Description
In the air path, two mass airflows are computed (one at the throttle and one at the cylinder). In order to take into account engine -to -engine variations, an adaption is made which will ensure the convergence of the mass air flow at the throttle and the cylinder.
In the case of an air leak, the throttle will naturally close and thus the MAF at the throttle (which is computed from manifold pressure at the throttle and throttle opening) will decrease. The mass air flow at the cylinder (which is computed from manifold pressure) will increase because of the air leak. When the divergence of these two values reaches a threshold, an error flag is raised.
Scheme 216
When an air leak in the air intake system is detected the engine speed is limited to 2000 RPM.
The camshaft sensor signal presents one edge (rising or falling) per engine revolution. The position of these edges is known relative to crankshaft long tooth position.
A plausibility diagnosis is performed that compares camshaft (CAM) and crankshaft signals. The CAM edge must be in a defined window of crankshaft teeth in order to declare the CAM signal as valid.
If a CAM error is detected after the camshaft and crankshaft signals have synchronized the engine will remain in normal operation mode.
If insufficient time is available at engine crank (to determine the camshaft and crankshaft synchronization) for a Cam error to be detected then the correct firing cylinder cannot be determined. In this case
The sequential fuel injection will run with a constant injection phase of 180°CRK and the engine will run open loop (in this condition there is a 50% probability of the injection starting at the correct crankshaft position). This "Limp Home" condition minimizes the impact on engine responsiveness due to excessive time periods between fuel injection and inlet valve opening.
Each ignition coil is fired every TDC.
Knock correction will take a constant default value.
The diagnosis is different depending on whether it takes place before or after synchronization.
Before synchronization, a crankshaft error is detected if a number of plausible camshaft signal edges were detected and the system is still not synchronized with the crankshaft signal. After synchronization the number of teeth per revolution is monitored. Detection of more than two supplemental or missing teeth will reset the crankshaft signal acquisition.
Loss of the crankshaft signal after synchronization is detected as engine stop and the error will be detected as before synchronization.
For systems with a magnetic crankshaft sensor an electrical error can be detected by the extended MCPS diagnosis before or after synchronization. For systems with an active crankshaft sensor LV_CRK_OC_ERR is always 0.
After crankshaft error detection the system may operate in limp-home mode if applicable. If this is the case then the crankshaft signal will be simulated and no further functional diagnosis will be performed.
CAN bus error management will diagnose
- Missing frames coming from the CAN protocol
- Bus off mode on CAN protocol
- Lack of active nodes (any non-active nodes will be detected by monitoring one frame per ECU)
All checks are performed by the base software and will detect errors associated with the ASC frame, instrument pack, CVT1 frame, CAN protocol and any FTL value errors.
The purpose of this test is to check the status of the different ECU memory types and to give information regarding the ECU state. Most of the checks are performed during system start-up.
All failures are considered as permanent and no debounce management is allowed.
The self-test function carries out the following tests
- RAM areas test
- NVMY test
- Flash test
- Checksum test
General description
The solution chosen to fulfill this OBD requirement is based on Oxygen Storage Capacity (OSC)
During the diagnosis (special A/F pulses during engine steady state conditions), the downstream O2 sensor signal is analyzed to evaluate the OSC of the catalyst.
The OSC is correlated experimentally with the global hydrocarbon (HC) efficiency and HC emissions during the test cycle. It represents the quantity of oxygen that is really used for the oxidation-reduction reaction by the catalytic converter (stored during the lean excursion and consumed during the rich excursion).
Scheme 217
Description of the open loop diagnosis
Catalyst monitoring is a sequential diagnosis made during steady state conditions. This monitoring is intrusive (special A/F pulses during engine steady state conditions).
During the diagnosis phase the downstream sensor activity is measured and corresponds to the OSC of the catalyst. If this dynamic is high (low OSC) the diagnosis criteria is high (bad catalyst).
Scheme 218
If one of the monitoring conditions is not met or if the mass airflow deviates too much from the value stored at the start of this test phase, the test is interrupted. The test will then start again in steady state conditions.
If a problem has occurred with the downstream sensor during the catalyst diagnosis, a sensor diagnosis is done.
To check the plausibility of the coolant temperature sensor output (TCO) prior to closed loop fuelling, a modeled value of TCO (TCO_SUB) and an after start timer are used.
After starting the engine a timer is incremented (the timer is disabled by certain engine states such as fuel cut). Once both TCO_SUB and timer are above closed loop thresholds then, assuming all other conditions are met (idle speed, fuel cut, engine load and intake air temperature conditions), TCO failure detection is enabled.
If the coolant temperature sensor output is not above a threshold to enable close loop control, the error 'Insufficient Coolant Temperature for Closed-Loop Control' is flagged.
