Self Diagnosis - Theory & Operation (N12): Other MINI Cooper I

1. Catalyst monitoring

(P0420)

The diagnosis of the catalyst directly determines the oxygen storage capacity (OSC) of the catalyst and compares the result with that of a borderline catalyst i.e. a catalyst deteriorated to the malfunction criteria. The nonlinear correlation between conversion efficiency and oxygen storage capacity has been shown in various investigations.

Scheme 113

1.2 Catalyst check

The catalyst check is based on the direct measurement of its OSC during the transition from a rich to a lean air-fuel mixture. The required set up is depicted in (Scheme 113). The air-fuel ratio can be precisely determined with the front oxygen sensor. The rear oxygen sensor delivers information about the OSC of the catalyst. In a two step process oxygen is first completely flushed out of the catalyst with a rich air-fuel mixture. The rear oxygen sensor indicates this with a voltage signal that is greater than a calibrated value. In the second step a lean air-fuel mixture is flushed into the catalyst and the amount of oxygen stored is calculated 1 right up to the oxygen overflow point.

1 OSC(t) = air mass flow * [(normalized A/F ratio) -1] * dt

Oxygen overflow is indicated by a drop in voltage (below a calibrated minimum) of the rear oxygen sensor's signal. This two step process is repeated within the driving cycle for at least a calibrated number of times before the results are evaluated.

Scheme 114

1.3 In-use monitoring performance ratio (IUMPR)

The incriminating of the numerator, the denominator and the ratio calculation for the catalyst monitor is executed by the IUMPR kernel function. Like all monitors for which a standardized track and report in-use performance is required, the catalyst monitor reports to the IUMPR kernel function via status flags.

2 Misfire detection

(P0300, P0301, P0302, P0303, P0304)

The misfire monitor is designed to detect combustion misfire by evaluating engine (crankshaft) speed fluctuations. The entire function for misfire detection consists of various sub-functions which together guarantee complete detection of misfire according to legislative requirements (graphical description (Scheme 115)).

The diagnostic starts with the calculation of a segment duration from the crankshaft signal, and correcting it with a self-learning sensor wheel adaptation (fuel-off adaptation). Engine speed fluctuation values are then calculated and again corrected by an extended adaptation (fuel-on adaptation). The misfires detected by the individual methods luts, dluts and fluts are linked together and further processed in the fault code management. The fault code management determines appropriate fault code reporting and MIL action if required.

Scheme 115

2.1 Segment time formation (%DMDTSB)

The core of the method is the precise sensing of engine speed. This is performed by scanning the 60-less-2-toothed sensor wheel by means of an inductive sensor. The ECU reads the sensor signal and calculates the duration of the crankshaft segments. The time required for each crankshaft segment to travel past the inductive sensor is referred to as the segment time ts(n) , where n is the combustion index. Its length corresponds to the interval between two ignitions.

2.2 Correction of the segment time ts(n) (%DMDFOF (Scheme 116))

The adaptation during fuel cut-off learns systematic differences of the segment durations between the individual segments and uses the determined correction values to compensate segment specific variations. After the adaptation being completed, the segment durations are nearly identical apart from the stochastic signal noise in the steady-state case.

Scheme 116

2.3 Calculation of the engine roughness values luts, fluts and dluts (%DMDLFB)

The engine roughness luts (angular acceleration) for each combustion is calculated from several temporarily consecutive segment durations as follows

Scheme 117

Where the segment length is 180°. The compensation time tkomp(n) is made in the calculation for normal engine operation involving accelerations and decelerations.

dluts is calculated by subtracting of luts values staggered by 360°crankshaft: (one revolution of the crankshaft).

Scheme 118

For fluts the cylinder-individual engine roughness values luts(cyl) are filtered by means of a recursive low pass (fluts(cyl))

Scheme 119

2.4 Determination of the engine roughness correction value (%DMDFON (Scheme 120))

The adaptation during firing operation (fuel-on adaptation) compares the calculated engine roughness luts of the individual cylinders and learns systematic deviations. These are stored in a speed- and load dependent map.

Scheme 120

2.5 Fuel-on correction of engine roughness values luts, fluts & dluts (%DMDLFK)

The learned fuel-on adaptation values are used to correct the engine roughness values of luts, dluts and fluts in order to improve the overall signal-to-noise ratio.

2.6 Misfire detection by luts-method (%DMDLU (Scheme 121))

The corrected engine roughness lutsk is compared to a load and speed dependent threshold lurs. If the threshold is exceeded, misfire is detected. An example of continuous misfire in cylinder one is (Scheme 122)

Scheme 121

Scheme 122

2.7 Misfire detection by dluts-method (%DMDDLU (Scheme 123))

This function allows the detection of random and continuous misfire, as well as non-symmetrical multiple misfire. Due to the 360°CS staggered value dlutsk the detection quality is independent of sensor wheel inaccuracies (crankshaft-synchronous segment time fluctuations). However, symmetrical multiple misfires (which also generate crankshaft-synchronous segment time fluctuations) can not be detected. dlutsk is compared to a load and speed dependant threshold dlurs . Misfire is detected if the threshold is exceeded.

Scheme 123

2.8 Misfire detection by fluts-method (%DMDLUA (Scheme 124))

The function allows the detection of continuous misfire at one or more cylinders. The filtered, cylinder-individual engine roughness values flutsk(cyl) are compared to an accompanying threshold luar . The threshold is calculated from a load- and speed dependent offset value, which is added to the lowest flutsk value per working cycle. If flutsk exceeds the threshold, misfire is detected.

Scheme 124

2.9 Connection of misfire detection methods (%DMDLAD)

If at least one method has detected a misfire event the information is provided to the function %DMDMIL.

2.10 Fault handling and misfire statistics (%DMDMIL)

Each combustion, apart from those deactivated, has to be checked for misfire since misfires can be distributed arbitrarily (Scheme 125) A fault handling action will, however, only take place if specific percentage misfire levels are exceeded.

The different effects of misfire (emission impairment and catalyst damage) are handled separately in two branches of the function.

During the fault entry a distinction is made as to whether it is an emissions relevant fault after start, during the driving cycle, or whether it is a catalyst damaging fault. Furthermore a cylinder identification of the misfiring cylinder is performed. At catalyst damaging misfire rates it is possible to switch off the injection of the corresponding cylinder to protect the catalyst. If more than one cylinder is misfiring, both the cylinder-individual fault entry and a "multiple misfiring" entry will be carried out (Scheme 126)

Any pending fault code is erased when monitoring in the next driving cycle encounters similar conditions without detecting a malfunction.

Scheme 125

2.10.1 Emissions Relevant Misfires

Emissions relevant fault handling is done by utilizing cylinder specific counters (fzabgzyl_0.... fzabgzyl_3 (Scheme 125)) that are incriminated each time a misfire is counted for the associated cylinder. The total sum of all misfires within every 1000 crankshaft revolutions is continuously tracked with another counter fzabgs. A reset of all counters is performed at the end of every 1000 crankshaft revolutions (CSR). Each cylinder is identified that individually has more than 10% of all detected misfires.

