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Home >> Audi >> 1996 >> A6 Wagon (4A5) V6-2.8L (AFC) >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Testing and Inspection >> Scan Tool Testing and Procedures >> Scan Tool Testing >> Diagnosis With Scan Tool, Address Word 01 >> Read Measuring Block Values >> Display Group 045

Display Group 045

NOTE:

- Display group 045 is only assigned on vehicles with fuel tank system diagnosis and EVAP system diagnosis.
- All Audi A6 models have the new EVAP system/fuel tank diagnostic capability using the fuel system Leak Detection Pump (LDP) -V144-; component located in the right rear wheelhousing, under liner.
- If the value of the EVAP system diagnosis is not set to "0" in display group 029, display field 1 when creating the readiness code and/or there is a malfunction in the DTC memory that involves the tank system or EVAP system, display group 045 "Basic Setting" function 04, is used to carry out a selective diagnosis in the shop.

If the diagnosis conditions are fulfilled, the function testing of the tank system and EVAP system is carried out. The function testing consists of a leak test and a flow test which are carried out in individual steps.

Leak testing
During the leak diagnosis, the tank system and the EVAP system are closed off from the atmosphere. Then a de- fined over-pressure is built up using the fuel system leak detection pump -V144-. The ECM then checks how fast the pressure drops in the tank system and in the EVAP system. This is done by determining the position of a pump diaphragm using a reed switch. If the pump diaphragm is in rest position (reed switch closed), the reed switch supplies a voltage signal (approx. 12 - 14 volts) to the ECM. If the diaphragm is raised by vacuum, the reed switch opens and the voltage signal drops to approx. 0 volts. The time between raised pump diaphragm (0 V from the reed switch) and dropping pump diaphragm (12 volts from reed switch) is a measure of the leaks in the systems.

- The diagnosis time for the leak testing is displayed in display field 4.
- If a time greater than 8 sec. is recognized, a system with no leaks is assumed.
- If the time recognized is less than 1.15 sec., a large leak is assumed (rough leakage approx. 3 mm and greater).
- If a time between 1.15 and 1.5 sec. is recognized, a small leak is assumed (fine leakage approx. 1-3 mm).

Flow testing (function, EVAP canister purge regulator valve -N80-)
- Requirement for flow testing is passing the leak test.
- After ending the leak testing, the fuel system leak detection pump -V144- is triggered again with open EVAP canister purge regulator valve -N80-. The ECM then checks again how fast the pressure in the tank system and the EVAP system drops.
- The time for the pressure drop is a measure for the flow. If a time greater than 1.3 sec. is recognized, a malfunction is assumed in the EVAP canister purge regulator valve -N80-.






There are two methods for diagnosing the tank system and the EVAP system:

Vehicle diagnosis
Diagnosis conditions are reached during a drive of 80-100 km/h (50-63 mph) in 4th or 5th gear and/or selector lever position "D".

Diagnosis conditions for "Read Measuring Value Block" function 08, display group 045
- Engine control module coding OK
- No malfunctions stored in DTC memory
- Engine coolant temperature between 8-40°C (46-104°F)
- Vehicle speed less than 710 km/h (69 mph)
- Engine load less than 76%
- Altitude display less than 48 display group 001, display field 3

Shop diagnosis "Basic setting" function O4
Simplified shop diagnosis option using VAG 1551
Selective initiation of diagnosis with "Basic Setting" function 04, display group 045

Diagnosis conditions for "Basic Setting" function 04, display group 045
- Engine control module coding OK
- No malfunctions stored in DTC memory
- Vehicle off
- Closed Throttle Position (CTP) switch closed (throttle closed)

NOTE:
- If too much fuel vapor is present, the shop diagnosis can not be started. Corrective action: open fuel tank filler cap for approx. 1 min., close filler cap, start engine, initiate diagnosis.
- Shop diagnosis can only be initiated one time; before further diagnosis, the engine has to be started again.

Notes on display field 1:
Display field 1 shows what test the Engine Control Module (ECM) is carrying out at the moment.
Displayed value of "1" = Test 7: Reed switch closed?
- If reed switch is closed, diagnosis OK value "2"
- If reed switch is not closed, diagnosis not OK value "10"

Displayed value of "2" = Test 2: Does reed switch open? (Test 2 is carried out 3 times)
- If reed switch opens, diagnosis OK value "5"
- If reed switch does not open, diagnosis not OK check DTC memory

Displayed value of "5" = Test 5: Pumping phase for leak testing.
- Tank system and EVAP system are closed off from the atmosphere.
- Fuel system leak detection pump -V144- is triggered for approx. 35 sec. in order to build up over-pressure in tank system and EVAP system value "6"

Displayed value of "6" = Test 6: Leak testing
- ECM checks how quickly the over-pressure built up under value "5" drops in tank system and EVAP system.
- Tank system and EVAP system have no leaks value "7"
- Tank system and EVAP system leaks ~ carry out the leak testing a second time; if a leak is found again, check DTC memory and/or see malfunction codes P0442 / 16826 and/or P0455 / 16839.

Displayed value of "7" = Test 7: EVAP canister purge regulator valve -N80- is cycled (opens/closes) for approx. 100 sec., to insure accessibility and to reduce the overpressure that was built up by the leak testing value "8"

Displayed value of "8" = Test 8: Pumping phase for flow test

- Diagnostic Pump for Fuel System -V 144- is triggered approx. 35 sec. with EVAP canister purge regulator valve -N80- open value "9",

Displayed value of "9" = Test 9: Flow testing (testing function of EVAP canister purge regulator valve -N80-) ECM checks whether overpressure develops in the tank system and EVAP system.

- If no overpressure is recognized value "99"
- If overpressure is recognized check DTC memory and/or see malfunction code P0441/16825 Displayed value of "10" = Test 10: Leak testing and testing function of EVAP canister purge regulator valve -N80-
- Test 10 is only carried out if the diagnosis was not OK during test 1.
- During test 10, the EVAP canister purge regulator valve -N80- is opened for approx. 100 sec. in order to reduce any pressure than has built up in the tank. If the reed switch closes during this time, the system has no leaks and the EVAP canister purge regulator valve -N80- is OK
- If the reed switch does not close check DTC memory

Displayed value of "99" = Test 99: Diagnosis ended





Notes on display field 2: If the value "0" (testing not carried out yet or testing not OK) is displayed in display field 2, display field 3 can be used to recognize whether the test was not carried out yet or if it is not OK.
- Value "0" = Testing not carried out yet or testing not OK
- Value "1" = Testing OK





Notes on display field 3:
- Value "0" = Testing OK
- Value "7" = Testing not OK

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