On Board Diagnostics - 5.0L V8: Overview Jaguar XF I

2 Introduction

This document describes the On Board Diagnostic features of the Engine Management System for the naturally aspirated and supercharged versions of the 5.0 litre V8 engine.

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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 (see Table 5 ).

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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 oxygen sensor (d/s HO2S): this process is called dither. At the start of any monitoring period, a short delay will occur before data collection in order to ensure that the fuelling is stable when the diagnosis takes place. If for any reason, the entry conditions become invalid, 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 sufficient period of time, the results are calculated. These are determined by accumulating the locus of the downstream oxygen sensor signal against the accumulation of the upstream oxygen sensor (u/s HO2S), i.e. 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 calibratable threshold then the catalyst diagnostic test has been passed. If the accumulated count equals or exceeds the calibratable threshold then the catalyst system has a problem and the appropriate DTC will be stored.

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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 and/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 drop in acceleration after an anticipated 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 misfire 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. Cylinder 7 (4A) misfire
5. Catalyst damage misfire
6. Low fuel level misfire
7. Cylinder 2 (1B) misfire
8. Cylinder 4 (2B) misfire
9. Cylinder 6 (3B) misfire
10. Cylinder 8 (4B) misfire
11. Excess emissions misfire
12. Random/Multiple cylinder misfire

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

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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 judgements, which are then made on every cylinder firing, irrespective of whether the monitor is enabled or not.

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4.3.2 Description

The evaporative emission monitoring system permits the detection of leaks with a diameter of 0.5 mm (20 thou of an inch) or greater. This is achieved by means of a pressure test of the system, 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 two 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 whether a leak is present. A high current indicates a tight system and a low current indicates a leaking system.

4.4.1 Description

This diagnostic monitors the long-term adaptions of the fuel system. If the adaptions exceed calibrated thresholds for a calibratable 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 and are individually monitored, like the oxygen sensors, fuel pressure sensor and fuel delivery system, must also themselves be in working order with no faults.

4.7.1 Description

The crankcase ventilation valve is incorporated in the right hand cam cover.

Disconnection of the hose that runs between the valve and the intake manifold will result in one of the following

1. The engine will become very unstable at idle with a tendency to stall
2. The OBD system will detect a fuel system fault due to the un-metered air that enters the intake manifold
3. The OBD system will store a specific crankcase ventilation fault code P2279

Fault code P2279 is set if the measured lambda values for both cylinder banks simultaneously indicate an excessively lean condition, when all of the following entry conditions are true

1. More than a pre-determined time has elapsed since engine start
2. The engine speed is below a threshold, or idle speed control is active
3. Closed loop fuel control is active
4. The pre-catalyst Oxygen sensors are active
5. The coolant temperature is within a window
6. The atmospheric pressure is within a window
7. Fuel cut off is not active
8. A pre-determined time has elapsed since fuel cut off was last active
9. The fuel tank level is above a threshold

The hose connected between the left hand cam cover and the clean air duct

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4.8.1 Description

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

Additionally, if the number of crankshaft position 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, a crankshaft position sensor range/performance fault is registered. If the fault is registered on two drive cycles the MIL will illuminate.

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4.9.1 Description

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

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

There is also a crankshaft/camshaft alignment check. The cam adaption valve is compared to the previous trip value. If the difference between the two adaptions differs by more than a calibratable value a fault will be logged and the MIL will illuminate.

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4.10.1 Schematic and Operation

The intake camshafts of the naturally aspirated engine have high lift and low lift modes of operation. This is achieved by providing two sets of cam lobes for each intake valve and splitting the tappets into two sections. Oil pressure operates on a pin in each tappet to engage high lift. The oil is controlled by a separate ECM commanded solenoid valve for each bank of cylinders. The transition from low to high lift happens at approximately 2,400 RPM.

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4.11.1 Description

When starting a cold engine, catalyst light-off times can be improved by generating high engine out energy. The energy is mainly dependent on exhaust temperature and mass flow rate. This is achieved by retarding the ignition timing and increasing engine idle speed as well as adjusting fuel injection and valve timing. Cold Start Monitoring ensures that the intended catalyst light-off times are being achieved. If the intended control is not achieved, then a DTC will be set and the MIL illuminated.

