2.2 Generic OBD-II Drive Cycle
For each monitoring strategy, the OBD-II drive cycle to be used is stated. The purpose of the drive cycle is to run the onboard diagnostics monitoring strategy under consideration. The number of drive cycles that must be completed in order to illuminate the MIL is given in the Monitoring Operation table for each monitoring strategy. The drive cycle should be performed after any Diagnostic Trouble Codes (DTCs) have been erased from the ECM's memory, or after the battery has been disconnected.
3.1.5 Using Table 5
Table 5 contains specific Mode $06 related data. This table is to be used as a tool to cross reference any data received by a generic scan tool and identify any On-Board Diagnostic Monitor ID, PCODE, TID, Min, Max Values and scaling information.
Scheme 53
Scheme 54
Scheme 55
Recording segment time and position, and its manipulation
The monitor records crank angle time data every 30° of rotation with a 250 nanosecond measurement accuracy. Each 30° period is known as a 'segment'. The starting point of the segments relative to Top Dead Centre (TDC) firing and the number of segments used can be defined for each application so as to give the best and most robust probability of misfire detection. To maintain good detection across the entire engine speed range the measurement period can be altered between low and high engine speeds. The engine speed at which the measurement period is altered, if any, is determined by experiment.
Additionally, a third measurement period is defined for detection during start-up and when catalyst warm up ignition retard is being used after engine start.
The angular speed of the crankshaft during the ignition stroke is calculated using the segment data, multiplied by a scaling factor for easier storage in the ECM's memory, manipulated further and stored for each cylinder firing
Misfire 'signal' calculation
Where calculated adaption values have been stored in memory the adaptive signal will be calculated. This signal generally has the best opportunity to detect. However, the signal requires data in each speed breakpoint to interpolate between. If there is a breakpoint where no adaptions have been stored then the adaptive signal will only be used for misfire judgements up to the breakpoint immediately below it. For example if there is adaption data stored in memory up to 2000 RPM but none at 2500 RPM the adaptive signal will only be used up to 2000 RPM.
To support detection across the entire engine speed range further misfire 'signals' are calculated. These signals are not adjusted for errors in crank angle tolerance. These signals typically give good probability of detection at low engine speeds but become less effective at higher engine speeds.
Misfire judgement
Misfire judgements are delayed by one firing cycle. This is to allow comparison of the signal with the cylinders that fire before and after it, eliminating 'noisy' signals. Should the monitor repeatedly eliminate the signal over 5 consecutive firings on the same cylinder the monitor will assume that two adjacent cylinders are misfiring, ignore the signal check and allocate the 5 eliminated misfire judgements to the appropriate cylinder.
Adapted and un-adapted signals are compared to their respective thresholds in series. The diagram below illustrates the behavior of the 'adaptive' misfire signal with 1.0% intermittent misfire applied (data taken from a typical 8 cylinder application) and its judgement threshold.
Should one signal cross the threshold, indicating a misfire, the other methods will be skipped in order to prevent multiple counting of the same misfire event.
Scheme 56
Catalyst damage judgement
If 200 revolutions of misfire judgements have been made the monitor will make an assessment as to whether 'catalyst damage' levels of misfire have been exceeded or not. The failure level is determined from a look up table. The sum of individual cylinder misfire counters is then compared against this threshold. If the failure threshold is exceeded then the MIL will illuminate and the appropriate DTCs will be stored.
Storing adaption values in back-up memory
If no misfires have been recorded for the last 'catalyst damage' judgement, and sufficient temporary adaption calculations have been made, the temporary adaption data calculated for each cylinder will be stored in 'back-up' memory for the appropriate engine speed breakpoint.
If a single misfire is counted for the last 'catalyst damage' judgement, all temporary adaption data will be reset, along with the temporary calculation.
Once data has been stored in memory it can be updated but will not be erased, even after a battery reset.
Excess emissions judgement
If 1000 revolutions of misfire judgements have been made the monitor will make an assessment as to whether 'emissions failure' levels of misfire have been exceeded or not. The failure level is a single threshold value. The sum of individual cylinder misfire counters is compared against this threshold. If the failure threshold is exceeded then the MIL will illuminate and the appropriate DTCs will be stored.
