Checking CO2 content in exhaust gas: Audi Q7

🧭 Before you start

Fits: Audi Q7 (4L, 2005–2015)

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

Don't miss

• The hose (B) of the exhaust probe must not stop exhaust gas emerging from the exhaust pipe (A) during the test.
• The instantaneous operating status of the auxiliary/supplementary heater can be seen from the measured value block "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
• Once the auxiliary/supplementary heater has switched to full load mode, wait at least another 1 minute (approx. 3 or 5 minutes after activation, depending on version, the auxiliary/supplementary heater must be in full load mode).

📋 Procedure

1. With the ignition switched off, connect up the vehicle diagnostic, testing and information systemVAS 5051 A, for example, with the diagnostic cableVAS 5051/5A to the 16-pin diagnosis socket in the vehicle "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
2. Switch ignition on and all electrical equipment off.
3. Start engine and switch off all electrical equipment. [Note: Auxiliary/supplementary heater self-diagnosis can only be started with the ignition switched on (the data bus diagnostic interface J533 is only active when the ignition is on). Once the auxiliary/supplementary heater has switched to diagnosis mode, auxiliary/supplementary heater self-diagnosis can be continued even with the ignition switched off. On diesel vehicles with supplementary heater (with no "“auxiliary heater”" as optional extra), the ignition must be left switched on, as otherwise self-diagnosis will be terminated.]
4. Select the "“Guided fault-finding”" function "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
5. Read out the event recorders of all systems with self-diagnosis capability, paying particular attention to the following vehicle systems "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051:

6. Eliminate the cause of any faults displayed in the vehicle systems and erase the event recorder "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
7. Select the supplementary heater control unit J364 in the "“guided fault-finding”" function "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
8. Switch on the exhaust emission test stationVAS 6300 and insert the appropriate exhaust probe hose (B) in the auxiliary/supplementary heater exhaust pipe (A). [Note: The hose (B) of the exhaust probe must not stop exhaust gas emerging from the exhaust pipe (A) during the test.]
9. Set maximum heat output on the front operating and display unit, Climatronic control unit J255.
10. Restrict the fresh air blower speed by setting the front operating and display unit to approx. 50 % of the maximum fresh air blower speed.
11. On vehicles with "“auxiliary heater”" as optional extra, switch on the auxiliary/supplementary heater by way of the front operating and display unit, Climatronic control unit J255Owner's manual or e.g. via the Vehicle diagnostic, testing and information system ("“Basic setting”" function) "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
12. On vehicles with diesel engine with supplementary heater and no "“auxiliary heater”" as optional extra, switch on the supplementary heater e.g. by way of the vehicle diagnostic, testing and information system ("“Basic setting”" function) "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. [Note: On vehicles with diesel engine and supplementary heater (with no "“auxiliary heater”" as optional extra), it may be necessary before switching on the supplementary heater by way of the "“Basic setting”" function to start the engine or, as of a coolant temperature in excess of 40 °C, to switch on the ignition and set the air conditioner to "“Hi”".]
13. Wait until the auxiliary/supplementary heater switches from starting to full load mode (approx. 2 or 4 minutes depending on version). [Note: The instantaneous operating status of the auxiliary/supplementary heater can be seen from the measured value block "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.]
14. Once the auxiliary/supplementary heater has switched to full load mode, wait at least another 1 minute (approx. 3 or 5 minutes after activation, depending on version, the auxiliary/supplementary heater must be in full load mode).
15. Read off the measured value for the CO2 (carbon dioxide) content of the exhaust gas from the CO2 measuring instrument. [Note: The hose (B) of the exhaust probe must not stop exhaust gas emerging from the exhaust pipe (A) during the test.] [Note: If the measured value is in the lower range (less than 9%), problems may be encountered with auxiliary/supplementary heater combustion under unfavourable usage conditions (e.g. high vehicle speed with auxiliary/supplementary heater switched on). Set the CO2 content in the exhaust gas to a higher value .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.]
16. 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 .
17. Check the fuel delivery rate of the metering pump V54.
18. If the CO2 content of the exhaust gas and the fuel delivery of the metering pump V54 are in the lower specified range, replace the metering pump V54.
19. 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 .
20. Check the combustion air blower V6"Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and .
21. Adjust the CO2 content of the exhaust gas "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and .
22. If the CO2 content of the exhaust gas cannot be adjusted, replace the combustion air blower V6.
23. Check the glow plug with flame monitor Q8"Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051 and .

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