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4.12.1 Description

The monitor will execute when all entry conditions have been satisfied.

The diagnostic functions by monitoring the engine speed. If the actual engine speed is more than 100 RPM below the target engine speed, then a counter is started. Once this counter exceeds the failure time limit a failure judgement is made for idle speed lower than expected. If the actual engine speed is more than 200 RPM above the target engine speed a counter is started. Once this counter exceeds the failure time limit a failure judgement is made for idle speed higher than expected.

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4.16.1 Description

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.

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4.19.1 Description

When all of the entry conditions have been satisfied, the input signals from the four knock sensors (KS) are checked against variable upper and lower threshold levels that are dependent on engine speed. If either sensor input is outside the threshold, then a failure will be flagged. If a failure is noted on two drive cycles the MIL will illuminate.

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4.20.1 Description

The ECM Power Supplies are monitored for the following conditions.

Loss of battery supply when the ignition is on. If the supply is not present for more than a predefined time than a failure will be registered. Aa 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.

Power supply to sensors out of range.

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4.21.1 Description

The ECM performs a number of self checks on both the Random Access Memory (RAM), Read only Memory (ROM) 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 upon 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, tasks being performing in the wrong order and attempts to write to the read only memory. If any of these faults are detected, P0606 will be logged.

The ECM uses two processors to perform 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.

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4.23.1 Description

During ignition on conditions the voltages from the two-track accelerator pedal position sensor are 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 calibratable period, the high input failure judgment is made. If the input voltage to the ECM stays below a defined value for longer than a calibratable period, the low input failure judgment 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 judgment is made.

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4.24.1 Description

The Electronic Throttle Interface consists of two Pulse Width Modulation (PWM) output drives to control the throttle blade position, with two analogue signals for throttle position feedback. The two position signals have positive linear characteristics. There are various diagnostic checks carried out on the throttle control system, all of which result in the illumination of the MIL if a fault is detected. The main checks are described below

With the necessary enabling conditions satisfied

1. The difference between the actual throttle position and the requested position will be compared. If they differ by greater than a calibratable amount a failure judgment will be made.
2. If the throttle blade position PWM is driven at 100% duty for greater than a calibratable period of time a failure judgment will be made.
3. If an over current condition is detected by the throttle driver hardware for greater than a calibratable period of time a failure judgment will be made.
4. If the input voltage to the ECM from either of the position sensors exceeds a defined threshold for greater than a calibratable period of time, a high failure judgment is made.
5. If the input voltage to the ECM from either of the position sensors stays below a defined threshold for greater than a calibratable period of time, a low failure judgment is made.
6. If the difference between the throttle angles reported by the two position sensors differs by greater than a calibratable value a failure judgment is made.

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4.25.1 Description

The Engine Torque is monitored to ensure that there is no large unintended torque available which is greater than that requested by the driver.

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4.26.1 Description

Two checks are performed on the vehicle speed signal. The first check monitors for the loss of any of the ABS wheel speed sensor signals. If any of the signals are not available for greater than a predefined time 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 data from the transmission output shaft speed sensor). If the transmitted and calculated speeds do not match for greater than a predefined time a failure is registered.

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4.27.1 Description

The fuel injector monitor operates continuously. Detection of an open or short circuit condition of each injector is possible by comparing the actual injection signal with a target injection signal. The actual injection signal is derived from the change in injector voltage when the injector is turned off and the target injection signal is derived from an injection set flag.

A normal judgment is made when the injector voltage moves from the on to the 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 judgment is made when no injector signal edge is detected i.e. no change in voltage but the injector has been triggered.

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4.28.1 Description

The ignition amplifier 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 for a predefined number of times then a failure of the appropriate coil or group circuit is registered. If the failure is registered on 2 drive cycles the MIL will illuminate.

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4.32.1 Description

The engine off timer monitor compares the ECM's own internal counter to the change in the engine coolant temperature since the ignition was turned off. If the two differ by more than a calibratable period of time a failure is registered. If the fault occurs on 2 drive cycles the MIL will illuminate.

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4.33.1 Description

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