Monitor execution check
Different monitor enable conditions are checked depending upon the operating condition of the engine (for example, fewer conditions apply during engine start). If all the appropriate enable conditions are met the monitor execution flag is set.
Adaptive learning execution check
Specific operating conditions necessary for learning misfire 'adaption' values are checked and the adaption execution flag set as appropriate.
Rough road and low fuel level judgement
A rolling average of 'delta' wheel speed data is calculated from ABS vehicle speed data transmitted over the CAN. This data is compared to calibrated thresholds to determine if the vehicle is being driven over a rough surface that might cause misdiagnosis of a misfire. If a rough road judgement is made the appropriate flag is set and taken into account the next time monitor execution conditions are checked.
An additional DTC is stored alongside the misfire DTCs if the fuel level is below a calibrateable level. This is to indicate that a possible cause of the misfire DTCs was low fuel level.
Scheme 57
Scheme 58
Scheme 59
Scheme 60
Scheme 61
Scheme 62
Circuit Continuity
Circuit continuity is checked by monitoring the commanded and the actual state of the EVAP canister purge valve. If the commanded and actual states do not match, a timer is started. If the states do not match within the timed period then a failure is registered. If the failure occurs on two drive cycles then the appropriate DTC is logged.
Flow Check
The purge flow monitor works continuously and is designed to detect low purge flow caused by a blockage in the purge system or a malfunctioning EVAP canister purge valve.
The basis of the diagnostic is to detect the presence of intake pressure pulses caused by the 10 Hz pulse width modulated control of the EVAP canister purge valve duty (as shown in the purge operation diagram below).
A discrete Fourier transform (DFT) calculation is used to help distinguish these pulses from other noises present in the intake pressure signal.
Scheme 63
Purge operation
Scheme 64
Scheme 65
Scheme 66
EGR Valve Range or Performance Failure
The EGR valve is checked by forcing it open and closed during a fuel cut. A reading from the MAP sensor is checked before, during and after the valve operation. The difference in the values between the open and closed state of the valve is compared with a map of engine speed and altitude versus the difference value. If this calculated value is below the threshold, then a fault is present.
Scheme 67
Scheme 68
Scheme 69
4.5.3 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.6.1 Upstream Oxygen Sensor High Low Monitor
This monitor is designed to detect continuous and intermittent faults with the upstream oxygen sensor signals. The monitor will operate continuously provided the entry conditions are met and the monitor is not inhibited for any of the reasons listed in the following table.
The upstream oxygen sensors current/voltage and impedance are compared to failure thresholds. If the signals are higher or lower than a predefined amount, a timer is started. A fault flag is set if the timer exceeds a threshold, otherwise a normal flag is set.
A general flowchart of the operation of the monitor is shown below.
Scheme 70
4.6.2 Upstream Oxygen Sensor Slow Response
The upstream oxygen sensor slow response monitor operates once per drive cycle.
The monitor will be started once all the entry conditions are met. The fuelling is then cycled rich and lean by a set value. The time taken for the upstream oxygen sensors to register this fuelling shift is known and after this has time has elapsed a calculation of the air fuel ratio read by the sensor is made and divided by the expected increase or decrease.
This ratio is accumulated over a set number of fuelling shifts from rich to lean and lean to rich before a result is obtained. This ratio is lower for a faulty sensor than it is for a correctly functioning part. If the diagnostic produces a ratio that is over a calibrated threshold a "normal" judgement is made, if the ratio is below the calibrated threshold then the diagnostic will be repeated. If the next measured ratio from the sensor is again below the calibrated threshold then that sensor is faulty and the relevant DTC will be stored and the MIL illuminated. Otherwise, the sensor is judged to be fault free.
The following flow chart shows the operation of this monitor.
Scheme 71
4.6.3 Upstream Oxygen Sensor Slow Activation
This monitor is used to check that the upstream oxygen sensors are operating correctly after their heaters have been turned on.
After the engine has started, the upstream oxygen sensor heaters are activated after a delay time. The monitor checks the change in impedance of the upstream oxygen sensors due to the heating. If the impedance level has not dropped by a defined level in a defined amount of time, then a failure will be detected.
The general flowchart of the monitor is shown below.