2.10.1.1 Emissions Relevant Misfires after engine start

A fault is set if the sum of all misfires exceeds a calibrated threshold within the first interval after engine startup. The corresponding fault code entry and appropriate MIL action will be performed (Scheme 126)

2.10.1.2 Emissions Relevant Misfires during driving cycle

If the sum of all misfires per 1000 CSR-interval (beginning with the second interval after start) exceeds a calibrated threshold for at least 4 times during the driving cycle, the corresponding fault code entry will be carried out (Scheme 126)

2.10.2 Catalyst Damaging Misfires

A rapid response to misfires that could potentially damage the catalyst is necessary. The monitoring interval here ( (Scheme 125)) is equivalent to 200 CSR. Analogous to emissions relevant misfires, cylinder specific counters fzkatzyl_0... fzkatzyl_3 and the sums total counter fzkats are used (Scheme 125)and (Scheme 126) to detect catalyst damaging misfires.

At each misfire event the sum counter is incriminated depending on a load and engine speed dependent weighting factor.

In order to protect the catalyst fuel injection will be shut off immediately at cylinders that are responsible for or contribute to a catalyst damaging misfiring rate. If more than one cylinder is misfiring, both the cylinder-individual fault entry and a "multiple misfiring" entry will be carried out (Scheme 126) Each cylinder that individually has more than 1/4 of all detected misfires is identified.

Scheme 126

4.1 Rough Leak Check

The air pump's motor current is monitored over a calibrated period of time while air is continuously pumped into the tank.

If the motor current exceeds a calibrated threshold value after the calibrated period of time, it implies no rough leak (> 0.04 in) is present in the evaporative system.

If the motor current is less than the calibrated threshold value a second confirmation check is performed utilizing a longer measurement so a more reliable result can be obtained.

4.2 Small Leak Check

The small leak check is performed if and only if the rough leak check has been performed and no rough leak was detected.

If the enable conditions for the small leak check (> 0.02 in) are fulfilled, the pump's motor remains in the active state (monitoring mode) until its current exceeds the reference current, or the motor current gradient is close to zero (current stabilizes below the reference current). If the motor current exceeds the reference current, the evaporative system is considered as tight. A small leak is assumed only if a second small leak check confirms a current stabilization below the reference current.

If the motor's current decreases during one of the checks, the check is aborted. If the number of subsequent unsteady current events exceeds a calibrated value the fault code "module error" is set.

(Scheme 127) shows typical pump motor current characteristics

Scheme 127

4.3 In-use Monitor Performance Ratio (IUMPR)

The incriminating of the numerator, the denominator, and the IUMPR calculation for the evaporative system diagnostic is executed by the IUMPR kernel function. The evaporative system diagnostic tracks and reports the 0.02 inch leak detection to the IUMPR kernel function via status flags.

5.1 Electrical check

The Signal lines of both Fuel level sensors are checked for electrical faults. Depending on the measured resistance an error FSTEmin or FSTEmax (Sensor 1) or FSTESmin or FSTESmax (Sensor 2) is set.

5.2 CAN Signal check

If the fuel level message received via CAN bus is corrupt or missing, a malfunction is detected and a signal fault FSTEsig (Sensor 1) or FSTESsig (Sensor 2) is set.

5.3 Range check

The physical range of the fuel level signal is between zero and the fuel tank size.

If the measured fuel level exceeds the valid fuel tank size for a calibrated period of time, a malfunction is detected and a fault FSTRmin is set (Scheme 128)

The minimum fuel level (zero) is a valid fuel level and can therefore not be checked

5.4 Plausibility check

The plausibility check of the fuel level sensor is based on the comparison of the calculated fuel consumption during driving to the measured fuel level change. If the deviation exceeds a calibrated threshold twice without healing the error condition is fulfilled.

To get a reliable O.K.-result the function has to wait for a significant change in either the measured or the calculated fuel level. This procedure can expire over several consecutive driving cycles (O.K.-Check (Scheme 129)). A faulty sensor can be detected faster. However, to get a reliable result the function has to wait until a certain deviation is reached. This procedure can expire over several driving cycles, as well (Fault detection (Scheme 130)).

In order to give a hint to the rootcause of the fault a further error distinction is performed

If the error condition is fulfilled and the measured fuel level change is below a calibrated threshold, a stuck fuel level sensor is supposed and a fault FSTRmax is set.

If the error condition is fulfilled and the measured fuel level change is above or equal to the calibrated threshold (fuel level sensor is not stuck) a plausibility fault FSTRnpl is set.

The procedure is reset if refueling or de-fueling is detected or if a check result was achieved (O.K. or fault).

Scheme 128

Scheme 129

Scheme 130

6.1 Plausibility check

For the plausibility check of the mass air flow signal, the quotient of the modeled mass air flow and the measured mass air flow is formed and filtered. If this filtered value lies below a calibrated threshold for a calibrated period of time, a HFMPLMin fault will be set. Likewise, if the value exceeds a calibrated threshold for a calibrated period of time, a HFMPLMax fault will be set.

7.1 Circuit continuity check

To detect a circuit continuity malfunction the period duration of the mass airflow signal is compared with an upper and a lower calibration limit to identify an intermitted contact. A short circuit is identified with a period duration equal to zero.

If the period duration of the mass airflow signal from the MAF sensor equals zero for a calibrated period of time, a short circuit is detected and a HFMEsig fault is set.

If the period duration of the mass airflow signal from the MAF sensor lies below the lower calibration limit for a calibrated period of time, an intermitted contact (high frequency) is detected and a HFMEmin fault is set.

If the period duration of the mass airflow signal from the MAF sensor exceeds the upper calibration limit for a calibrated period of time, an intermitted contact (low frequency) is detected and a HFMEmax fault is set.

7.2 Temperature compensation signal check

The built-in MAF sensor includes additionally a temperature compensation signal (drift compensation).

This signal must lie within a valid range during all engine conditions.

If the period duration of the temperature compensation signal from the MAF sensor lies below the lower calibration limit for a calibrated period of time, a KHFMEmin fault is set.

If the period duration of the temperature compensation signal from the MAF sensor exceeds the upper calibration limit for a calibrated period of time, a KHFMEmax fault is set.

7.3 Range check

The mass airflow must lie within a valid range during all engine operating conditions. A malfunction is detected and a HFMRmin or HFMRmax fault is set when the mass airflow respectively falls below or exceeds a calibrated minimum or maximum for a calibrated period of time.

8.1 Fuel injection calculation

In the powertrain control module the injection time (ti) is calculated from an engine load signal (rl) provided by the mass airflow sensor, an additive correction of the fuel trim adaptation (rka), a multiplicative correction of the fuel trim adaptation (fra) and a multiplicative correction from the fuel control system (fr) (Scheme 131)

8.2 Fuel trim adaptation

The fuel trim adaptation has 2 self-learning integrators, which all depend on engine speed and engine load (rkat, frau). The engine speed and engine load operating areas for rkat frau are (Scheme 114)

Depending on the enable condition for each integrator, the deviation of the fuel control system from its stoichiometric A/F ratio is "learned".