The purpose of the coolant thermostat is to effect a quick engine warm up after start. The thermostat is closed after engine start to limit the coolant circulation to the radiator until the thermostat regulating temperature is reached. If the thermostat is stuck open, the coolant circulation will not be limited after start and the engine warm up time will increase. This may cause an increase in emissions.
To monitor the thermostat function, a modeled value for coolant temperature is calculated.
This monitoring is used for diagnosing a leaking thermostat or a thermostat stuck in the open position. When the temperature model has reached normal operating temperature the actual coolant temperature is checked to confirm that it has been above the normal thermostat opening temperature for sufficient time. If this is not the case the thermostat is declared stuck open.
Graphs showing the diagnostic operation with typical calibration values are given below.
TCO: coolant temperature (sensor)
TCO_SUB: modeled temperature
Scheme 219
Normal thermostat operation
When TCO crosses 80.25°C, a timer is initialized and decremented (as long as TCO >80.25°C). When TCO_SUB crosses 90°C (C_TCO_TH_MIN) then a decision is made.
If the timer has elapsed then thermostat is declared OK.
Scheme 220
When TCO crosses 80.25°C, a timer is initialized and decremented (as long as TCO >80.25°C). When TCO_SUB crosses 90°C (C_TCO_TH_MIN) then a decision is made.
In this case timer has not elapsed and thus a failure is detected. The coolant temperature increase is too slow
Scheme 221
When TCO_SUB crosses 90°C then a decision is made.
In case that TCO has not reached 80.25°C, a failure "too low coolant temperature" is declared.
If the supply voltage is invalid then the sensors depending on it can deliver the wrong values and can be detected as faulty. Hence the reference voltages are obtained from the hardware input/output system and are monitored. The voltages must be within calibrated limits, both for absolute values and for voltage gradient.
The purpose of this monitor is to diagnose O2 sensor heater circuit electrical errors detected by the hardware and to detect a resistive problem with the O2 sensor heater element.
Note that the ECU supply to drive the oxygen sensor heater is pulse-width modulated (PWM)
The purpose of this monitor is to diagnose O2 sensor heater circuit electrical errors detected by the hardware and to detect a resistive problem with the O2 sensor heater element.
Note that the ECU supply to drive the oxygen sensor heater is pulse-width modulated (PWM)
The upstream sensor will cause an emission increase when its response time increases too much (A/F Loop period or frequency check).
The period of the A/F loop is measured and the number of lean/rich transitions are counted. The sum of valid periods is then calculated.
The corresponding limit period versus operating point is acquired.
A failure is detected when the sum of the measured periods exceeds the sum of the corresponding limit.
Description of the strategy
O2 sensor monitoring is a sequential diagnosis made during steady state conditions.
The diagnosis is composed of two main phases
- Measurement
- Diagnosis
The purpose of this monitor is to detect open circuit, short circuit and communication errors in the clutch solenoid. The diagnostic is performed by the gearbox interface box (GIB).
The purpose of this monitor is detect open circuit, short circuit, motor drive over temperature and motor drive defaulted errors in the CVT electrical motor. The diagnostic is performed by the gearbox interface box (GIB).
This functionality checks the integrity of the gearbox interface box and is performed by the hardware.
The purpose of this monitor is to detect open circuit, short circuit and communication errors in the secondary pressure solenoid. The diagnostic is performed by the gearbox interface box (GIB).
This function checks the integrity of the EM-CVT Ratio Control Motor by comparing the actual engine speed with the target engine speed over a period of time.
The procedure integrates a normalized version of the engine speed error for a set time period and then carries out a comparison when this time period expires. Many tests need to be performed in order for the motor to be diagnosed as faulty and, as such, a certain number of these have to fail. For this reason a safety de-bounce routine is also used by this diagnostic function.
The evaporative system monitoring uses a Tank Leak Detection Pump (TLDP). The TLDP is an electrically/vacuum-actuated device that pressurizes the evaporative emission system for the purpose of detecting leaks and verifying canister purge valve operation.
The misfire can be caused by many different conditions, including: injector failure, fuel pressure problems, combustion problems, ignition failure, etc and will increase the emissions and potentially damage the catalyst.
The fuel system diagnosis monitors the fuel delivery system for its ability to provide compliance with emission standards.
This diagnosis is continuously performed if enable conditions are fulfilled.
The fuel system diagnosis checks if the sum of short-term fuel trim (only based on upstream sensor voltage monitoring) and long term fuel trim (one additive & one multiplicative term) are within a band.
Out of this band a failure is detected (if cumulated time out of band is above a threshold).