Scheme 72
4.6.4 Downstream Oxygen Sensor High or Low Monitor
This monitor checks the downstream oxygen sensor for an electrical circuit fault. There are three parts to this monitor.
- High
- Low or Open circuit
- Short to battery
The short to battery diagnostic detects a fault that results in a downstream oxygen sensor voltage that is too high (e.g. a short circuit to the battery). If the voltage exceeds the short to battery threshold then a fault counter will be incremented. When the fault counter exceeds a pre-determined value a DTC will be stored.
The high diagnostic is designed to detect a fault that results in a downstream oxygen sensor voltage that is permanently too high, but not high enough to detect a short to battery situation. It monitors the voltage achieved by the downstream oxygen sensor after an over run fuel cut off. The maximum and minimum voltages are compared and if the difference between the two is below a threshold, a DTC will be stored.
The low diagnostic detects a fault that results in a downstream oxygen sensor voltage that is permanently too low. It monitors the minimum voltage achieved by the downstream oxygen sensor after engine start. If, after the entry conditions are met, the voltage is still too low then a fault counter is incremented. If the fault counter exceeds a pre-determined value then a DTC will be stored.
The following flowchart shows the operation of this monitor.
Scheme 73
4.6.5 Downstream Oxygen Sensor Stuck Monitor
This monitor checks if the downstream oxygen sensor voltage has been at a constant voltage during an overrun fuel cut off.
The stuck diagnostic is designed to detect if the downstream oxygen sensor voltage is permanently stuck at a voltage, but which is still within its normal operating range. If the entry conditions are met and the fuel system and oxygen sensors are in working order, the downstream oxygen sensor maximum and minimum voltages are continuously updated. After an over run fuel-cut has been performed, the difference in voltages before and after the fuel cut is compared. If the difference has not exceeded a threshold a DTC will be stored.
A general flow chart of the diagnostic is shown below.
Scheme 74
4.6.6 Downstream Oxygen Sensor Rationality Check
This monitor checks that the sub-feedback adaption values are within a specified range.
The diagnostic runs if the entry conditions have been met, all the oxygen sensors are working, the fuel system adaptions are within their limits and sub-feedback is operating. The monitor looks at the different sites of the sub-feedback system and checks how many sites are over the fault threshold. If a pre-determined number of sites have exceeded this threshold, then a fault will be detected.
A general flowchart of the operation of this monitor is shown below.
Scheme 75
Scheme 76
Scheme 77
Scheme 78
Scheme 79
Scheme 80
Scheme 81
Scheme 82
4.7.3 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.9.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.10.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.11.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
Sensor Stuck
This monitor checks that the engine coolant temperature sensor is not stuck at a particular value. If the engine has been off for longer than a calibrated time and the engine speed is over a calibrated limit, the engine coolant temperature must change by a calibrated amount before the engine oil temperature (EOT) has changed by a calibrated value or a failure will be detected. If the engine coolant temperature changes by an amount equal to or greater than this threshold then a normal judgement is made.
Range or Performance Failure
This monitor checks that the engine coolant temperature sensor is reading the correct value when compared to other temperature sensors on the vehicle at ignition on.
If the engine has been off for longer than a calibrated time, the engine coolant temperature sensor reading is compared to the average reading of the sum of the intake air temperature (IAT) and ambient air temperature (AAT) sensors. The engine coolant temperature sensor must be within a calibrated threshold of this value for a normal judgement to be made, otherwise a fault will be detected.
Time to Closed Loop Fuelling
The engine coolant temperature is monitored to ensure it reaches the closed loop fuelling enable temperature. If the Intake Air Temperature is above the required level, the following strategy will be enabled.
A timer is incremented when the engine speed and mass airflow are above pre-determined thresholds. A normal judgement is made if the engine coolant temperature reaches the value for closed loop fuelling before the timer reaches the fault threshold.
A failure judgement is made if the 'load conditions met' timer reaches the fault threshold before the engine coolant temperature reaches the value required for closed loop fuelling.
The fault threshold is obtained from a look up table that is mapped against the engine coolant temperature at engine start.