Scheme 131

Scheme 132

8.3.1 Near empty fuel tank functionality

A near empty fuel tank can cause air bubbles in the fuel delivery system and thus causes a lean A/F ratio. First the lambda controller and then the fuel trim adaptation tries to compensate. This can cause erroneous MIL illumination, because the fuel trim adaptation factor goes over a diagnostic threshold.

The following flowchart shows the functionality to ensure MIL illumination if the fault is correct and to avoid erroneous MIL illumination in case of a near empty fuel tank.

If one of the adaptation factors exceeds its diagnostic threshold, and the fuel tank is detected as being near empty, setting of the error is delayed for a certain time (depends on engine intake air mass).

Simultaneously, integration of the engine intake air mass begins.

If the integrated engine intake air mass (as a measure for fuel consumption) exceeds a calibrated threshold and the fuel trim adaptation factor still exceeds its threshold, the result of the fuel system monitoring is valid and the fault is set.

If the adaptation factor decreases under its diagnostic threshold before the integrated engine intake air mass exceeds its threshold, there is no fault detection. The integrated engine intake air mass value is stored for later refueling detection.

Refueling detection is started, as soon as the adaptation factor returned into its valid range. Refueling is detected, if the intake air mass, that is then integrated, exceeds a calibrated threshold (current integrated value minus stored value exceeds threshold).

9.2 Temperature check of the galvanic cell after engine start

The oxygen sensor's ceramic temperature is determined by measuring the internal resistance of its galvanic cell. A HSVnpl fault will be set if after start of heating the ceramic temperature of the sensor doesn't reach a calibrated minimum after a calibrated period of time.

9.3 Maximum heater output check

If the targeted temperature of the oxygen sensor's ceramic isn't reached during controlled operation, the duty cycle factor of the output function will converge towards one. A duty cycle factor equal to one for a long period of time is implausible and prohibited. A HSVmax fault is set when maximum heater output doesn't achieve the targeted temperature of the oxygen sensor's ceramic within a calibrated period of time.

10 Rationality check of the front oxygen sensor

(P2097, P2096, P2195, P2196)

This diagnostic function continuously checks the front oxygen sensor's response signal by comparing it with that of the rear oxygen sensor or by utilizing technical parameters of the engine control system. A faulty sensor signal is implied when the characteristic lambda curve derived from the front oxygen sensor's response signal ( (Scheme 133)below) indicates an air-fuel mixture that is leaner or richer than that expected from the nominal curve.

Four types of faults can be detected

Scheme 133

1. The integral component of the secondary lambda controller is interpreted as an offset in the characteristic curve of the front oxygen sensor. A shift is acceptable (because of tolerances) only when it lies between a calibrated minimum and maximum threshold value. An offset diagnostic via the lambda controller function detects a maximum fault PLLSUmax (shift into leaner region) or a minimum fault PLLSUmin (shift into richer region) and
2. direct comparison of the front oxygen sensor's signal with that of the rear oxygen sensor can detect a plausibility fault PLLSUnpl (shift into leaner region) or a signal fault PLLSUsig (shift into richer region).

10.2.1 Method A1 - shift of characteristic lambda curve to leaner region

A plausibility fault PLLSUnpl is set when the method A1 monitoring conditions are simultaneously fulfilled and the rear and front oxygen sensors both indicate a plausible rich and plausible lean mixture respectively.

10.2.2 Method B1 - shift of characteristic lambda curve to leaner region

A plausibility fault PLLSUnpl is set if at operating points with a desired normalized A/F ratio = 1, the rear oxygen sensor indicates a plausible rich mixture when all the corresponding monitoring conditions are simultaneously fulfilled for a calibrated period of time i.e. for a period longer than the duration of the lambda control system.

10.2.3 Method A2 - shift of characteristic lambda curve to richer region

A signal fault PLLSUsig is set when all method A2 monitoring conditions are simultaneously fulfilled and the downstream and upstream HO2S both indicate a plausible lean and rich mixture respectively.

10.2.4 Method B2 -shift of characteristic lambda curve to richer region

A signal fault PLLSUsig is set if at operating points with a desired normalized A/F ratio = 1, the downstream HO2S indicates a plausible lean mixture when all the corresponding monitoring conditions are simultaneously fulfilled for a calibrated period of time i.e for a period longer than the duration of the lambda control system

10.3 In-Use Monitor Performance Ratio (IUMPR)

The incriminating of the numerator, the denominator and the ratio calculation for the rationality check of the front oxygen sensor is executed by the IUMPR kernel function. The front oxygen sensor's rationality check diagnostic reports to the IUMPR kernel function via status flags.

11 Front oxygen sensor's response rate monitor

(P0133)

Aging, contamination and improper heating of the front oxygen sensor slows down its response rate. This diagnostic function continuously monitors the front oxygen sensor's response rate by performing an amplitude check.

During air-fuel mixture control, a rectangular signal of a defined amplitude and period is superimposed on the targeted air-fuel ratio (lambda) signal. The maximum and minimum of the modeled target lambda signal at the oxygen sensor's location is compared (within each period of the rectangular signal) with the corresponding maximum and minimum of the measured and filtered signal from the oxygen sensor.

Scheme 134

The mean value of the periodic ratios is recursively computed with a low-pass digital filter. It should be noted that the number of periodic ratios must be greater than a calibrated minimum. The output of the low-pass digital filter is a measure of the quality of the oxygen sensor's response rate.

A DFC_DYLSU min fault is set when the number of valid measurements exceeds a calibrated minimum and the output of the filter lies below a calibrated threshold.

Scheme 135

11.1 In-use monitor performance ratio (IUMPR)

The incriminating of the numerator, the denominator and the ratio calculation for the front oxygen sensor's response rate monitor is executed by the IUMPR kernel function. Like all monitors for which a standardized track and report in-use performance is required, the front oxygen sensor's response rate monitor reports to the IUMPR kernel function via status flags.

12 Electrical faults of the front oxygen sensor

(P0130)

Lambda control can be disabled only when at least a pending fault code (service $07) has been entered in the fault code memory. Several operating conditions do exist under which faulty components can be pinpointed only after a time delay. Lambda control must however be disabled when fault symptoms are detected.

This diagnostic function sets a general electrical fault LSVEmax. The actual fault which is accompanied by a second entry into the fault code memory is then pinpointed afterwards by the appropriate diagnostic function. This second fault entry could either be a sensor line error or a heater fault of the front oxygen sensor. In order to ensure timely MIL illumination, two-in-a-row principle, the general electrical fault is also set when a sensor line error or a heater fault of the front oxygen sensor is set. A general electrical fault of the upstream heated oxygen sensor will be set either

1. When the internal resistance of the oxygen sensor's galvanic cell is implausibly high or the ceramic temperature of the front oxygen sensor is implausibly low.

13 Monitoring of the front oxygen sensor's voltage

(P2414)

This monitor performs a rationality check of the voltage VA of the output signal of the front oxygen sensor after amplification by the CJ125 integrated circuit - (Scheme 136) VA depends on the characteristics of the oxygen sensor and those of the peripheral circuitry of the CJ125 IC and is plausible only within the calibrated range of 0V...4.8V.

