Self Diagnosis - Theory & Operation (N52): Overview BMW X5 M E70 рестайлинг

1.1.1 Diagnostic overview

Catalyst monitoring is based on the monitoring of the o xygen s torage c apability (OSC) by comparing the signals of the O2 sensor upstream and downstream the catalyst.

The engine control stimulates the regular lambda oscillations of the exhaust gas. These oscillations are needed for best possible catalyst conversion. They are damped by the storage activity of the catalyst. The amplitude of the remaining lambda oscillations downstream the catalyst indicates the oxygen storage capability.

The efficiency of the catalyst system is tested during steady state driving by cycling the air fuel ratio LEAN and then RICH for a calibratable number of cycles while monitoring the OSC.

Prior to the catalyst test the canister purge valve is closed or opened with low canister purge value. This is to eliminate the influence of canister vapors on the downstream sensor during the test.

1.6.3.1 Monitoring overview

The diagnosis of the fuel level sensor signal consists of a circuit continuity check and a correlation check.

1.7.1.2.2 Monitoring description

This function determines, if an open circuit in any of the four electric lines (Reference Voltage, Virtual Ground, Pumping Current and Trim Current) is present in the w ide r ange a ir f uel (WRAF) sensor.

This function shall be triggered only if one of the following diagnosis is active (to set the readiness bit), which are ' UPSTREAM OXYGEN SENSOR - SIGNAL MONITORING DURING FUEL CUT-OFF ' and ' UPSTREAM OXYGEN SENSOR - HEATER MONITORING '. The function shall go to the state = "active" only if one of the diagnoses above detected a fault.

(Reference Voltage)

If a heater error exists and sensor voltage is too low, while the internal resistance measurement is turned off, an open circuit in the line reference voltage occurred.

(Virtual Ground) or (Pumping Current)

An open circuit in line virtual ground or in the line pumping current can be detected if the sensor signal stocks near lambda 1. The sensor non-activity can be detected by the Oxygen Sensor Signal Monitoring during fuel cut-off (signal voltage below e.g. 2.1 V) in fuel cut-off).

(Trim Current)

If the sensor shows an augmented gain, i.e. the sensor signal is higher than the nominal characteristic line, the plausibility test during the fuel cut-off phase shall detect this symptom (signal voltage above e.g. 5.6 V) during fuel cut-off) and an open circuit is assigned to the line trim current.

1.7.1.4.1 Monitoring description

The oxygen sensor signal activity check monitors if the sensor is attached to the exhaust pipe and whether the exhaust is sampled correctly (no leakage). A malfunction is detected if the oxygen sensor voltage is above a threshold (shows too lean mixture in part load or full load)

If the above mentioned malfunction is detected, the corresponding fault code is stored.

MONITORING FUNCTION CHART

1.7.1.5.1 Monitoring description

This function will detect if the Oxygen Sensor wire harness has been cross connected, i.e., Bank 1 with Bank 2. This is performed by the use of the output of the fuel correction (lambda controller) of each bank. If this control is on opposite limit at bank 1 and bank 2, the sensors are swapped and the corresponding fault code is stored.

Corresponding fault code

P0040

1.7.1.6.1 Monitoring description

This function shall deliver information indicating that the sensor characteristic line has a shift to lean (Characteristic Shift Down) or to rich, which shall be done by summarizing all similar failure symptoms of this kind.

In dependence of the shift strength there are three different paths followed by this diagnosis

1. Strong shift to lean/rich: If the lambda sensor upstream shows a rich signal while downstream lambda sensor signal is lean (or vice versa) and additionally the lambda controller goes to its limit, this error is recognized by the upstream sensor plausibility check.
2. Middle strong shift to lean/rich: If the trim controller goes to its limit but the lambda controller does not, the downstream oxygen sensor signal activity check (P114A, P114B, P114C, P114D) recognizes that the system has a problem and a failure code is stored. Referring to this failure entry, the «DOWNSTREAM ACTIVE TEST»(ref-361398-S07884824332010051400000) is triggered. It detects that the problem is in the upstream oxygen sensor, which is showing a characteristic line shift to lean or to rich. The appropriate DTC will be stored along with the downstream sensor signal activity check DTC.
3. Mild shift to lean/rich: The trim controller I-share goes to its limit but the lambda controller does not. The trim control plausibility monitoring (P2096, P2097, P2098, P2099) recognizes that the system has a problem and a failure code is stored. Referring to this failure entry, the «DOWNSTREAM ACTIVE TEST»(ref-361398-S07884824332010051400000) is triggered. It detects that the problem is in the upstream oxygen sensor, which is showing a characteristic line shift to lean or to rich. The appropriate DTC will be stored along with the fuel correction DTC.

