Diagnostic Trouble Codes with Test Charts (V8): Other BMW X5 E53 рестайлинг

Monitoring Structure

According to the operating principle described above the following main parts of the monitor can be distinguished

1. Monitoring the amount of removed oxygen after fuel cut-off
2. Check of monitoring conditions for active test
3. Lambda request (interface to lambda control)
4. Mixture enrichment in order to remove any stored oxygen
5. Measurement of oxygen storage capacity (OSC) by lean A/F operation
6. Fault detection

Monitor structure overview

Scheme 325

Lambda Request

The monitor requests a richer or leaner A/F ratio via the mixture control.

Mixture Enrichment

The engine is operated at a low A/F ratio ( <1) in order to remove any stored oxygen from the catalyst.

Fault Detection

If the passive test detects a storage capacity significantly above the borderline limit, the catalyst is determined to be good and the monitoring is complete. If the passive test does not meet the condition for a good catalyst, the active test is initiated and the OSC is calculated. The catalyst is diagnosed by comparing the determined OSC against the borderline threshold.

Monitoring conditions for active test

1. no faults with the lambda sensors (signal, aging, heater)
2. canister purge value < limit
3. no error on EGR system (if available)
4. modeled catalyst temperature within range
5. misfire rate < limit
6. regular A/F control (not in fuel cut-off)
7. engine air mass flow within range

Scheme 326

Data Acquisition

The durations of the crankshaft segments are measured continuously for every combustion cycle.

Sensor Wheel Adaptation

Within a defined engine speed range and during fuel cut-off, an adaptation of the sensor wheel is carried out to compensate for manufacturing tolerances.

This process is repeated for additional engine speed ranges until the total operation range of the engine has been adapted. Then the maximum sensitivity to engine misfire is achieved.

Misfire Detection

The following operating steps are performed for each measured segment corrected by the sensor wheel adaptation.

Calculation Of Engine Roughness

The engine roughness is derived from the differences of the segment durations.

Different statistical methods are used to distinguish between normal changes of the segment duration and the changes due to misfiring.

Detecting Multiple Misfiring

If several cylinders are misfiring (e.g. alternating one combustion/one misfire event) the calculated engine roughness values may be so low, that the threshold is not exceeded during misfiring and therefore misfiring would not be detected.

Based on this fact, the periodicity of the engine roughness value is used as additional parameter during multiple misfiring. The engine roughness value is filtered and a new multiple filter value is created. If this filter value increases due to multiple misfiring, the roughness threshold is decreased. By applying this strategy, multiple misfiring is detected reliably.

Calculation Of Engine Roughness Threshold Value

The engine roughness threshold value consists of the base value, which is determined by a load/speed dependent map.

During warm-up a coolant temperature dependent correction value is added. In case of multiple misfiring the threshold is reduced by an adjustable factor.

Without sufficient sensor wheel adaptation the engine roughness threshold is limited to a speed dependent minimum value.

A change of the threshold towards a smaller value is limited by a variation constant.

Determination Of Misfiring

A misfire determination is made by comparing the engine roughness value to the engine roughness threshold value.

If a misfire event is detected in a cylinder, the misfire detection of the next cylinder in the firing order is deactivated to prevent a false diagnosis.

Statistics And Fault Processing

Within an interval of 1000 crankshaft revolutions the detected misfiring events are added for each cylinder. If the sum of all cylinder misfire incidents exceeds a predetermined value, a pending code for emission relevant misfiring is stored. If only one cylinder is misfiring, a cylinder specific fault code is stored. If more than one cylinder is misfiring, the fault code for multiple misfiring is also stored.

Within an interval of 200 crankshaft revolutions the detected number of misfiring events is weighted and calculated for each cylinder. The weighting factor is determined by a load - and speed-dependent map.

If the sum of cylinder misfire events exceeds a predetermined value the fault code for catalyst damage relevant misfiring is stored and the MIL is illuminated at once (blinking).

If the cylinder specific count exceeds the predetermined threshold the following measures take place

1. the fuel control switches from closed-loop to open-loop operation
2. a cylinder specific fault code is stored. If more than one cylinder is misfiring, the fault code for multiple misfire is also stored
3. the fuel supply to the respective cylinder is cut-off

All misfire counters are reset after each interval.

