Adjusting CO2 content in exhaust gas: Audi Q7

🧭 Before you start

Fits: Audi Q7 (4L, 2005–2015)

• Special tools named: VAS 5051
• Renewed: these components

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• There may be several reasons for the display "“Function unknown or cannot be implemented at present”" appearing in the display zone "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
• The hose (B) of the exhaust probe must not stop exhaust gas emerging from the exhaust pipe (A) during checking and adjustment.
• Read the measured value for the CO2 (carbon dioxide) content in the exhaust gas off the CO2 measuring instrument (as of approx. 1 minute after the last entry, the auxiliary/supplementary heater must be in full load operation).

📋 Procedure

1. Check the CO2 (carbon dioxide) content in the exhaust gas of the auxiliary/supplementary heater . [Note: Necessary test requirements satisfied Adjustment can only be made if the auxiliary/supplementary heater has been operating in full load mode for at least one minute.Adjustment of the CO2 content in the exhaust gas requires connection of the vehicle diagnostic, testing and information systemVAS 5051 A to the vehicle and initiation of auxiliary heater guided fault-finding "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.Adjustment of the CO2 content in the exhaust gas requires the CO2 measuring instrument to be ready for operation and the exhaust measurement probe (B) to be fitted in the exhaust pipe (A) of the auxiliary heater such that it does not stop exhaust gas emerging.If the auxiliary heater switches from full to part load operation during CO2 adjustment on account of an excessive coolant temperature, full load operation of the auxiliary heater can be maintained up to a coolant temperature of approx. 110°C and for max. approx. 10 minutes in the "“Basic setting”" function. If this period is not sufficient, the procedure can be repeated "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.Alteration of the CO2 content of the exhaust gas involves changing the actuation voltage for the combustion air blower V6 by way of the "“Adaption”" function "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051..]
2. Exit from the "“Basic setting”" function if this function has been used to activate the auxiliary/supplementary heater.
3. Select the "“Adaption”" function "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
4. Use the input keypad to enter the adaption channel for adjusting the "“CO"2 content in the exhaust gas” and confirm the entry "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. [Note: There may be several reasons for the display "“Function unknown or cannot be implemented at present”" appearing in the display zone "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.]
5. Wait until the auxiliary/supplementary heater switches to full load mode.

6. Switch off the auxiliary/supplementary heater by way of the front operating and display unit, Climatronic control unit J255 and on again using the Vehicle diagnostic, testing and information system ("“ Basic setting”" function). In this setting, full load operation is then possible up to a coolant temperature of 110 °C "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. [Note: On vehicles with a diesel engine and supplementary heater (no "“auxiliary heater”" as optional extra), it may be necessary to switch off the engine and wait for the coolant to cool down sufficiently. Adjustment work can then be performed without interruption with the engine running or with the ignition switched on (coolant temperature at least 40 °C and air conditioner set to "“Hi”").]
7. Read the measured value for the CO2 (carbon dioxide) content in the exhaust gas off the CO2 measuring instrument (as of approx. 3 or 5 minutes after switch-on, depending on version, the auxiliary heater must be in full load operation). [Note: The hose (B) of the exhaust probe must not stop exhaust gas emerging from the exhaust pipe (A) during checking and adjustment.]
8. Use the input keypad in the display zone to alter the value for this adaption channel for re-adaption of the supplementary heater control unit J364 and thus the CO2 content in the exhaust gas "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. [Note: The CO2 content changes by approx. 0.05 % by vol. per unit.Display value higher, CO2 content lower or display value lower, CO2 content higher.With the supplementary heater control unit J364 fitted at present, a value between "“100”" and "“250”" can be entered. Values entered via the keypad or bar which are not within the specified limits are displayed but not implemented.If the value entered is too high or too low, the display is automatically reset to the initial value or to the lowest/highest value still permitted.The value applicable prior to adjustment remains stored if the auxiliary/supplementary heater is shut off during the "“Adaption”" function (CO2 adjustment). The procedure is then to be repeated.]
9. Adopt and store the entry "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. [Note: If the CO2 content in the exhaust gas is to be increased, a lower value must be entered in the adaption channel (the combustion air blower V6 is actuated at a slightly lower voltage and less air is thus conveyed to the combustion chamber).If the CO2 content in the exhaust gas is to be reduced, a higher value must be entered in the adaption channel (the combustion air blower V6 is actuated at a higher voltage and more air is conveyed to the auxiliary heater).If the value in the adaption channel is increased by 10 units, the CO2 content of the exhaust gas decreases by approx. 0.5 % by vol.]
10. Read the measured value for the CO2 (carbon dioxide) content in the exhaust gas off the CO2 measuring instrument (as of approx. 1 minute after the last entry, the auxiliary/supplementary heater must be in full load operation).
11. Repeat the adjustment procedure.
12. Switch off the auxiliary/supplementary heater.
13. Terminate self-diagnosis and unplug the diagnostic connector. [Note: If the auxiliary/supplementary heater has been switched on via the "“Basic setting”" function, it can also be switched off again by way of the "“Basic setting”" function "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.If the value displayed by the CO2 analyser fluctuates slightly, form the mean from the highest and lowest measured value.If the value displayed by the CO2 measuring instrument fluctuates considerably (more than approx. +/- 0.6% depending on measuring instrument), check the position of the measurement probe in the auxiliary/supplementary heater exhaust pipe.]
14. Check the intake air silencer and the auxiliary/supplementary heater exhaust system for contamination or cross-sectional constriction and clean or replace these components if necessary and .
15. Check the fuel delivery rate of the metering pump V54.
16. Check the combustion air blower V6"Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and .
17. Dismantle the auxiliary/supplementary heater and clean the combustion chamber. If there are no significant deposits in the combustion chamber, replace the combustion air blower V6.

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