On Board Diagnostics: Overview Jaguar S-type I рестайлинг

Scheme 1

Scheme 2

3.1 Functional Description

The purpose of mode $06 is to allow access to the results for on-board diagnostic monitoring tests of specific components/systems that are continuously monitored (e.g. misfire monitoring) and non-continuously monitored (e.g. catalyst system).

The request message for test values, consists of two bytes, byte #1 specifies what service is to respond e.g. $06 for Mode $06 request. Byte #2 specifies which On-Board Diagnostic Monitor ID (OBDMID) information is being requested i.e. any supported On-Board Diagnostic Monitor ID from $00 to $FF.

Scheme 3

4.1.1 Description

The Catalyst monitor operates once per trip. It waits until all entry conditions are met.

Once all the entry conditions are met, the monitor will start to run. The fuelling is cycled rich and lean by approximately 3% to achieve a reaction at the downstream exhaust gas oxygen sensor, this process is called dither. At the start of any monitoring period, a short delay (steady state condition check) will occur before the monitor is enabled to ensure that the fuelling is stable when the diagnosis takes place. If for any reason, the entry conditions are no longer valid, but the monitor has not yet completed then the result and execution time data are retained. If the entry conditions are again fulfilled, the monitor will resume with the stored data, unless there have been more than four attempts to run the check, in which case the monitor will clear the accumulated data and restart the diagnosis.

After the monitor has run for a calibrated period of time, the results are calculated. These are determined by accumulating the locus of the downstream exhaust gas oxygen sensor signal against the accumulation of the upstream exhaust gas oxygen sensor. The more active the downstream sensor, the less oxygen storage capacity the catalyst has, resulting in a correspondingly higher locus value. With a correctly operating catalyst, the downstream sensor is not so active, so lower locus values are obtained than would be recorded with a faulty system.

If the accumulated count is lower than a calibrates threshold then the catalyst diagnostic test has been passed. If the accumulated count equals or exceeds the calibrates threshold then the catalyst system has a problem and the appropriate DTC will be stored.

Scheme 4

Scheme 5

4.2.1 Description

The misfire detection monitor runs continuously and is designed to detect levels of misfire that can cause thermal damage to the catalyst or result in excessive tailpipe emissions. Determination of a misfire is made by analysis of changes in crankshaft speed, since a misfire will cause a fall in speed after a faulty firing event. This data is analyzed in four ways to ensure the detection of all possible combinations of misfire.

The results of the misfire judgement process for each firing event are used to determine whether two failure levels have been met, 'catalyst damage' misfire and 'excess emissions' misfire. Each fault judgement process has its own failure threshold and calculation period.

The following fault conditions can be identified by the monitor

1. Cylinder 1 (1A) misfire
2. Cylinder 3 (2A) misfire
3. Cylinder 5 (3A) misfire
4. Catalyst damage misfire
5. Low fuel level misfire
6. Cylinder 2 (1B) misfire
7. Cylinder 4 (2B) misfire
8. Cylinder 6 (3B) misfire
9. Excess emissions misfire
10. Multiple cylinder misfire

The misfire monitor operates continuously within the boundaries of the regulated monitor operation window, as shown below.

Scheme 6

After engine start, the monitor will be enabled as soon as the engine speed rises above the minimum operation speed (150 RPM below fully warm stabilized idle speed). Two revolutions of crank angle data, i.e. One sample of data from each cylinder firing, must then be 'buffered' before any decisions can be made by the monitor. Before engine speed has reached the top of the start flare the monitor will be ready to make misfire judgments, which are then made on every cylinder firing, irrespective of whether the monitor is enabled or not.

Scheme 7

4.3.2 Description

The evaporative monitoring system being used permits the detection of leaks with a diameter of 0.5 mm (0.020") or greater.

This is achieved by means of a pressure test of the system. This is performed by the Diagnostic Module - Tank Leakage (DMTL), which is an electrically operated pump fitted to the atmospheric air intake of the EVAP canister.