Scheme 136

Generally, at a nearly stoichiometric air-fuel ratio ( lambda = 1.0) the output voltage will be clearly below the voltage read when the front oxygen sensor lies in air - (Scheme 136) A fault could be triggered if an electrically connected oxygen sensor is not properly mounted (or is not mounted at all) in the exhaust system. A fault is however set only after the state of the fuel tank has been validated. If the fuel tank were empty or its state unknown, it will be set only after 600 seconds have elapsed. This delay time validates the fact that even when in trailing throttle mode, the engine cannot run for another 600 seconds on an empty tank. A rationality fault ULSUnpl will be set when, given all monitoring conditions are fulfilled, the voltage of the front oxygen sensor VA lies below the maximum calibrated measurable limit but above the calibrated value which the sensor indicates when it lies in the air.

13.1 In-use monitor performance ratio (IUMPR)

The incriminating of the numerator and the denominator, the IUMPR ratio calculation, the determination of the monitor with the minimum IUMPR ratio in the oxygen sensor group (which has multiple monitors) and the preparation of the numerator and denominator of the front oxygen sensor's voltage monitor for Service $09 is executed by the IUMPR kernel function. Like all monitors for which a standardized track and report in-use monitor performance is required, the monitor of the front oxygen sensor's voltage reports to the IUMPR kernel function via status flags.

14.1 Open circuit - VM line interruption

The pump current of the galvanic (or Nernst) cell no longer flows when there is a VM line interruption. This leads to an extremely high resistance that persists even when the oxygen sensor is sufficiently hot. The oxygen sensor's ceramic temperature doesn't rise although the system reacts by increasing the heating power. A signal fault LSUVMsig will be set when the internal resistance of the galvanic cell remains irrationally high for a calibrated period of time.

14.2 Open circuit - UN line interruption

A UN line interruption leads to an irrationally high U R signal as well as an undefined output voltage U A . A signal fault LSUUNsig is set when the offset corrected voltage of the front oxygen sensor lies above the upper (or below the lower) plausible output voltage U A of the CJ125 IC required for detecting a UN line interruption.

14.3 Open circuit - IA line interruption

An IA line interruption leads to an implausibly large front oxygen sensor voltage during fuel cut-off operation. A signal fault LSUIAsig is set after a calibrated delay time, if the oxygen sensor's voltage is greater than or equal to a calibrated threshold. The fault is set after an additional calibrated time if the fuel tank is empty or in an unknown state.

14.4 Open circuit - IP line interruption

The pump current of the front oxygen sensor which flows through the IP line is equivalent to the oxygen concentration in the exhaust gas. An IP line interruption means the pump current will be permanently equal to zero. The output voltage UA of the CJ125 IC will remain constant i.e. it no longer varies with the oxygen concentration in the exhaust gas. An IP line interruption is detectable via three methods

1. detection during fuel cut-off
2. comparison with the set point A/F ratio of the front oxygen sensor
3. rationality check with the A/F mixture (lambda) control factor.

14.4.1 Detection during fuel cut off

A plausibility fault LSUIPnpl is set after a calibrated delay time when the value of the oxygen sensor's voltage lies below a calibrated threshold for a calibrated period of time during fuel cut-off.

14.4.2 Comparison with the set-point A/F ratio of the front oxygen sensor

A signal fault LSUIPsig is set when the set-point A/F ratio lies outside the calibrated stoichiometric operation range and the corresponding output voltage does however indicate stoichiometric operation.

14.4.3 Rationality check with the lambda controller factor

The change in the output of the lambda controller is observed from the moment the output voltage of the front oxygen sensor lies within the calibrated range that indicates a stoichiometric A/F ratio. A maximum fault LSUIPmax will be set when the output voltage stays within this calibrated range in spite of an ensuing lambda controller excursion that exceeds a calibrated threshold.

14.5 Short circuits to ground or to battery voltage

Short circuits are detected by a self diagnosis of the CJ125 IC. An integrated voltage comparator at each and every pin of the front oxygen sensor's CJ125 IC, detects and sets a maximum or a minimum fault if the voltage at that pin respectively lies above a calibrated maximum or below a calibrated minimum for a calibrated period of time.

14.6.1 Implausible commands counter

The CJ125 evaluation IC communicates with the main processor of the PCM via a serial port interface. They both transmit data to each other. Interference on the SPI bus leads to implausible signals. These implausible signals, which persist even when the data is re-transmitted, are tracked by incriminating an internal error counter. A signal fault ICLSUsig is set when the counter exceeds a calibrated threshold.

14.6.2 Comparison of initialization and mirror register

A further communication monitor compares the old value of the initialization register, which is backed up in a mirror register, with its current value after a rewrite. A plausibility fault ICLSUnpl is set after a calibrated period of time, if the current value of the initialization register isn't equal to that of its mirror register.

14.7 Low supply voltage of the CJ125 IC

The CJ125 IC is specified for supply voltages > 9V. It possesses a supply voltage detection module. Low supply voltages lead to faulty diagnosis at the voltage comparators. A minimum fault ICLSUmin is set when the supply voltage drops below 9V. The supply voltage monitor is aborted when the monitoring conditions are no longer fulfilled i.e. the battery's voltage is no longer greater than 10.7V.

14.8 Electrical trimming

Electrical trimming of the front oxygen sensor is performed in order to determine and store the difference between the expected and the actual pump-current-proportional output voltage. This difference stems from hardware tolerances. Electrical trimming is carried out once after engine start and once in the idle mode during a calibrated period of time. A maximum fault ICLSUmax is set after electrical trimming, when the adaptation value for the corresponding curve (normal and rich) exceeds a calibrated maximum.

15.1 Sensor wire interruption or damaged sensor heating element

A LSHsig fault, indicating a wire interruption of the sensor's signal or the sensor's ground or a damaged heating element of the sensor is set if the sensor's voltage remains within a calibrated range (i.e. the upper threshold for rich mixtures and the lower threshold for lean mixtures) for more than a calibrated period of time. A signal fault indicating a wire interruption of the sensor's ground is also set when the internal resistance of the rear oxygen sensor as well as the modeled exhaust gas temperature at the vicinity of the rear oxygen sensor exceed their calibrated thresholds.

Scheme 137

15.2 Short circuit to battery

A LSHmax fault that indicates a short circuit of the sensor's signal wire to the battery is set if the output voltage of the rear oxygen sensor permanently lies above a calibrated value for a calibrated period of time.

15.3 Wire to wire short circuits

A LSHmin fault that indicates a wire-to-wire short circuit between the sensor's signal and its ground or a short circuit between the sensor's signal and the car body's ground is set when the evaluation voltage stays below a calibrated threshold for a calibrated period of time with the oxygen sensor remaining cold after engine start.

16.1 Internal resistance of the rear oxygen sensor's galvanic cell

The diagnosis of the heating of the rear oxygen sensor runs continuously and is carried out by measuring the internal resistance of its galvanic cell and comparing it with calibrated typical temperature dependent values. A HSHnpl fault will be set after a calibrated delay time if the measured value of the internal resistance is greater than its expected setpoint value.