1.7.1.9.1 Diagnostic overview

The purpose of this function is to detect oxygen sensor heater failures that would lead to an increase in emissions beyond the thresholds stated in the appropriate regulations.

The diagnosis shall be carried out by determining whether the measured oxygen sensor ceramic temperature falls below set limits over a number of measurement cycles. The evaluations of the diagnosis cycle are determined after the completion of a limited number of monitoring cycles.

Deviations in the oxygen sensor ceramic temperature or the oxygen sensor not being operatively ready in a timely manner (because of a too low temperature) can lead to an increase in emissions above the applicable standards or prevent the sensor signal from being used as a diagnostic system monitoring device. Deviations may occur due to, for example, ageing of the heater element, defective wiring, increased heater circuit connector contact resistance, defective heater driver etc.

1.9.1 General description of the PCV-System

There are 3 tubes connected to the engine: The first of them conducts the blow by gases from the cylinder head cover to the separator, where the oil is separated from the air and lead back by a second tube to the crankcase sump. A third tube directs the cleaned blow by gases via the intake system to the combustion. The pressure regulator makes sure that the high vacuum level between crankcase and ambient air will be reduced if needed.

1.10.1.1.1 Monitoring description

The coolant thermostat monitoring is done to detect a slow warm-up due to heat losses through thermostat and radiator. It is based on the comparison of the measured ECT sensor signal and the calculated ECT model (TCO_SUB).

The ECT model calculation is depending on the speed of the water pump, engine load and ambient temperature.

A malfunctioning coolant thermostat is detected, if the calculated ECT model (TCO_SUB) has exceeded the threshold 1 (thermostat regulation temperature) and the measured ECT sensor signal remains below threshold 2 (fault detection criteria).

Before a malfunctioning coolant thermostat is entered into failure memory, the conditions concerning low load, coasting duration and IAT during the monitoring are checked. If the monitoring conditions are met, the coolant thermostat is entered into failure memory. Otherwise the coolant thermostat monitoring is inhibited for this driving cycle.

Example of Monitoring Method

Scheme 1

A comparison between the measured engine coolant temperature (ECT) and the fault detection criteria temperature is done after a specific time interval. The interval itself is based on the engine coolant temperature model.

If the measured engine coolant temperature (ECT) is higher than fault detection criteria (thermostat regulation temperature -11°K); the thermostat is concluded as normal thermostat.

If the measured coolant temperature (ECT) is lower than fault detection criteria (thermostat regulation temperature -11°K), the thermostat is concluded as opened stuck thermostat.

TEMPERATURE RESISTANCE CHART

1.10.2.1.1 General Description

The purpose of this diagnosis is to detect electrical faults of the sensor signal. The input signal is analog from a NTC and has to be in a calibratable range. Short circuit to ground can be detected immediately. Short circuit to voltage battery or open load is detected, if conditions of Intake Air Temperature and Time After Start are fulfilled. If an error symptom is detected, the error counter is de-bounced.

1.10.2.2.1 General Description

The purpose of this diagnosis is to detect an implausible gradient on the coolant temperature signal. The diagnostic function checks whether the difference between one measured coolant temperature value and the succeeding value is too big.

1.10.2.3.1 General Description

The purpose of this diagnosis is to detect a stuck coolant temperature signal. The diagnostic function checks if after a variation of the calculated coolant temperature also a variation of the measured coolant temperature is detected. The range of required variation depends on ECT at engine start.

For RBM handling the Cold Start Denominator will be considered.

1.10.2.4.1 General Description

The purpose of this diagnosis is to detect a coolant temperature signal that is stuck in high range. The diagnostic function checks if after a certain time engine stopped, the engine temperature has reached a plausible (low) value, i.e. the engine has cooled down.

If the measured engine temperature at engine start is above a calibratable threshold and the diagnosis conditions are fulfilled, the error is set. The threshold depends on Intake Air Temperature at Start and the Time Engine was stopped.