The test proceeds in 2 stages

1. Reference Leak Measurement - The pump operates against the reference restriction within the DMTL. The Engine Control Module measures the current consumption of the pump motor during this phase.
2. Leak Measurement - The solenoid in the DMTL is operated in order to shut off normal purge airflow into the EVAP canister. The pump can now pressurize the fuel tank and vapor handling system. The Engine Control Module again measures the current consumed by the pump motor and by comparing this with the reference current, determines if a leak is present or not. A high current indicates a tight system and a low current indicates a leaking system.

Fault Conditions That Can Be Identified

1. Reference current high
2. Reference current low
3. Reference leak
4. Noise fault
5. Change over valve stuck open
6. Change over valve stuck closed
7. Rough leak (0.040" or larger)
8. Small leak (0.020" or larger)
9. Pump electrical high
10. Pump electrical low
11. Change over valve electrical high
12. Change over valve electrical low
13. Pump heater high
14. Pump heater low

Scheme 8

Scheme 9

Scheme 10

4.4.1 Description

This diagnostic monitors the long-term adaptions of the fuel system. If these exceed calibrated thresholds for a calibrates time then an appropriate DTC will be recorded.

This monitor operates continuously provided the entry conditions have been met. Any of the components that make up the fuel system that are individually monitored, like the exhaust gas oxygen sensors, fuel pressure sensor and fuel delivery system, must also themselves be in working order with no faults. The general operation of the monitor is shown below.

Scheme 11

Scheme 12

4.6.2 Description

This monitor operates once per drive cycle. It calculates the difference between the measured coolant temperature and an estimated temperature that is derived from a model. When the estimated temperature reaches a calibrated threshold then the error between the two temperatures is accumulated. The model used to calculate the estimated coolant temperature has look-up tables that use a number of engine and vehicle parameters (engine speed, engine airflow, vehicle speed and the difference between intake air and coolant temperature) to derive compensation values. These are added or subtracted from the estimated coolant temperature as appropriate.

An after start counter is also included. The estimated coolant temperature is taken as the measured coolant temperature for a calibrates time following engine start (this time is dependant on the starting coolant temperature) to overcome second order effects which introduce inaccuracy into the estimate of coolant temperature. A normal judgement is made if the measured coolant temperature reaches 80 °C and the accumulated error is not above the failure threshold. A failure judgement is made if the accumulated error equals or exceeds a calibrates fault threshold before the measured coolant temperature reaches 80 °C.

Scheme 13

Scheme 14

4.7.1 Description

If all the entry conditions are satisfied, then the monitor will start execution.

If the actual engine speed more than 100 RPM lower than the target engine speed then a counter is started and once this exceeds the failure time limit a failure judgement is made for idle speed lower than expected.

If the actual engine speed is greater than 200 RPM higher than the target engine speed then a counter is started and once this exceeds the failure time limit a failure judgement is made for idle speed higher than expected.

Scheme 15

4.8.1 Description

The crankshaft sensor is checked for loss of signal during cranking and engine running conditions. When the appropriate entry conditions have been met a loss of sensor pulses for greater than the predefined time will register a fault. If the fault is registered on 2 drive cycles then the MIL will illuminate.

Additionally if the number of crankshaft sensor pulses is incorrect by more than one pulse in any one engine revolution then a fault event is recorded. If the number of fault events exceeds the limit without the engine synchronizing then a crankshaft range performance fault is registered. If the fault is registered on 2 drive cycles then the MIL will illuminate.

Scheme 16

4.9.1 Description

Camshaft position sensors are fitted to both cylinder banks.

The camshaft sensors are checked for loss of signal during cranking and engine running conditions. When the appropriate entry conditions have been met a loss of camshaft sensor pulses for greater than the predefined time will register a fault. If the fault is registered on 2 drive cycles then the MIL will illuminate.

Additionally if a camshaft sensor pulse is not detected between crankshaft sensor missing teeth on more than 4 occasions then a fault event is recorded. If the fault is registered on 2 drive cycles then the MIL will illuminate.

