Introduction to Fuel, Emission Control and Engine Management
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.