Scheme 83
Scheme 84
Scheme 85
4.12.3 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.13.1 High or Low Input Failure and Ground Monitor
This monitor runs continuously. The voltage from the sensor is compared with failure thresholds defined in the software. If the sensor voltage is less than the minimum threshold, a timer will be started. If this timer exceeds a threshold, a failure flag is set and a DTC is stored. If the sensor voltage is greater than the maximum threshold, a timer will be started. If this timer exceeds a threshold, a failure flag is set and a DTC is stored.
4.13.2 Range/Performance Failure
This monitor runs continuously so long as the entry conditions are met. The Manifold Absolute Pressure (MAP) Sensor monitor compares the measured manifold absolute pressure with an estimated pressure, which is calculated by a model. The model that calculates the estimated pressure uses a look-up table using engine speed and throttle angle as inputs. These are used to derive base and compensation values for intake air temperature, atmospheric pressure, EGR rate and variable valve timing (VVT), from which the estimated pressure is calculated.
Judgement as to whether the MAP sensor is behaving correctly is made after the entry conditions have been fulfilled and the differences between the measured and estimated values are below calibrated thresholds. The MAP sensor is faulty if, when the entry conditions are met, the difference between the actual and estimated values is greater than a calibrated threshold. The monitor has the ability to make a normal judgement followed by a failed judgement or vice versa as the monitor runs continuously whilst the entry conditions are met.
Scheme 86
Scheme 87
4.13.4 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.14.1 High or Low Input Failure and Ground Monitor
This monitor runs continuously. The voltage from the sensor is compared with failure thresholds defined in the software. If the sensor voltage is less than the minimum threshold, a timer will be started. If this timer exceeds a threshold, a failure flag is set and a DTC is stored. If the sensor voltage is greater than the maximum threshold, a timer will be started. If this timer exceeds a threshold, a failure flag is set and a DTC is stored.
For Mass Airflow (MAF) sensor short to ground or open circuit monitoring, the voltage on the ground pin of the Mass Airflow sensor is monitored in the same way as described above.
4.14.2 Range/Performance Failure
This monitor runs continuously so long as the entry conditions are met. The Mass Airflow Sensor monitor compares the measured airflow with an estimated airflow, which is calculated by a model. The model that calculates the estimated airflow uses a look-up table using engine speed and throttle angle as inputs. These are used to derive base and compensation values for intake air temperature, atmospheric pressure, EGR rate and VVT, from which the estimated airflow is calculated.
Judgement as to whether the Mass Airflow sensor is behaving correctly is made after the entry conditions have been fulfilled and the differences between the measured and estimated values are below calibrated thresholds. The Mass Airflow sensor is faulty if when the entry conditions are met, the difference between the actual and estimated values is greater than a calibrated threshold. The monitor has the ability to make a normal judgement followed by a failed judgement or vice versa as the monitor runs continuously whilst the entry conditions are met.
Scheme 88
Scheme 89
4.14.4 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.15 Barometric Pressure Sensor
The Barometric Pressure (BARO) sensor (also referred to as the High Altitude Compensation sensor) is located within the ECM.
4.15.1 High/Low Input Failure
These are continuous monitors. The voltage from the sensor is compared to failure thresholds defined in the software. If the voltage is less than the minimum threshold, then a timer starts to increment. Once this timer exceeds another threshold a failure flag is set and a DTC is stored. If the voltage exceeds the maximum threshold defined in the software, then a timer starts to increment. Once this timer exceeds another threshold a failure flag is set and a DTC is stored.
4.15.2 Range/Performance Failure
The signal from the sensor is compared to the signal from the MAP sensor at ignition on. During this time the pressure within the inlet manifold should be at atmospheric, and therefore should match the value from the barometric pressure sensor.
The following conditions must be met first before the monitor can execute
Engine speed = 0 RPM
Vehicle speed = 0 MPH
Monitor is not inhibited
Ignition on
Engine not cranking
Battery voltage exceeds minimum threshold
Engine coolant temperature is above minimum threshold
Atmospheric pressure within limits
Inlet manifold pressure value has stabilized
If the absolute value of the difference between the signal from the barometric pressure sensor and the MAP sensor is greater than a defined amount, a timer is executed. If the timer exceeds a calibrated threshold, a temperature failure is judged. Providing there is no failure of the MAP sensor, a DTC is then stored.
