converter.