Statistics: Fault Processing

Scheme 327

Evaporative Purge System Flow Check

The purge flow from the charcoal canister is monitored after the fuel system adaptation is completed and the lambda controller is in closed loop operation. The diagnosis is started during regular purging.

Scheme 328

Step 1 - For Rich Or Lean Mixture

Flow through the purge valve is inferred as soon as the lambda controller compensates for a rich or a lean shift.

After this procedure the diagnosis is completed and the evaporative purge system resumes normal operation.

Step 2 - For A Stoichiometric Mixture

In this case the lambda controller does not need to compensate for a deviation. Therefore, after finishing the regular purging, the purge valve is opened and closed abruptly several times.

The effect of additional intake charge causes a variation of the engine idle speed. If the variation reaches a predetermined value, the system is deemed to be functioning properly and the diagnosis procedure is completed.

To start the diagnosis function (step 2) several conditions have to be satisfied.

1. vehicle speed = 0
2. engine at idle speed
3. closed loop of fuel system controller
4. coolant temperature > fixed limit

Furthermore if the diagnosis has already been started and one of the conditions has not been satisfied continuously, the process will be interrupted and started again later.

1. engine idle speed variation < fixed limit

Step 3

In case of a high load at idle, a variation of the engine idle speed cannot be measured correctly in Step 2.

Therefore, an additional check is performed by opening the purge valve after the EVAP leak detection has finished.

When the purge valve opens, the pressure in the tank system drops as does the DM-TL pump current.

If pump current > threshold, the purge valve is considered operational.

Mixture Pilot Control

The intake air mass flow rate and the engine speed are measured. These signals are used to calculate an injection signal. This mixture pilot control follows fast load and speed changes.

Lambda-Controller

The ECM compares the oxygen sensor signal of the upstream sensor with a reference value and calculates a correction factor for the pilot control.

Adaptive Pilot Control

Drifts and faults in the fuel system sensors and actuators as well as undetected air leakage influence the pilot control. This causes increasing deviations of the air/fuel ratio. The adaptive pilot control effects the controller correction in two different ranges.

Scheme 329

Lambda deviations in range 1 are compensated by an additive correction value multiplied by an engine speed term. By this an additive correction per time unit is created.

Lambda deviations in range 2 are compensated by a multiplicative factor.

A combination of both ranges will be correctly separated and compensated.

Each value is adapted in its corresponding range only. But each adaptive value corrects the pilot control within the whole load/speed range. At the next start the stored adaptive values are included in the calculation of the pilot control just before the closed loop control becomes active.

Offset Check

The offset check monitors for an incorrect lambda measurement due to shunting effects. If the lambda-offset of downstream control exceeds a threshold, a fault code is set.

Heater Coupling Check

The heater coupling check monitors low impedance coupling between the heater and the sensor elements, which can cause lambda modulations with heater pulse rate. If the difference of consecutive lambda values exceeds threshold, a fault code is set.

Dynamics Checks (Slow Response)

Due to aging, sensor dynamic response can decrease.

The dynamics check in normal operation mode compares measured and estimated (model-based) lambda-behavior, caused by artificial lambda modulation. If the ratio of measured and estimated amplitude is below the threshold, a fault code is set.

Plausibility Check

1. Wide-Range oxygen sensor is not active: If lambda value is close to 1.0 for a period of time, a fault code is set. Monitoring conditions for plausibility check: downstream oxygen sensor voltage indicates lean or rich mixture
2. Sensor current high ( LSU lean): If lambda value exceeds a threshold, but downstream oxygen sensor indicates rich mixture, a fault code is set.
3. Sensor current high ( LSU rich): If lambda value is below a threshold, but downstream oxygen sensor indicates lean mixture, a fault code is set.

Scheme 330

Resistance Check

The internal resistance (Ri) depends on the ceramic temperature. The ceramic temperature is influenced by the electrical heater and the exhaust gas temperature.

For the heater monitor the resistance of the ceramic is measured and compared to a reference value depending on heater power and exhaust gas temperature.

Engine Control Module (ECM) Input/Output Signals Table

ENGINE CONTROL MODULE (ECM) INPUT / OUTPUT SIGNALS

Transmission Control Module (EGS) Input/Output Signals Table

TRANSMISSION CONTROL MODULE (EGS) INPUT / OUTPUT SIGNALS REFERENCE

TRANSMISSION CONTROL MODULE (EGS) INPUT / OUTPUT SIGNALS REFERENCE