Scheme 90
4.15.3 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.16.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.17.1 Sensor Stuck
This monitor checks that the intake air temperature (IAT) sensor is not stuck at a particular value. If the airflow into the engine exceeds a threshold for longer than a calibratable time, the Intake Air Temperature sensor reading is stored. The next time the airflow into the engine drops below a second threshold and the engine is at idle, a second timer is incremented. Once this timer reaches a pre-determined value, the Intake Air Temperature sensor reading is again stored. The high flow temperature is then subtracted from the low flow temperature and if the difference is greater than a threshold a normal judgement is made. If the difference is less than the threshold a failure will be detected.
4.17.2 Range or Performance Failure
This monitor checks that the Intake Air Temperature sensor is reading a correct value when compared to other sensors on the vehicle.
If the engine has been off for longer than a calibrated time period, when the ignition is turned back on the Intake Air Temperature sensor reading is compared to the average of the sum of the Engine Coolant Temperature sensor and Engine Oil Temperature sensor. The Intake Air Temperature sensor must be within a calibrated threshold of this reading for a normal judgement to be made. If it is outside this threshold then a failure is flagged.
Scheme 91
Scheme 92
Scheme 93
Scheme 94
Scheme 95
Scheme 96
4.17.4 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.18.1 Sensor Stuck
This monitor checks that the engine oil temperature (EOT) sensor is not stuck at a particular value. If the engine has been off for longer than a calibrated period of time and the engine speed has exceeded a calibrateable level, then the engine oil temperature must change by a calibrated amount within a set time period after engine start, or a failure will be detected. If the engine oil temperature changes by an amount equal to or greater than this threshold a normal judgement is made.
4.18.2 Range or Performance Failure
This monitor checks that the EOT sensor is reading a correct value when compared to other sensors on the vehicle at ignition on.
If the engine has been off for longer than a calibrated time, the EOT sensor reading is compared to the average of the sum of the ECT sensor and AAT sensor. The EOT sensor must be within a calibrated threshold of this reading for a normal judgement to be made. If it is outside this threshold then a fault will be detected.
Scheme 97
Scheme 98
4.18.4 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.19.1 Sensor Stuck
This monitor checks that the fuel rail temperature (FRT) sensor is not stuck at a particular value. If the engine has been off for longer than a calibrated time, the next time the engine is started the diagnostic will run.
If the engine speed exceeds a calibrated limit, the fuel rail temperature must change by a calibrated amount within a set period of time after engine start or a failure will be flagged. If the fuel rail temperature changes by an amount equal to or greater than this threshold a normal judgement is made.
4.19.2 Range or Performance Failure
This monitor checks that the fuel rail temperature sensor is reading a correct value when compared to other sensors on the vehicle.
If the engine has been off for longer than a calibrated time period, when the ignition is next switched on, the fuel rail temperature sensor reading is compared to the average of the sum of the ECT sensor and AAT sensor. The fuel rail temperature sensor must be within a calibrated threshold of this reading for a normal judgement to be made. If it exceeds this threshold, then a fault will be detected.
Scheme 99
Scheme 100
Scheme 101
4.19.5 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.20.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.21.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.22.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.23.1 Crank request Signal
The crank request signal is continually monitored for the presence of a signal whilst the vehicle is in motion. Vehicle motion is confirmed by checking vehicle speed, engine speed and engine load. If the crank request signal is detected for longer than the defined time a failure is registered. The crank request signal is also monitored to confirm the signal is available when a crank request is required.
4.23.2 Park/Neutral Switch
During the engine cranking operation, if the park/neutral input is low while the CAN signal from the transmission is indicating that park/neutral is selected; the low fault timer is enabled. When the low fault timer reaches the calibrated time, the low fault flag is set.
If the park/neutral input is high and the vehicle is detected as moving with an appropriate engine load, then the high fault timer will be enabled. When the high fault timer reaches the calibrated time, the high fault flag is set.
4.23.3 Starter relay
The starter relay is controlled by the ECM in response to a valid crank request signal when the vehicle is stationary and park or neutral are selected. A failure of the starter relay circuit will be registered if the starter relay drive signal from the ECM is on but the starter relay feedback indicates that the relay is off, or vice versa.
