Diagnostic Strategies
Diagnostic CodesAll emissions-related diagnostic codes relevant to the Jaguar vehicles are included and detailed.
- The SAE diagnostic codes, which commence with a number "0", e.g. P0234.
- Voluntary codes, which have been added to the system and commence with a number "1", e.g. P1234.
On-Board Diagnostics II
OBD II covers any failure of the powertrain system likely to affect exhaust gas quality; this includes fuel, ignition, transmission, anti-lock braking, active suspension, tire pressure monitoring and active differential failures. The emission effect threshold is an increase of 1.5 times the base vehicle standard.
The OBD II document contains clauses covering standard communication protocols, fault codes, vehicle terminology and vehicle interface points. Whereas the original OBD only monitored failed items, OBD II provides failure prediction by observing performance deterioration over a period of time. The four main areas of observation are catalyst, misfire, exhaust gas recirculation and secondary air system.
Catalyst Monitoring
Precise control of the fuel and air mixture to the correct stoichiometric level is essential to the proper function of the three way catalyst, which oxidizes Carbon Monoxide (CO) and Hydrocarbons (HC), while reducing Nitrous Oxide (NOx).
Deterioration of the catalyst conversion efficiency leads to a higher level of emissions. In order to be able to detect a change in the efficiency of the catalyst, the control system must observe both the incoming and the outgoing exhaust gases. To achieve this aim, exhaust gas oxygen sensors are fitted both upstream and downstream of the catalytic converter.
Misfire Monitoring
As engine misfire is the major cause of damaged catalytic converters, control systems must be able to monitor the quality of each individual firing and so detect engine misfire. The control system must recognize the following three types of engine misfire:
- A misfire which causes instantaneous catalyst damage.
- A misfire which will cause a vehicle to fail a Federal Emissions procedure.
- A misfire which will cause a vehicle to fail an Inspection and Maintenance test.
To create a reference for engine timing, the system needs to accurately detect engine position and speed. This is done by using a Crankshaft Position Sensor (CKPS).
Exhaust Gas Recirculation (EGR) Monitoring
The production of Nitrous Oxide is limited by the EGR system recirculating exhaust gas through the combustion chamber. The introduction of exhaust gas contaminates the fuel and air mixture and causes a slower/cooler fuel burn, reducing Nitrous Oxide emissions.
If the EGR system seizes closed it will cause the uncontrolled production of Nitrous Oxide; if it seizes open it will cause cooler and cooler combustion resulting in high Hydrocarbon and Carbon Monoxide emissions.
Control systems must detect a failure based upon a fixed Nitrous Oxide emission level. To achieve this control a temperature sensor is fitted in the EGR pipe and levels of emission can be assumed from changes in the temperatures recorded for given EGR valve openings.
Secondary Air Injection Monitoring
Secondary air, i.e. air from the secondary injection system is pumped into the exhaust pipe during the first 30 seconds of engine running, coinciding with burning , excess fuel, mixture expelled from the engine. This combination allows the excess fuel to burn, in the exhaust, shortening the raising time of the catalyst operating temperature.
Control systems must indicate when the air flow, from the secondary air injection system, decreases to the extent that an emissions failure level is reached. The system can gauge the air being delivered by recording the drift in oxygen sensor switching levels.
Engine Management System
The engine management system is controlled by the Engine Control Module (ECM) (1), which receives signals from the various EMS sensors, compares them to the required standards and then modifies the fuel and ignition settings to maintain an optimum, stoichiometric, fuel and air mixture under all conditions. Sensor information is supplied to the ECM as inputs (2), and control commands are issued through the ECM outputs (3).
NOTE: Reference numbers eg (1) are shown in figure below.
Engine Management System:
1. Engine Control Module (ECM)
2. Engine Control Module Inputs
3. Engine Control Module Outputs
4. Mass Air Flow Sensor (MAFS)
5. Intake Air Temperature Sensor (IATS)
6. Idle Speed Control Valve (ISCV)
7. Engine Coolant Temperature Sensor (ECTS)
8. Fuel Pump
9. Fuel Rail
10. Fuel Pressure Regulator
11. Fuel Injector (FI)
12. Spark Plugs with Integral Coils
13. Catalytic Convertor
14. Heated Oxygen Sensors and Heaters (HO2S)
15. Throttle Position Sensor (TPS)
16. Exhaust Gas Recirculation (EGR) Valve
17. EGR Function Sensor
18. Knock Sensor (KS)
19. Crankshaft Position Sensor (CKP)
20. Engine Position Sensor (CMP)
21. Secondary Air Injection System (AIR)
22. Mechanical Check Valve
23. Fuel Tank
24. Activated Charcoal Canister
25. Canister Purge Valve
26. Fuel Level Sensor
27. Park Neutral Switch
28. Security and Locking Control Module
29. Ignition On
30. Instrument Pack (Road Speed)
31. Trip Computer
32. Diagnostic MIL Lamp
33. Data Link Connector (DLC)
34. Transmission Control Module (Torque Control)
35. Inertia Switch
Detailed descriptions of the Engine Management Components can be found at their respective locations within the ALLDATA heirarchy.
The park/neutral switch (27), Security and Locking Control Module (SLCM) (28) and ignition on (29), signals are conveyed to the ECM input. Signals are conveyed to the instrument pack (road speed) (30), trip computer (31), diagnostic MIL lamp (32), Data Link Connector (DLC) (33), and Transmission Control Module (TCM) (Torque Control) (34), from the ECM.