17 Aging monitor of the rear oxygen sensor

(P2270, P2271)

The aging monitor of the rear oxygen sensor consists of an oscillation check and a threshold check during fuel cut-off. The monitor runs continuously and employs the same procedure in both banks.

17.1 Oscillation check

During normal engine operation the normalized A/F ratio and hence the voltage of the rear oxygen sensor oscillates about the set point value. The oscillation check triggers a test function if the measured voltage of the oxygen sensor's signal permanently lies below or above the set point value for a calibrated period of time. The test function applies a rich A/F mixture if the voltage was below the set point value or a lean A/F mixture if it was above the set point value. If the resulting voltage doesn't cross the set point value in the expected direction after applying a lean or rich A/F mixture, a minimum LASHmin or maximum fault LASHmax will be set respectively.

17.2 Threshold check during fuel cut-off

A signal fault LASH is set when the rear oxygen sensor's voltage exceeds a calibrated threshold for a calibrated period of time during fuel cut-off.

18 Rear oxygen sensor's response rate monitor

(P013A, P013E)

The rear oxygen sensor's response rate is determined by observing its voltage behavior during fuel cut-off - (Scheme 138) The monitor commences at fuel cut-off only when the voltage of the rear oxygen sensor voltage reaches or exceeds a calibrated rich A/F maximum at a time when all the necessary monitoring conditions are fulfilled. We define a response time (tr) as the time taken for the rear oxygen sensor's voltage to fall to a calibrated lean A/F ratio minimum from the point when the diagnosis is enabled. We further define a transient time (tt) as the time taken for the rear oxygen sensor's voltage to drop from a relatively higher to a lower calibrated voltage as depicted in (Scheme 138).

Scheme 138

Both the response and the transient times are fed into their corresponding statistic filters. A valid diagnostic result does exist only when a calibrated number of valid response time measurements and a calibrated number of valid transient time measurements have been achieved. A maximum fault DYLSHmax is set when statistical value for the transient time exceeds a calibration. A signal fault DYLSHsig will be set when the statistical value for the response time exceeds a calibration.

20 Idle speed control (ISC)

(P1562; P1561; P0507; P0506)

The diagnosis of the idle speed control (ISC) is split into a diagnosis during cold start and a diagnosis during warm operation. Both diagnoses work the same way with slight differences in threshold limits, debouncing time and monitoring conditions.

21 Throttle position sensors

(P0123, P0122, P0223, P0222; P0120, P115F)

The diagnosis of the two throttle position sensors used for measuring throttle angle consists of a range check and a rationality check of their measured voltages.

21.1 Range check

The range check is performed by measuring the voltages of both sensors and comparing them with their respective minimum and maximum calibrated values.

If the measured voltage exceeds the calibrated maximum, a malfunction is detected and a DK1Pmax fault (sensor 1) or DK2Pmax fault (sensor 2) will be set.

If the measured voltage lies below the calibrated minimum, a malfunction is detected and a DK1Pmin fault (sensor 1) or DK2Pmin fault (sensor 2) will be set.

21.2 Rationality check

The rationality check uses the measured voltages of sensor 1 and 2 to calculate the corresponding throttle position angles.

A rationality fault DKPUPnpl is also set when the difference between the throttle angles of both sensors exceeds a maximum calibrated threshold value for a calibrated period of time. Only if the difference between both sensors exceeds a second threshold the system will be placed in "first DK- limp home mode" (throttle to maximum and load controlling with valve lift).

Rationality faults will be set to the sum fault path DKnpl, too, if

1. the deviation between the calculated throttle position angle and the measured throttle position angle exceeds a calibrated threshold for a calibrated period of time.
2. The system will then be placed in limp-home mode or
3. the digital controller (DLR) correction range is at limit. This occurs if the PWM duty cycle output of the digital position controller (DLR) exceeds an upper calibration or is lower than a calibration value for a long period of time.
4. The system will then be placed in limp-home mode or
5. a DKPUPnpl fault is set.
6. both sensor errors, including signal range errors, also lead to a fault code entry DKnpl

22.1 Return spring check

The time required by the return spring to bring the wide open throttle valve to its mechanical default position is measured and compared with a calibrated threshold value.

If the expected mechanical default position is not reached within a calibrated time after switching off the power stage, a DVEFmax fault indicating a malfunction will be set.

If the desired start position (open throttle valve) for the actual return spring check is not reached within a calibrated time, a DVEFmin fault indicating malfunction will be set.

22.2 Lower mechanical throttle stop check during the first initialization

If during the first initialization of the control unit the throttle body adaptation cannot be performed (lower mechanical limit is out of range), "Lower mechanical limit implausible" is detected, the system runs in the "irreversible safety fuel cut off" state and a plausibility fault DVEU is set.

23 Throttle control unit

(P2103, P2102, P061F, P2100; P1637; P1639; P1638)

The purpose of the function is to control the throttle actuator and to diagnose faults in the control loop. The position of the throttle valve is determined by a digital controller (DLR) which sends a pulse width modulated (PWM) signal, along with a flag that indicates the direction of rotation, to the throttle valve's power stage. The DV-E power stage is designed as an integrated H-bridge with internal current limitation.

Scheme 139

23.1 Throttle valve power stage check

The actual electrical diagnosis of the throttle valve power stage is executed with the built-in controller hardware and the results are stored as error flags in a dedicated status register.

The check of these error flags is only performed if either a DVELnpl fault (and therefore an impact on the controllability of the throttle valve) is detected.

In case of

1. the corresponding DVEEmax fault is set when an error flag for 'short circuit' is set
2. the corresponding DVEEmin fault is set when the error flag for 'over-heating' or 'over-current' is set
3. the corresponding DVEEnpl fault is set when an error flag for 'SPI bus or signal fault' is set
4. the corresponding DVEEsig fault is set when the error flag for 'open load' is set.

23.2 Non-permissible deviations between requested and actual throttle position

Throttle position is monitored for non-permissible deviations. If the deviation between the set point and the actual throttle valve position exceeds a calibrated value for a calibrated period of time a rationality fault DVELnpl will be set. The system will then be placed in limp-home mode.

23.3 Duty cycle range check

If the PWM duty cycle output of the digital position controller (DLR) exceeds an upper calibration or is lower than a calibration value for a long period of time 2, a duty cycle malfunction and actuator current malfunction respectively is detected. The system is set to "Throttle valve drive default function" state and a DVERmax fault is set. The system will then be placed in limp-home mode.

If the DLR output surpasses the duty cycle limits only for a shorter period of time 1, for safety reasons the system requests a fuel deactivation for a short time and a DVERmin fault is set. The system will then be placed in limp-home mode.

24.1 Circuit continuity checks

The circuit continuity check compares the measured engine coolant temperature with an upper and a lower threshold to detect out-of-range values.

If the coolant temperature signal exceeds the calibrated upper threshold for a calibrated period of time, a TMEmax fault will be set.

If the coolant temperature signal lies below the calibrated lower threshold for a calibrated period of time, a TMEmin fault is set.

24.2 Rationality checks

To determine the rationality of the ECT sensor several checks are performed.

The low side check calculates a reference engine coolant temperature with help of a temperature model. This calculated temperature is reduced by a calibrated safety margin and compared with the actual measured engine coolant temperature.