Scheme 102
4.23.4 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.24.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.25.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.26.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.27.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.28.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.29.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.30 Variable Valve Timing
The Variable Valve Timing (VVT) system consists of an actuator built into the camshaft chain sprocket and an Oil Control Valve (OCV) which controls the flow of oil to the camshaft actuator. The system is controlled via the oil control valve and camshaft position sensors. The oil control valve varies the oil flow into the camshaft actuator and creates a variable offset between the camshaft and the camshaft sprocket; feedback for this system is provided by the camshaft position sensors.
4.30.1 Hardware Check
This monitor checks the oil control valve on both Banks A and B. The commanded and the actual state of the valve are continually checked as long as the PWM drive signal remains within limits. If the commanded and the actual state differ for longer than a predefined time period then a failure is registered. The ECM determines the type of failure by examining which state the valve was unable to attain and the output signal to the valve. If a failure is registered on two drive cycles, the MIL will illuminate.
4.30.2 Camshaft Position
The camshaft position sensors are used to monitor the actual level of camshaft advance/retard against the target level. If the target and actual values do not match for a calibratable period of time a failure is registered. If a failure is registered on two drive cycles, the MIL will illuminate.
Scheme 103
4.30.3 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.31 Controller Area Network System
The Controller Area Network (CAN) system is monitored by the ECM for the following conditions.
4.31.1 Invalid signal Error
The ECM is continually receiving data from a number of other control modules via the CAN system. If one of these control module identifies a problem within its own system that causes it to be unable to transmit valid data, it will a store DTC locally and transmit an error marker (a specific default value of the data that indicates an error) on the CAN system. When the ECM identifies an error marker from another control module, it also logs a failure.
4.31.2 Loss of Communications
All the control modules on the CAN system transmit data continually. If messages from one or more of the control modules are not seen by the ECM within a predefined time, it will register a loss of communications fault.
Scheme 104
4.31.3 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.32 Fuel Level Sensor
There are two parts to the Fuel Level Sensor monitor. The output of the Fuel Level Sensor is monitored to ensure it changes as fuel is used. It is also monitored for a noisy signal, when the vehicle is stationary and fuel movement is expected to be at a minimum.
4.32.1 Fuel level stuck monitor
The fuel level is continuously monitored. The fuel level should change by more than a set percentage before a calculated amount of fuel is used. This process will operate through cumulative trips if necessary. Once the fuel level changes by the amount required the process is reset and starts again. If the fuel used threshold is reached before the fuel level changes by the required percentage, a temporary fault will be stored. A second occurrence will cause a permanent fault to be stored, however the MIL will not illuminate.
4.32.2 Fuel level noisy monitor
Once the fuel level percentage has changed to satisfy the stuck monitor described above and a number of other entry conditions have been satisfied, the system will complete a fuel level noisy test during the next available idle. When the vehicle comes to rest, fuel movement is allowed to subside and the output of the fuel level sensor is monitored for a short period of time. During this period the output of the fuel level sensor is integrated and compared to a failure threshold. This process is repeated as the fuel level falls. If the failure threshold is exceeded a temporary fault will be stored. A further failure in the next trip will cause a permanent fault to be stored, however the MIL will not illuminate.
Scheme 105
4.33.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
Rationality Check
The signal is checked for rationality against the Intake Air Temperature sensor. When the entry conditions have been met the difference between the two sensors is calculated. If the difference is greater than 30 °C for a predefined period of time then a failure is registered. If the problem occurs on two drive cycles then the MIL will illuminate. The DTC which is logged depends on whether the ambient air temperature sensor signal is lower or higher than the intake air temperature sensor.
Range/Performance
If the instrument pack detects a failure in the ambient air temperature sensor it will output a constant default value. The range/performance check monitors for a stuck signal at this default value for longer than a predefined period. When this occurs a failure is registered. If the problem occurs on two drive cycles then the MIL will illuminate.
Scheme 106
4.34.2 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.35.3 Drive Cycle Information
The generic drive cycle (see 2.2 GENERIC OBD-II DRIVE CYCLE ) applies.
4.36 Air Conditioning (A/C) System Component Monitoring
No engine control strategies are altered when the air conditioning system is on and no electronic air conditioning system components are used as part of the diagnostic strategy for any other monitored system or component. Therefore, the OBD II system does not monitor any of the air conditioning system components.