The largest and best supported Jaguar cars enthusiast site on the Internet!

Serving Enthusiasts since 1993
The Jag-lovers Web

Currently with 3,166 members

Jag-lovers' Ebooks
- Jag-Lovers' x300 Ebook -

6 - Engine Management & Emissions Control ( )


The engine ECU receives input signals from a number of sensors and uses this information to control the operation of the ignition system, fuel injectors, Idle Speed Control Valve and other sundry equipment.

Any sensor values which appear incorrect or out of range, will set an error code and cause the Check Engine light to come on. The ECU will then set a default value for that sensor and continue to operate as best it can with the information. Although itself commonly suspected to be the source of trouble, problems can almost always be traced back to a failed input sensor or connection.

Diagnostic information is output via the ODBII connector, which can be found as a plug to the right side of the steering column. The codes can be fully interpreted by the Jaguar Diagnostic equipment, but commercially available software using a laptop computer will allow a reasonable level of diagnosis to be undertaken.

In addition to the catalytic converters, cars in the US and some other markets are fitted with Exhaust Gas Recirculation and Air Pump equipment. The Evaporative Emissions system is also fitted in most markets.

The ECU does 'learn' the car over a period of time, but can be fully reset by disconnecting the battery for an hour.

6.1 - MAF - Mass Airflow Meter ( )

The MAF is situated in the intake air ducting between the air filter and inlet manifold. It measures the volume of air entering the engine and is therefore a major input to the ECU's operation. As a result of the low voltage of the output signal, the connectors are gold plated and should always be kept scrupulously clean.

6.10 - Evaporative Emission Control ( )

This system captures fuel vapours from the tank and throttle body which would otherwise be released into the atmosphere. Vapour from the tank is collected via hose in a charcoal canister mounted behind the left front wheel. When the engine is running, the vapour is pulled by inlet vacuum into the throttle body and burnt as part of the normal combustion process. This process is controlled by the ECU to only occur when the engine has warmed up.

6.11 - Traction Control ( )

This system reuses the speed sensors fitted to each wheel for ABS operation to detect if the rear wheels are turning faster than the front, indicating that wheelspin is occurring.

In this case, the system backs off the throttle, reducing engine power until the spin is eliminated. This is done by the motor fitted effectively in line with the throttle cable, on the left side of the engine bay ahead of the coolant plumbing, valves and pump for the internal heater. Operation can be felt through the throttle pedal.

6.2 - Intake Air Temperature ( )

On XJR models this is measured by a sensor built into the base of the supercharger. The sensor decreases in resistance as temperature increases. It has a limited effect on operation, retarding the ignition timing as temperature increases in order to reduce the possibility of pre-ignition.

6.3 - Coolant Temperature ( )

This sensor is on top of the thermostat housing, next to the sensor which drives the temperature gauge, and is one having the locking two pin connector. As with the AIT, it decreases in resistance as temperature increases, but it does have a significant effect on operation, being used to determine cold start and running conditions.

6.4 - Throttle Position Sensor ( )

This is a simple potentiometer attached to the throttle shaft that varies the voltage signal to the ECU dependent on throttle opening. Bad operation or adjustment can result in a high idle speed or hesitation as the ECU is fed misleading information.

6.5 - Crank Position Sensor ( )

This is an electro-magnetic device that understands the crankshaft position by recognising a missing tooth on the crankshaft timing gear. Pulses from the CPS are critical to normal operation as the ECU cannot otherwise determine when the fire the ignition and injectors.

The CPS is mounted on a bracket at the front of the engine, half-way down to the left. It can perhaps be found easiest by identifying the connecting wire and connector leading down the front side of the engine. Replacement is simple, requiring only electrical disconnection and the component to be unbolted from it's bracket.