If the measured engine coolant temperature lies below the calculated and reduced temperature for a calibrated period of time, a TMPmin fault will be set.

The stuck check monitors the rise and drop behavior of the coolant temperature during a change in engine operation conditions.

If the engine coolant temperature change lies below a calibrated threshold for a calibrated number of driving condition changes (rise and drop) all for a calibrated period of time, a TMPnpl fault will be set.

25.1 Circuit continuity check

The circuit continuity check compares the measured intake air temperature with an upper and a lower calibration limit to detect out-of-range values.

If the intake air temperature signal exceeds the upper calibration limit for a calibrated period of time (e.g. caused by a short circuit to ground), a TAEmax fault will be set.

If the intake air temperature signal lies below the lower calibration limit for a calibrated period of time (e.g. caused by a short circuit to supply voltage or wire interruption), a TAEmin fault will be set.

25.2 Rationality checks

To determine, whether the intake air temperature is rational, several checks are performed.

25.2.1 Low side check

The low side check monitors the difference between the engine coolant temperature and the intake air temperature when the engine is cooled down. For a cooled down engine both temperatures must be nearly equal for a short time after start.

If the difference between intake air temperature and engine coolant temperature exceeds a calibrated threshold for a calibrated period of time, a TACSmin fault will be set.

25.2.2 High side check

The high side check monitors, depending on mass airflow and vehicle speed, whether the measured intake air temperature exceeds a maximum threshold.

If the intake air temperature exceeds or is equal to a calibrated threshold while the monitoring conditions are fulfilled, a TARmax fault will be set.

25.2.3 Fix check

The fix check monitors the rise and drop behavior of the intake air temperature under defined driving conditions.

If the monitoring conditions are fulfilled and the difference between the maximum and minimum value lies below a calibrated threshold, a TARnpl fault will be set.

26 Ambient air temperature sensor

(P0073, P0072; P110F; P0071, P0071)

The diagnosis of the ambient air temperature sensor consists of a range check, a model based rationality check and a cold start rationality check of the temperature signal that the ECU receives via the CAN bus. The cold start rationality check is only performed after a cold start is detected and the model based rationality check is always executed if the monitoring conditions are fulfilled. Both tests mentioned above results in the same error path. The CAN signal itself is also checked.

26.1 CAN Signal Check

If the ambient air temperature received via CAN is not valid for a calibrated period of time, a TUMEsig fault indicating a malfunction will be set.

26.2 Range Check

A TUMEmax fault, indicating a short circuit to battery voltage or a broken wire, and a TUMEmin fault, indicating a short circuit to ground, is set, if the ambient air temperature sensor supplies the respective error conditions about the CAN Data Bus to the ECU.

26.3 Model based Rationality Check

A model based rationality check of the temperature signal that the ECU receives via the CAN bus is performed by comparing it with the ambient air temperature that is modeled as indicated in (Scheme 140).

Scheme 140

A TUMPnpl fault is set when the difference (positive) between the measured and the modeled ambient air temperature exceeds a calibrated threshold for a calibrated time.

A TUMPsig fault is set when the difference (negative) between the measured and the modeled ambient air temperature lies below a calibrated threshold for a calibrated time.

26.4 Cold start Rationality Check

A cold start rationality check of the temperature signal that the ECU receives via the CAN bus is performed by comparing it with the intake air temperature.

A plausibility fault TUMP is set when the difference (positive) between the measured ambient-and the intake air temperature exceeds a upper calibrated threshold.

A signal fault TUMP is set when the difference (positive) between the measured ambient-and the intake air temperature exceeds a lower calibrated threshold.

27.1 Circuit continuity check

The circuit continuity check compares the sensor signal voltage with an upper and lower limit to detect short circuits.

If the measured value from the atmospheric pressure sensor exceeds the upper calibration limit for a calibrated period of time, a short circuit to battery is detected and a PUEmax fault will be set.

If the measured value from the atmospheric pressure sensor lies below the lower calibration limit for a calibrated period of time, a short circuit to ground is detected and a PUEmin fault will be set.

27.2 Range check

Taking into account the lowest and highest driveable altitude the pressure must lie within a valid range during all conditions.

If the measured value from the atmospheric pressure sensor lies below the valid minimum pressure for a calibrated period of time, a malfunction is detected and a minimum fault PUR is set.

If the measured value from the atmospheric pressure sensor exceeds the valid maximum pressure for a calibrated period of time, a malfunction is detected and a maximum fault PUR is set.

27.3 Rationality check

The first rationality check compares, during the current driving cycle, the change of the atmospheric pressure within a calibrated period of time. Under normal driving conditions e.g uphill driving this change should be very slow.

If the absolute change of the measured pressure within a calibrated period of time exceeds a calibrated threshold for a calibrated period of time, a malfunction is detected and a signal fault PUR is set.

The second rationality check compares, during ignition on and engine off, the measured atmospheric pressure with the stored atmospheric pressure of the last driving cycle. After normal parking conditions (engine off) the difference between these two values should be very small. To cover special circumstances e.g. transportation from low to high altitude the measured atmospheric pressure may additionally be compared, after start of engine, with a modeled atmospheric pressure based on the mass airflow sensor. This additional check is only done if the signal change since the last driving cycle exceeds the threshold.

If

1. the absolute difference between the measured and stored atmospheric pressure exceeds a calibrated threshold (during ignition on and engine off) and
2. the absolute difference between measured atmospheric pressure and modeled atmospheric pressure exceeds a calibrated threshold (during engine running)

28.1 Circuit continuity checks

The maximum voltage-reading from the pressure-differential sensor is compared with the calibrated maximum value. If the sensor's voltage exceeds a calibrated threshold for a calibrated period of time, a condition that is caused by short-circuit to battery, a DDSSMax fault will be set.

The minimum voltage-reading from the pressure-differential sensor is compared with the calibrated minimum value. If the sensor's voltage lies below a calibrated threshold for a calibrated period of time, a condition that is caused by short-circuit to ground or due to wire interruption, a DDSSMin fault will be set.

28.3 Range check

The value of the pressure control outlet is checked if it is within a calibrated range. If the measured value exceeds a calibrated threshold for a calibrated period of time, a DPSRPLMax fault will be set. Otherwise, if the measured value lies below a calibrated threshold for a calibrated period of time, a DPSRPLMin fault will be set.

29.1 Range check

Any engine design specifications do result in a maximum drivable vehicle speed that cannot be exceeded. A maximum fault VFZEmax will therefore be set when the determined vehicle speed at any instance exceeds the calibrated possible maximum for a calibrated period of time.

29.2 Stuck check

A minimum fault VFZEmin is set when the vehicle speed stays constant for a calibrated period of time.

29.3 Rationality check during fuel cut-off

If the fuel cut-off condition is set for more than a calibrated period of time it implies the vehicle must be in motion. Hence a minimum fault VFZNPmin will be set if the vehicle speed lies below a calibrated minimum.

29.4 Rationality check via evaluation of the engine speed to vehicle speed ratio

The engine speed to vehicle speed ratio depends on the selected gear and will lie within a defined range at steady engine loads. A rationality fault VFZNPnpl indicating an implausible vehicle speed signal is set when the calculated engine to vehicle speed ratio lies beyond the defined ratio range for the currently engaged gear.

