Self Diagnosis - Theory & Operation (N63): Overview BMW X6 E71

1.1.1 Diagnostic overview

Catalyst monitoring is based on the monitoring of the oxygen storage capability (OSC) by comparing the signals of the O2 sensor upstream and downstream of 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.

1.6.7.1 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 above diagnosis detected a fault.

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-361401-S30435016282010051400000) 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-361401-S30435016282010051400000) 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.

1.13.2.1 Diagnostic overview

The detection of each camshaft position is done by an active hall sensor and a cam wheel, "3 asymmetric teeth". The camshaft sensor delivers 3 high and 3 low phases of different length per 720°CRK. The high or low level of the signal at the reference gap of the crankshaft signal determines the position of the engine within the combustion cycle. With that information, a engine position is calculated from the crankshaft position sensor within a range from 0 to 720 °CRK.

The following malfunctions are detected

INTAKE AND EXHAUST REFERENCE

1.13.4.1 Diagnostic overview

The detection of crankshaft position is done by an active hall sensor and a crank wheel, "e.g. 60 minus 2 teeth". A reference gap, "e.g. of two teeth" allows the detection of the top dead center of cylinder 0. The crankshaft sensor delivers a certain number of high and low phases per 360°CRK. The transition from high to low is a falling edge; from low to high is a rising edge. Only the falling edges are counted. The difference between two falling edges is 6° CRK.

The following malfunctions are detected

CRK SENSOR SIGNAL REFERENCE

A teeth counter is incremented at every falling edge of the CRK sensor signal. If plus or minus two teeth are detected during the last 360° CRK at the reference gap, the tooth number de-bounce counter will be incremented. If the counter exceeds a limit, a CRK tooth error is delivered to the error management.

If more then two teeth plus or minus are detected the CRK looses synchronization and a CRK sync de-bounce counter will be incremented. If the counter exceeds a limit, a CRK sync error is delivered to the error management.

The detection of a tooth period error is done by an acceptance window. The expected tooth period is multiplied and divided with an engine speed dependency factor. The result is a bottom and a top limit of tooth period, in which the transition from high to low of the electrical signal has to occur. If a tooth period is not valid, the tooth period error de-bounce counter will be incremented. If the counter exceeds a limit, a CRK tooth per error is delivered to the error management.

Detection of implausible crankshaft signal is based on the detection of CAM signals without receiving correct CRK signal. If 12 or more CAM edges are detected (eg. 2 working cycles), without valid synchronization of the crankshaft, then CRK plaus error is detected and delivered to the error management. If no CRK signal at all is received, the symptom is "missing signal", else the symptom is "implausible signal".

1.14.5.4.3 Description Adaption Function

The TPS adaptation includes the following functions

Scheme 20

1. Adaptation and check of the limp-home position
2. Adaptation and check of the lower mechanical stop
3. Lower return spring check
4. Adaptation of the amplifier amplification (TPS 1 channel)
5. Upper return spring check

The state variable TPS_AD_STEP indicates the following adaptation steps

TPS ADAPTATION FUNCTION CHART

1.14.5.4.4 Description Start Check Function

1. Limp-home position check
2. Adaptation of the limp-home position
3. Upper return spring check

The start check is only carried out when the adaptation conditions are maintained otherwise it will be ignored without error entry.

Scheme 21

The state variable TPS_AD_STEP indicates the following start check steps

TPS ADAPTATION FUNCTION CHART