Different fuel system problems may occur
- Fuel pressure problem: short term fuel trim deviation which induces emissions problem, but no effect on the catalyst window set point because of homogenous mixture, in steady engine conditions.
- Cylinder misdistribution problem due to injector failure: short-term fuel trim deviation with effect on the catalyst window set point because non-homogeneous mixture.
Engine speed deviation from the nominal engine speed set point is monitored when the vehicle is stopped.
If the engine is at idle for a given time and under normal conditions (engine load, coolant temperature, battery voltage and canister vent valve opening) then, if the difference between engine speed set point and actual value is too low or too high, an error is detected.
Each ignition coil is diagnosed separately. The hardware carries out the system checks and can diagnose 'short to ground', 'line break' or 'short to battery'.
Note that in the case of a confirmed short circuit to battery, the output driver is automatically deactivated for protection.
The purpose of this diagnosis is to detect electrical failures in the fuel injectors. These checks are carried out by the hardware.
The checks 'short circuit to ground', 'short circuit to battery' and 'line break' are made with the key on.
If a failure is detected ten times in one drive cycle then the relevant injector is shut down.
To check the plausibility of the knock sensor output it is compared to a modeled knock sensor signal.
If certain coolant temperature, engine speed and load conditions are met then, if the difference between knock sensor output signal and it's modeled value is above a threshold, a relative failure is detected.
An SPI Bus failure for knock can also be detected by the system hardware.
If one of these faults is detected, and certain engine conditions are met, then a limp home strategy can be implemented.
Under certain conditions the manifold pressure (MAP) sensor is checked for a coherent value against engine speed and throttle opening. These conditions are
- MAP too low when engine stopped (in these conditions, MAP cannot be lower than the minimum ambient pressure).
- MAP too low at idle speed engine running (in these conditions, the engine cannot run with too low manifold pressure)
- MAP too low at full load for low engine speed (in these conditions, MAP cannot be lower than the minimum ambient pressure)
- MAP too high in deceleration (the engine management system calibration is tuned so that the MAP target value is 200 hPa during deceleration).
In case of error on MAP acquisition, the MAP information will be built up by using engine speed and throttle position information.
This diagnosis is for Electronic Throttle Control driver failure and is performed by the component driver.
In normal conditions, throttle set point and actual value must correspond within a tolerance determined by controller performance under worst-case conditions (response time, overshoot, etc).
If an error is detected then MTC driver is switched off and engine speed is limited to a maximum of 2000 RPM.
The system has two sensors for throttle position. Signals from the two sensors are compared and must be within a given tolerance.
Two errors can be raised
- Small discrepancy: in this case it is difficult to identify which sensor is wrong. The system selects the highest one.
- Large discrepancy: a plausibility check is performed using engine speed and mass air flow in order to determine which sensor is providing incorrect information.
In case of discrepancy between the two pedal position sensors, the channel giving the smallest value is selected.
The SPI bus resides in the ECU and connects the knock detection chip with the main CPU. The diagnosis detects a connection failure and is performed by the system hardware.
The purpose of this monitor is to detect errors with the state of the PRNDM lever. Since the 'Plus', 'Minus' and 'Button' flags could be raised regardless of where the shift lever is, it is not possible to establish if a fault is present by considering the switches.
This routine considers the PRNDM flags and raises an error flag if a failure is recorded. It also writes a variable, to aid the diagnosis of the fault by counting up how many of the switches are closed.
The purpose of this diagnosis is to manage the diagnosis of the vehicle speed information through the CAN bus.
The output from both front wheel speed sensors is compared. If the outputs of both sensors are stuck 'high' then an error is declared.
This section describes a new monitor that checks the plausibility of the ambient temperature (TAM) sensor with the intake air temperature (TIA) sensor. The ambient temperature signal is an input to the engine control unit via CAN from the instrument pack ECU and is used as part of the OBDII rate based monitoring criteria. As such it needs to be monitored by the OBDII system. Electrical checks of the TAM sensor are made by the instrument pack ECU. The air intake temperature sensor is a direct input to the engine control unit and is used as input to several OBD strategies. The TIA sensor is already monitored for electrical continuity and intermittent failure.
The result of the plausibility diagnosis gives 1 fault code defined as 'TIA or TAM implausible' and it will be specified in the service manual to check both sensors if this failure occurs.
The first part of the diagnosis is the 'engine cold check' however if the cold check criteria exceed a range then second 'engine hot check' is performed. This is shown schematically below.
The PCV diagnostic functions in the EMS detect a disconnection of the PCV hose between the PCV valve and the intake manifold (Mini Cooper) or compressor inlet (Mini Cooper S).
The PCV valve mechanically screws into the Cam Cover. (Scheme 222) Also, it is not required that the PCV valve be removed during normal service procedures.