Scheme 141

30.1 CAN timer signal check

If the timer message (received via CAN bus) is corrupt or missing for a calibrated period of time, a CUHRsig fault will be set.

30.2 Rationality Check

The PCM measures and analyses the received 'free running timer' during a calibrated monitoring period with help of an internal clocked reference timer. So the deviation of synchronism per defined monitoring period is analyzed. The diagnosis is retriggered after expiration of the monitoring time period and starts with resynchronizing of the internal clocked reference timer with the externally clocked free running timer.

If, during the monitoring period, the absolute time difference between the internal reference timer and the external free running timer exceeds a calibrated threshold for a calibrated period of time, a CUHRnpl fault will be set.

31.1 Functional Principle

An engine speed sensor that employs either the Hall effect or another induction principle is mounted, separated by a narrow air gap, directly opposite the rim of a 60 less 2 teeth ferromagnetic wheel attached to the crankshaft. The large tooth gap (the missing 2 teeth) in the rotating wheel's signal is assigned to a defined crankshaft position and serves as a reference mark for synchronizing the powertrain control unit - (Scheme 142)

One complete working cycle of a four-stroke engine comprises two crankshaft revolutions i.e. 720°. The power train control unit utilizes a second signal to determine if the cylinder is in the compression or exhaust phase. This second signal is delivered by an inductive sensor mounted directly opposite the rim of another toothed wheel attached to the camshaft.

Engine speed sensor (crankshaft) signal

Scheme 142

Up to four camshaft position sensors can be analyzed, each with his own fault path. In case of a system with more than one camshaft position sensor, each sensor is monitored separately but all in the same way.

31.2 Detection of a crankshaft signal failure

With the help of the camshaft position sensor signal it is possible to detect a loss of the crankshaft signal. While the crankshaft signal is not detectable, the number of camshaft edges are counted. If the counter exceeds a calibrated threshold, a EpmCrSNoSig fault will be set.

31.3 Detection of a disturbed crankshaft signal

A disturbed crankshaft signal is detected if plausibilisation of the signal detection is not working.

The number of plausibilisation errors is counted and incremented by a calibrated value for every plausibility fault. If the counter reaches a calibrated threshold, a EpmCrSErrSig fault will be set.

33.1 Functional Principle

An engine speed sensor that employs either the Hall effect or another induction principle is mounted, separated by a narrow air gap, directly opposite the rim of a 60 less 2 teeth ferromagnetic wheel attached to the crankshaft. The large tooth gap (the missing 2 teeth) in the rotating wheel's signal is assigned to a defined crankshaft position and serves as a reference mark for synchronizing the powertrain control unit - (Scheme 143)

One complete working cycle of a four-stroke engine comprises two crankshaft revolutions i.e. 720°. The power train control unit utilizes a second signal to determine if the cylinder is in the compression or exhaust phase. This second signal is delivered by an inductive sensor mounted directly opposite the rim of another toothed wheel attached to the camshaft.

Engine speed sensor (crankshaft) signal

Scheme 143

Up to four camshaft position sensors can be analyzed, each with his own fault path. In case of a system with more than one camshaft position sensor, each sensor is monitored separately but all in the same way.

33.2 Detection of the camshaft signal failure

This check detects a loss of the camshaft signal. A counter adds all the crankshaft edges since the last interrupt. As soon as one or more camshaft edges acquire, the counter is reset. If the counter reaches a calibrated threshold, the level of the signal will be checked. At a high level, a EpmCaSI1NoSigMax fault will be set. Or at a low level a EpmCaSI1NoSigMin fault will be set.

33.3 Detection of a disturbed camshaft signal

During a synchronized state the number of camshaft edges will be checked. If the number of camshaft edges is not plausible or if the engine is not in a synchronized state, a pattern matching check of the camshaft signal will be performed. As soon as the debounce counter exceeds a calibrated threshold, a EpmCaSI1ErrSig fault will be set.

34 Variable camshaft timing (VANOS)

(P0016, P0017, P0011, P0012, P0014, P0015)

The BMW-Vanos is a combined hydraulic and mechanical camshaft control unit, managed by the ECU. The double Vanos allows the engine to control valve timing continuously for both intake and exhaust camshafts. The electronically control of the Vanos positions is dependant on engine speed, load and temperature.

The function DEAVANOS is monitoring the correct mechanical function of the variable camshaft timing. The diagnosis carries out a continuous rationality check of the Vanos function.

If a malfunction is detected, an error bit will be set and sent to the module LAY_DFC where the error is debounced and the setting of the corresponding DTC is triggered.

Two parameters are monitored for all camshafts, i.e. the adapted reference position and the control deviation. The diagnostic strategy for inlet and exhaust camshaft is identical

34.1 Vanos end position in range

This diagnosis checks whether the camshaft position is in an expected range during the Vanos unit is in its end position. If the camshaft position is out of this range, a min fault will be set.

34.2 Vanos reference position offset ("one tooth off")

This diagnosis detects a one-tooth error in camshaft to crankshaft alignment (e.g. by a slipped chain). If the adapted camshaft reference position exceeds an adjustable limit based on a previous adaptation value (one chain-tooth), a min fault is set.

34.3 Control deviation of the camshaft position controller (Target Error and Slow Response)

In this diagnosis the difference between the actual and target position of the Vanos units ("control deviation") is checked. If the calculated difference between these two positions exceeds an adjustable threshold, a counter is started. The counter is incremented twice per crank revolution (but not exceeding 10 msec-rate).

If the counter exceeds a limit (also adjustable), a fault is set.

The control deviation diagnosis, the end position in range diagnosis and the one tooth off diagnosis have got an interface to the "In-use monitoring performance ratio" function.

34.4 In-use monitor performance ratio (IUMPR)

The incriminating of the numerator, denominator, and the ratio calculation for the Variable Camshaft Timing monitor is executed by the IUMPR kernel function. Like all monitors for which a standardized track and report in-use performance is required, the Variable Camshaft Timing monitor reports to the IUMPR kernel function via status flags.

35.1 Electrical check

In this diagnosis every single line of the knock sensor is checked for a short circuit. If the difference between the measured voltage of the knock sensor and a reference voltage lies below a minimum calibrated threshold, a KnDetSens1PortA/BMin fault will be set. If it exceeds a maximum calibrated threshold, a KnDetSens1PortA/BMax fault will be set.

38 Valvetronic

(P1047, P1048, P1049, P1050, P105C, P1056, P1057, P1031, P1019, P1020, P1062, P1063, P1030)

Scheme 144

40.1 Range check

The range check compares the measured system voltage with an upper calibration limit to detect out-of-range values.

If the measured system voltage exceeds the upper calibration limit for a calibrated period of time, a UBRmax fault will be set.

43 Communication between the micro-controller and the monitoring module

(P163E)

This function implements the query-response communication between the function controller (FC) and the monitoring module (MM). In contrast the MM provides different queries which are answered with the appropriate responses by the FC.