For RBM handling the Cold Start Denominator will be considered.

1.10.3.1 General description

The engine off time is calculated using a relative time counter obtained from the instrumentation via CAN message. The difference in value of the relative time counter at last engine stop and at current engine start is compared to the corresponding values of ECT. An error is detected when engine off time is adjudged too small after a relatively large drop in ECT, or, conversely, when engine off time is too large after a small drop in ECT.

1.11.1.1.1 Idle Speed Control - General Description

This diagnosis monitors the stability of the idle speed. If the actual idle speed is not within a calibratible range, above or below the idle speed set-point then the failure criteria is fulfilled. The appropriate DTC will be stored.

Scheme 2

EMS PARAMETER DESCRIPTION CHART

1.13.1.1.1 Description of Control deviation of the camshaft position controller: ("target + slow response")

In this diagnosis module 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 the established threshold, a counter is started. The counter is incremented twice per crank revolution (but not exceeding 10 msec-rates).

If the counter exceeds a limit (also adjustable), a Rationality Fault (DTC) is stored.

The control deviation diagnosis has got an interface to the Rate-Based Monitoring module.

1. In-use monitor performance Ratio: The incrementing of the numerator, denominator, and the ratio calculation for the Variable Camshaft Timing monitor is executed by the Rate-Based Monitoring module. Like all monitors for which a standardized track and report in-use performance is required, the Variable Camshaft Timing monitor reports to the RBM-module via status flags.
2. Conditions for incrementing the Numerator: The numerator is incremented if and only if the monitor is not inhibited due to stored faults and the diagnostic has been performed and a fault would have been detected.
3. Conditions for incrementing the Denominator: The denominator is incremented if the monitor is not inhibited due to stored faults, the general driving conditions have been fulfilled and all additional physical conditions for incrementing have been fulfilled.

1.13.1.2.1 Description

The purpose of the diagnosis is to detect when the camshaft reference position is outside the designed range relative to the engine position from crankshaft and to detect a signal which is not valid.

The diagnostic strategy for inlet and exhaust camshaft is identical.

1.13.1.3.1 Description

The purpose of the diagnosis is to validate the camshaft signal used for synchronization. First the intake camshaft is selected for synchronization. If validation fails, the exhaust camshaft signal will be selected for synchronization. If validation also fails, no synchronization will be established.

1.13.2.1 Description

The purpose of this diagnostic is to check the integrity of the crankshaft sensor signal and/or electrical malfunctions. (Open line, SCG, SCVB)

1.15.2.1.1 General Description

The purpose of this diagnosis is to detect electrical faults as defined in OBDI requirements. The input signal is a CAN message of instrument cluster. If an error is detected by the instrument cluster, the error symptom is sent via CAN to the ECU. The ECU then debounces the error and stores it in the error management.

1.15.2.2.1 General Description

This diagnosis is performed in order to detect a stuck or not plausible AAT signal which cannot be detected by electrical range diagnosis.

The first part, just after start looks on the change of ambient temperature and compares the start and stop temperature. If the check is positive the diagnosis is finished. In negative case diagnosis runs to next step during warm up phase.

The error detection is only performed if the monitoring conditions for time after start, engine state idle speed, time of engine stop, ECT and ambient temperature are fulfilled. The plausibility error is detected if the absolute value of the temperature-difference between the arithmetic mean of engine coolant temperature ECT and temperature intake air IAT and the ambient temperature AAT (in formula: ABS (absolute value) of [(ECT+IAT) x 0,5 - AAT)]) exceeds the threshold for an anti-bounce time.

The error validation is only performed if ECT signal is valid and the vehicle was driven with a certain vehicle speed. If both conditions are true and an error was detected, then the error is set for this driving cycle and the diagnosis is switched off.

For RBM handling the Cold Start Denominator will be considered.

1.15.3.1.1 General Description

The purpose of this diagnosis is to detect electrical faults as defined in OBDI requirements. The input signal is analog from a NTC and has to be in a calibratable range. Short circuit to ground can be detected immediately, short circuit to voltage battery or open load after a delay time. If an error symptom is detected, the error counter is de-bounced.

1.15.3.2.1 General Description

This diagnosis checks IAT integrity for a plausible range and signal stuck.

For the range detection, IAT has to be within coolant temperature and ambient temperature window. If IAT is outside of the range plus an offset, the error symptom is set and the error counter is de-bounced.