This component is known to fail at high mileages, and can cause erratic running prior to failure. As a result, some advocate replacement at 80-100K miles as a preventative measure.FS

6.6 - Oxy (Lambda) Sensors ( )

These devices are fitted into the exhaust downpipe and measure the oxygen content of the exhaust gasses. For correct operation it requires operation of an inbuilt heater element and a reference atmosphere, which is obtained from normal air entering along the wiring harness. The device changes resistance dependent on the exhaust gasses and this change is measured by the ECU. Note this is different to earlier models, where the sensor produced a small voltage for the ECU to measure.

European models have two sensors, one in each downpipe. US specification models have four sensors, with the second pair fitted after the catalytic converters to allow the ECU to monitor their effectiveness.

If sensors are removed, ensure each is connected to the correct location and wiring, otherwise the ECU cannot understand the behaviour of the engine and will set a check engine error code.

When the engine is in warm-up, the ECU ignores the sensors and operates using a reference set of information. Once sufficient temperature has been reached, the ECU will begin to use the sensor outputs to control the precise fuel/air mixture of the engine.

In correct operation, probing the voltage with a DVM should show it continuously swinging between 0V and 5V. The component is easy to damage chemically, so do not use solvents such as WD40 to clean the connectors.

The wiring for the sensors is routed to the rear of the engine over the transmission bellhousing, located in place by metal clips. If the oxy sensors appear ineffective, resulting in high CO% readings, check the insulation hasn't frayed at the clips and effectively earthed the sensor.

6.7 - Speed Sensor ( )

This is shared with the speedometer and is mounted in the rear differential unit.

6.8 - Exhaust Gas Recirculation System ( )

This aims to reduce emissions by reducing combustion temperatures in the cylinders. This is done by recirculating exhaust gasses back into the inlet manifold under certain engine conditions, typically part throttle operation, as determined by the ECU.

The EGR pipework leads from the exhaust side, under the exhaust manifold, around to the inlet manifold. On most models, the electrically operated valve is located on the inlet side, but on XJR models it is mounted adjacent to the exhaust manifold itself.

An intake temperature sensor on the intake side near the EGR inlet can detect the correct operation of the system and will set an error code in the ECU if this does not occur. Common causes are failure of the valve itself, or the pipework becoming blocked, particularly at the entry into the inlet manifold.

There has been a recall on '95 - '97 models to overcome blockages by forcing the ECU to periodically operate the valve. However, this has itself caused problems with '95 models and a second recall is being introduced.

6.9 - Air Pump ( )

This is designed to reduce emissions by injecting fresh air into the exhaust gasses to promote their oxidisation. It's operation is controlled by the ECU and it is active only during warm-up, before the Oxy sensor input begins to be used. The pump is driven by an internal motor.


sepbar.jpg (3094 bytes)

This section currently maintained by Pascal Gademer; questions, comments, submissions and suggestions, email


Please help support the move to the new site, and DONATE what you can.
A big Thank You to those who have donated already!



Go to our Homepage
Improve your Jag-lovers experience with the Mozilla FireFox Browser!

  View the latest posts from our Forums via an RSS Feed!

Jag-loversTM Ltd / JagWEBTM 1993 - 2024
All rights reserved. Jag-lovers is supported by JagWEBTM
For Terms of Use and General Rules see our Disclaimer
Use of the Jag-lovers logo or trademark name on sites other than Jag-lovers itself in a manner implying endorsement of commercial activities whatsoever is prohibited. Sections of this Web Site may publish members and visitors comments, opinion and photographs/images - Jag-lovers Ltd does not assume or have any responsibility or any liability for members comments or opinions, nor does it claim ownership or copyright of any material that belongs to the original poster including images. The word 'Jaguar' and the leaping cat device, whether used separately or in combination, are registered trademarks and are the property of Jaguar Cars, England. Some images may also be Jaguar Cars. Mirroring or downloading of this site or the publication of material or any extracts therefrom in original or altered form from these pages onto other sites (including reproduction by any other Jaguar enthusiast sites) without express permission violates Jag-lovers Ltd copyright and is prohibited
Go to our Homepage
Your Browser is: CCBot/2.0 (, IP Address logged as on 21st May 2024 00:29:53