Scheme 17

4.19.1 Description

The ECM supplies are monitored for two conditions.

The first is loss of power when the ignition is on. If the supply is not present for more than a predefined time than a failure will be registered.

The second condition is a system control relay supplying power to the ECM when it should be off. In this case, only a single occurrence of the fault will illuminate the MIL.

Scheme 18

4.20.1 Description

The ECM performs a number of self checks on both the its Random Access Memory (RAM), Read only Memory (RAM) and the two central processor units it uses to control the engine management system. A failure of any of the self-checks will require the ECM to be replaced.

Performing continuous checksum calculations and comparing the results with a stored checksum value checks the ROM. If the calculated checksum and stored checksum do not match then a ROM failure is registered. The DTC logged will depend on when the failure was identified.

A RAM test checks the RAM during ECM initialization and shut down.

The ECM continually monitors itself for illegal internal processor operations, task being performing in the wrong order and attempts to write to the read only memory. When any of these faults are detected, P0606 will be logged.

The ECM uses two processors to perform the its calculations, the two processors are continually communicating with each other to transfer critical information. Internal diagnostic hardware continuously monitors the communication between the two processors for errors. If the level of errors exceeds a defined limit then a failure is registered.

Scheme 19

4.22.1 Description

During ignition on conditions the voltages from the two-track accelerator pedal position sensor is monitored. Both tracks are independently monitored for out of range high and low conditions.

If the input voltage to the ECM stays above a defined value for longer than a calibrates period, the high input failure judgement is made. If the input voltage to the ECM stays below a defined value for longer than a calibrates period, the low input failure judgement is made.

Additionally the signals from the two tracks are compared. If the angle obtained from sensor 1 differs from the angle obtained from sensor 2 by more than a defined amount for longer than a calibration period a range/performance failure judgement is made.

Scheme 20

4.23.1 Description

The Electronic Throttle Interface consists of 2 PWM output drives to control the throttle blade position, with 2 analogue signals for throttle position feedback. The 2 position signals have positive linear characteristics.

Scheme 21

4.24.1 Description

The Engine Torque control is monitored to ensure that there is no large unintended Torque greater than requested by the driver. This monitor consists of an independent engine Torque measurement and engine speed monitor in idle speed control.

Scheme 22

4.25.1 Description

Two checks are performed on the vehicle speed.

The first check is for loss of any of the ABS wheel speed sensor signals. If any of the wheel speed sensor signals are not supplied for longer than the predefined time then a failure is registered

The second check compares the vehicle speed transmitted by the ABS control module and the vehicle speed calculated by the ECM using the data from the transmission output shaft speed sensor. If the transmitted and calculated speed signals do not match for longer than a predefined time then a failure is registered.

Scheme 23

4.26.1 Description

The injector monitor operates on a continuous basis. Open and short detection of each injector is possible by comparing the actual injection signal with a target injection signal. The actual injection signal is derived from a change in injector voltage when the injector is turned off and the target injection signal is derived from an injection set flag.

A normal judgement is made when the injector voltage moves from the on to off position i.e. on the signal edge. If the target signal and the actual signal are both set to one, a normal judgement is made. This process is repeated for each injector in firing order. A failure judgement is made when no injector signal edge is detected i.e. no change in voltage but the injector has been triggered.

Scheme 24

4.27.1 Description

The ignition amplifiers monitor is very similar in operation to the injectors monitor, albeit checking primary coil current instead of voltage.

Internal hardware detection circuits in the ECM, monitor the individual and group outputs to the coil primaries for incorrect current conditions. If a failure is repeatedly noted over a predefined number of engine revolutions then a failure of the appropriate coil or group circuit is registered. If the failure is registered on 2 drive cycles then the MIL will illuminate.

Scheme 25

4.33.1 Description

The engine off timer monitor checks rationality against the behavior of the ECT sensor since the key was turned off.

Scheme 26

4.34.1 Description

The ambient air temperature signal is supplied by the instrument pack. The ECM performs two diagnostic checks on the signal.