Trip Computer - Operation
413-01DATE
8/98
V8 XJ Series/XK8
MODEL
1997 MY-ON XK8 Range
1998 MY-ON V8 XJ Series
VIN
001001-ON
812256-ON
Trip Computer Operation - Additional Information
Issue:
Feedback from various surveys suggests that some customers do not fully appreciate certain aspects of operation of the trip computer system and may, as a result, raise unnecessary concerns. This bulletin provides a more technical explanation of trip computer features than the details contained in the Drivers Handbook.
Action:
Be aware of the following points:
1. The indications displayed by the trip computer, especially fuel consumption and predicted range, may appear low if observed over a short distance immediately after resetting of the trip computer memory. This is particularly the case when the first few miles/kilometers following trip resetting are urban driving, where fuel consumption will inevitably be higher due to stop/start driving conditions with frequent acceleration and braking. Poor weather or road conditions which restrict driving to the lower gears will also have an negative effect on fuel consumption.
2. When the initial miles under urban conditions are followed by a period of uninterrupted open-road cruising with reduced braking and gear changing, the figures displayed will be more representative of the vehicle's actual performance. It must be appreciated that the majority of the data displayed to the driver is an average figure since the point of the last reset of the memory, and that short4erm indications may be particularly misleading.
3. "Best possible" indications of fuel consumption and range will occur where the trip computer is reset immediately before a trip under open-road cruising conditions, beginning with the fuel tank full.
4. Customers may not be aware that the trip computer contains two memories. This feature permits the separate recording of, for example, business and leisure trips. The memories are designated "A" and "B". Selection of data entry, data display or resetting of either memory is done using the toggle-action switch labelled A/B, in the facia-mounted Trip Computer Switchpack.
Alternatively, memory "A" could be used to store long-term information of all trips (up to a maximum of 9999.9 miles (16090 km) when automatic reset occurs), while memory "B" could be reset at the start of a particular trip to record the statistics for that trip alone. Examples are shown in U.S. units, and in Metric units.
5. When the ignition is in ON (position II) the following data is being constantly updated into both memories:
Time Distance Covered Fuel Consumed
This allows each memory to calculate independently the values of:
Average Speed Trip distance
Average Fuel Consumption Current Fuel Consumption
Data is displayed from whichever memory is currently selected, and the display shows the average figure since the last reset of the memory selected.
6. "RANGE" and "CURRENT FUEL USAGE" are calculated continuously by the computer system when the vehicle is running, and are thus available for display when selected. This information is not stored within either memory, and cannot be reset. Since this information is available to either display continuously, is not prefixed with either A or B.
7. CURRENT FUEL CONSUMPTION is computed from the amount of fuel consumed by the engine during the last 3 seconds. It is thus to be expected as normal that a display of a poor fuel consumption will accompany or immediately follow a period of harsh acceleration or while ascending a steep incline; within a few seconds a very different fuel consumption (very considerably better than the average fuel consumption) may be indicated, should the vehicle now be descending a steep incline with the throttle closed, with virtually zero fuel being consumed.
8. To reset either memory:
a. With ignition ON (position II) press the Trip Function button (at tip of the lighting/direction indicator switch on the steering column) to cycle through all message center displays until a computer function is selected. Note that resetting can not be completed should RANGE or CURRENT FUEL USAGE be displayed.
b. Select the memory required, using the A/B switch on the Trip Computer Switchpack.
c. Press the 000 button; hold for 3 seconds
The display will then indicate: A:TRIP RESET (assuming A selected)
followed by: A:0.0
d. Trip reset (memory A) is now complete.
9. The trip computer system operates independently of the odometer, which indicates the total distance covered by the vehicle to date, and which can not be reset.
EXAMPLE USING U.S. UNITS
The tables show a hypothetical example. In Table 1, memory A has accumulated data over 1800 miles of driving, since it was last reset. The majority of this mileage was in slow city traffic. However, at a trip odometer reading of 1360 in memory A, memory B was reset prior to some highway driving for the next 440 miles. Memory A was not reset. The analysis of Table 1 then shows the data available for both displays at a trip odometer reading of 1800 miles in memory A.
At this point, (trip odometer reading in memory A of 1800 miles) memory B was again reset, prior to a series of highway driving, covering 400 miles completed in 7.0 hours, as shown in Table 2. Memory A was not reset, so continued to accumulate data for the same trips, in addition to the previous trips. Because the data available for display is the average since the last reset, the additional 400 miles has had little effect on the average speed and miles per gallon figures in Table 2, memory A, compared with the display data for the same input data recorded in memory B for the recent faster highway driving.
EXAMPLE USING METRIC UNITS
The tables show a hypothetical example. In Table 3, memory A has accumulated data over 2900 kilometers of driving, since it was last reset. The majority of this mileage was in slow city traffic. However, at a trip odometer reading of 2190 in memory A, memory B was reset prior to some faster highway driving. The analysis of Table 3 then shows the data available for both displays at a trip odometer reading of 2900 kilometers in memory A.
At this point, (trip odometer reading of 2900 kms in memory A) memory B was again reset, prior to a series of highway driving covering 620 kms, completed in 7.0 hours, as shown in Table 4. Memory A was not reset, so continued to accumulate data for the same trips, in addition to the previous trips. Because the data available for display is the average since the last reset, the additional 620 kms has had little effect on the average speed and fuel consumption figures in Table 4, memory A, compared with the display data for the same input data recorded in memory B for the recent highway driving.