A fault MoCComctErrMM will be set when the monitoring module is diagnosed as defective for several consecutive number of times.

45.1 Automatic Transmission

The diagnosis of the powertrain CAN communication between the Transmission Control Module (TCM) and the Powertrain Control Module (PCM) is done by supervision of the received TCM powertrain CAN messages.

If the checksum of a TCM powertrain CAN message is wrong for a calibrated period of time, a malfunction is detected and a CEGSnpl fault will be set.

If a TCM powertrain CAN message is missing for a calibrated period of time, a timeout is detected and a CEGSsig fault will be set.

If the sequence number of a TCM powertrain CAN message is wrong for a calibrated period of time, a malfunction is detected and a CEGSmin fault will be set.

46.2 Check of the output stage

The Integrated Circuit CJ4x/9x checks the output signals of several components for basic circuit functionality.

The output stage of the PCM is first checked. Depending on this output stage, the signal levels are then monitored by using a test algorithm.

The test algorithm contains several tests measuring current and voltage of the output stages. The output stage conditions turn off (high) and turn on (low) must be reached once. In case of fault detection in one condition the fault is verified. A test to detect a short circuit to battery (set max fault) is called a "low test". It can be performed only while the output stage is conducted. A test to detect a short circuit to ground (set min fault) or a wire interruption/break (set signal fault) is called a "high test". The "high test" algorithm can detect both distinctively. It can be performed only while the output stage is not conducted.

The diagnosis of the output stage IC CJ4x/9x of the engine PCM is the basic functionality for the electrical monitoring of circuit continuity of the following components

1. canister Purge valve
2. thermostat
3. powerstage of injector valve
4. variable camshaft control (inlet and outlet)
5. variable valve timing control unit
6. heater of oxygen sensor downstream catalyst
7. evaporation System Pump Motor (for diagnosis)
8. heater of oxygen sensor upstream catalyst

47 Cold start emission reduction strategy

The cold start emission reduction strategy comprises a network of individual component diagnostics and engine functions. During cold start the key cold start control parameters (engine idle speed, variable valve timing and retarded ignition angle) are monitored or limited such that a malfunction will be detected if the vehicle's emissions exceed 150% of the applicable FTP standard. The retarded ignition angle limitation is calibrated for 100% of the applicable FTP standard.

47.1 Engine idle speed control (ISC)

A separate diagnosis of the engine idle speed is performed during cold start. A detailed description of this diagnosis can be found in the corresponding section of this documentation. The idle speed control diagnosis principally checks whether there is a permanent deviation between the current and the set point idle speed.

47.2 Variable valve timing

The standard diagnosis of the variable valve timing is performed during cold start. A detailed description of this diagnosis can be found in the corresponding section of this documentation.

The variable valve timing diagnosis checks if the camshaft is locked during engine start and whether the position and timing of the commanded valve timing has been achieved.

47.3 Limitation of advance of retarded ignition angle during catalyst heating

The powertrain control unit uses a control approach which is based on a torque structure. This torque structure converts the torque demand of the driver (accelerator pedal input) into an air charge and ignition based torque. During the catalyst heating phase, the ignition angle is retarded through a parameter described as ignition based torque reserve. In return, as compensation, the air charge based torque is increased to reach the desired overall torque. Instead of monitoring the ignition angle the ignition based torque reserve is limited to a necessary minimum which assures that a minimum level of retarded ignition angle is maintained. This minimum is calibrated such that the exhaust emission does not exceed 100% of the emission standard.

Scheme 145

47.4 In-Use monitor performance ratio (IUMPR)

Since there is no specific cold start emission reduction strategy diagnosis the necessary ratio is assured by the ratios of the relevant individual component diagnostics.

50 DME input/output listing

DME INPUT/OUTPUT LISTING

51 In-use monitor performance ratio-kernel function

The in-use monitor performance (IUMPR) kernel function represents the core of the software algorithms in the OBD II system implemented to individually track and report in-use monitor performance, in the standardized tracking and reporting format, for every monitor of the following components/systems (subsystems A...E)

1. A: catalyst
2. B: primary oxygen sensor
3. C: evaporative system (only 0.02 inch leak detection)
4. D: VVT system and
5. E: secondary air system (not implemented in this engine).

All monitors for which an in-use performance record is required do have an interface (a function identifier) through which they communicate with the IUMPR kernel function. It is this kernel function that does the actual tracking and preparation for reporting in the standardized format as depicted in (Scheme 146). The IUMPR kernel function additionally tracks and records the ignition cycle counter, the general denominator for every driving cycle and determines the monitor with the lowest numerical ratio within each group that has multiple monitors.

Scheme 146

51.1 Ignition cycle counter

The ignition cycle counter, when incremented, is incremented by an integer of one and only once per driving cycle. If the ignition cycle counter reaches the maximum value of 65,535, it rolls over and increments to zero on the next ignition cycle to avoid overflow problems.

51.2 General denominator

The general denominator, when incremented, is incremented by an integer of one and only once per driving cycle. If the general denominator reaches the maximum value of 65,535, it rolls over and increments to zero on the next driving cycle that meets the general denominator definition to avoid overflow problems.

51.3 IUMPR - Records

The kernel function maintains a record, a collection of elements from different types of arrays as depicted in (Scheme 147) below, for each monitor for which in-use performance ratio tracking is required. An update of a monitor's record is triggered or inhibited by the monitor itself. Each monitor's function identifier addresses its corresponding record via a pointer.

Each record holds the following information about the respective monitor

Scheme 147

Scheme 148

1. the function identifier (interface between monitor and IUMPR kernel function)
2. the associated diagnostic fault path
3. the numerator
4. the denominator
5. IUMPR status information from the diagnostic function
6. the associated component/system group (necessary for selection of minimum ratio of multiple monitors of one of the subsystems A...E).

51.4 Incrementing the numerator and denominator

A cyclic check is performed to find out if all conditions necessary for incriminating the numerator and the denominator have been fulfilled.

51.5 Minimum ratio selection (multiple monitors)

The associated component/system group identifier in a record is a pointer to the group (subsystem A...E) a monitor belongs to. IUMPR ratios are continuously calculated for all monitors. The IUMPR kernel function continuously determines the monitor with the lowest ratio in each group and provides its numerator and denominator values to Service $09 of the generic scan tool together with the ignition cycle counter and the general denominator.

Scheme 149

Scheme 150

The DLC is located at the lower left side of the instrument cluster (Scheme 151) Actually still open if there will be one cover with the letters "OBD" on it as shown removed in (Scheme 152) or no cover.

Scheme 151

Scheme 152

54 Calculated load and fuel trim determination

The calculated engine load "rl" is based on a calculated load signal balanced with the output signal delivered by the hot-film air-mass sensor (HFM).

It is calculated as follows

Scheme 153

mszyl: calculated load signal balanced with mshfm and corrected with mste

mshfm: air mass from HFM

mste: calculated gas mass flow through canister purge valve

nkw: engine speed

K_UFAK_MS_RF: constant depending on displacement

In case of a malfunction of the HFM the balancing with mshfm is cut off. Mszyl is calculated by the throttle valve angle, the variable valve timing, the residual exhaust gas and the engine speed.