Oxygen Sensor System Adaptation
Diagnosis of the Oxygen Sensor (O2S) System adaptation
The adaptive O2S system corrects longer lasting deviations of the fuel/air mixture of Lambda = 1 by changing the anticipatory control calculated in the ECM and with that the changed injection timing.
The participatory control is changed multiplicatively and additively via the fuel/air mixture adaptation in such a way, that the corrections of the oxygen sensors (FR) can be kept small so that even during unregulated operation, the fuel/air mixture is close to Lambda 1.
The procedure is based on the following assumptions:
Over the life span of the engine and through different tolerances, two basic faults may occur: the multiplicative fault and the additive fault per time unit (false air). During idle the false air fault dominates (low air ratio, low rpm), at high air ratio the multiplicable fault dominates.
A fault combination of multiplicable and additive nature is compensated correctly when a corrective value in its dominant area is adapted.
Therefore there are two adaptation areas: the adaptation in the idle segment and the adaptation under load.
Area 1: Sector near idle = TRA
Area 2: Load sector = FRA
System description:
After dialing the adaptation values for the 02S System, the following displays may appear:
Area 1:
TRA: xxx
TRA2: xxx
Button 1 or N
Explanation:
TRA: = Adaptation in idle sector for cylinders 1 - 3
TRA2: = Adaptation in idle sector for cylinders 4 - 6
Area 2:
xxx
FRA2: xxx
Button 1 or N
Explanation:
FRA: = Adaptation under load for cylinders 1 - 3
FRA2: = Adaptation under load for cylinders 4 - 6
Oxygen sensor:
FR:
FR2:
Button 1 or N
Explanation:
FR: = Oxygen sensor (integrator) cylinders 1 - 3
FR2: = Oxygen sensor (integrator) cylinders 4 - 6
Function: After the ECM was disconnected from constant plus, the numerical values are at 1.00 (FRA) or 0 (TRA). After starting the engine first the programmed channel is displayed.
Example:
Area 1:
TRA: 0
TRA2: 0
Button 1 or N
After release of the 02S system (depending on engine temperature) the oxygen sensor (FR) moves at about its mean value(for example 0.98 - 1.03).
Example:
O2S system:
FR: 1.03
FR2: 1.02
Button 1 or N
If the engine at this stage runs too lean (for example through addition of 10% of false air), the value FR (oxygen sensor) will deviate by this value from the mean value (by 1.10), to compensate for the false air. Now the fuel/air mixture is again within Lambda 1 and in spite of 10% false air, the 025 System operates at 1.11.
Example:
O2S system:
FR: 1.09
FR2: 1.11
Taste 1 or N
Because the range of the 02S System is limited, the adaptation needs to relieve the 02S system after a few minutes to make the full range again available.
At that time the TRA (at idle) shifts up in area 1 in the area 1, i.e. time is added for injection until the FR is again working at about its mean value. At the TRA-value the scan tool shows the added time in milliseconds.
Example:
Area 1:
TRA: 0.165
TRA2: 0.167
Button 1 or N
Should the adaptation phase under load run out (in area 2) the FRA value would change. It would be displayed by the scan tool in %.
Example:
Area 2:
FRA: 1.06
FRA2: 1.07
Button 1 or N
Since, however, the false air of 10% has a greater affect during idle than under load, the FRA-value changes as long as the 02S System moves at about its mean value.
The changes through adaptation in TRA (area 1) or in FRA (area 2) affect also the other adaptation area. This way the adaptation data with false air of 10% and after running through the various adaptation areas may look like this:
Example:
Area 1:
TRA: 0.165
TRA2: 0.167
Button 1 or N
or:
Area 1:
FRA: 1.06
FRA2: 1.07
Button 1 or N
The maximal adjustment of the 02S System is 25% in the direction toward rich and 25% toward lean. Therefore an incorrect fuel/air mixture can be briefly corrected by the 02S System in the direction of rich as well as in the direction of lean. For corrections of longer duration, the adaptation takes care of the correction. This correction factor remains stored in the ECM until the ECM is disconnected from permanent plus.
Changes in the fuel/air ratio caused by fuel tank ventilation is corrected by an additional adaptation factor (FTEA).
This way the adaptation value for fuel tank ventilation (FTEA) at high absorption of the EVAP Canister could look like this:
Example:
Fuel tank ventilation:
FTEA: 0.93
Button 1 or N
Between the individual adaptation phases, which could be at intervals of 250 sec. or 650 sec. and which are dependent on the last applicable correction factor, a purge phase for the EVAP Canister is programmed.
Should the corrections for the fuel/air mixture caused by the adaptation be so large that it reaches the adaptation threshold a fault will be recorded in the ECM.
NOTE: Map changes at full load (FRA) react multiplicatively, map changes in the idle range (TRA) react additively.