If the vehicle was driven with a certain vehicle speed for a calibratable time (IAT sensor cool down) and afterwards the vehicle was in idle for a calibratable time (IAT sensor hot up), the IAT signal must have moved. If the signal has not moved after a calibratable number of cool down/hot up phases, a stuck IAT signal is detected and the error is de-bounced.

For RBM handling the Cold Start Denominator will be considered.

1.15.4.1.1 Monitoring Descriptions

P2100

ETC Driver diagnosis (H-bridge): The ETC - H-Bridge IC continually checks the MTC if there is a short circuit to battery voltage or ground. In addition the IC is able to detect over temperature. This is performed internally to the ECU.

1.15.5.1.1 Monitoring description

For a variable valve lift engine, the main function of the throttle body is to control the pressure in the intake manifold. Therefore the manifold differential pressure plausibility check is testing the plausibility of measured intake manifold pressure in comparison to the measured throttle position. So no throttle position acquisition error must be present.

The set-point of the differential intake manifold pressure is up to 60-70% of maximum torque request constant 5 kPa beneath ambient pressure. At higher load the differential pressure set-point becomes Zero.

In case the set-point of the differential pressure in the intake manifold is > 3 kPa beneath the ambient pressure, a differential pressure controller is active. The output of the controller is monitored. The output of the manifold pressure controller has to be between adjustable MIN/MAX-thresholds. If the MIN/MAX thresholds are exceeded a time counter is incremented. After this counter reaches the threshold within one diagnosis cycle, a manifold differential pressure sensor malfunction is detected.

1.15.5.2.1 General Description

The purpose of the diagnosis is to detect electrical faults as defined in OBDI requirements. The input signal has to be in a calibratable voltage range. Short circuit to battery or open load and short circuit to ground can be detected. If an error symptom is detected, the error is de-bounced.

1.15.5.3.1 General Description

The purpose of the diagnosis is to detect an improper offset on the signal of differential manifold pressure sensor (e.g. because of ageing). The absolute signal deviation from a setpoint is estimated. The threshold for detecting a failure depends on modelled temperature of the differential manifold sensor. The diagnosis is active during powerlatch phase. The error symptom is de-bounced.

1.15.6.1.1 Monitoring description

Depending on engine speed, valve-lift, inlet camshaft position, outlet camshaft position and manifold pressure an air mass flow into the cylinder is calculated. There is also a correction of the calculated air mass flow depending on intake air temperature, coolant temperature and ambient pressure. The ratio between the measured air mass flow and the calculated air mass flow must be between adjustable MIN/MAX-values. If the MIN/MAX thresholds are exceeded, a time counter is incremented. After this counter reaches the threshold within one diagnosis cycle, an air mass flow meter malfunction is detected.

1.15.6.2.1 General Description

The purpose of the diagnosis is to detect electrical faults and range violations of the mass air flow sensor.

If the period time is over a threshold or no edges are measured, a electrical or upper range failure is indicated. A lower range failure is also checked with a threshold.

After setting the error symptoms, the failure is de-bounced.

1.15.7.1.1 General Description

The purpose of the diagnosis is to detect faults of the knock sensor. Therefore the signal range and dynamics of a low pass filtered knock signal is checked.

If the signal range exceeds a upper or lower threshold a failure is detected.

An implausible knock signal is detected by using a statistical analysis. The difference between filtered knock signal and raw knock signal is estimated for a certain number of combustion cycles.

All error symptoms are de-bounced.

1.15.8.1 Monitoring overview

The electronic control of the Variable Valve Lift (VVL) is dependant on, Voltage Limits, Adaptations, current and power stage temperature. The following errors will be detected in this system.

Variable Valve Lift Electrical Diagram

Scheme 3

1.15.8.3 Monitoring overview - DC Motor current, power stage temperature and DC Motor overload

DC Motor current, power stage temperature and DC Motor overload is monitored through the ECU. This diagnosis checks for over-temperature and short term/long term current overload conditions (looks for current spikes over a threshold, and time vs. current table based)

1.15.8.11 Monitoring overview - sensor diagnosis

Sensor diagnosis is performed internally to the ECU and checks the sensor supply voltage to tunable boundaries. A sensor signal versus an internal sensor self check will determine the integrity of the sensor.