Trip Computer - Notes to Assist in Fault Diagnosis
83jaguar01Date 09-01-83
ITEM: J83/53
SUBJECT: TRIP COMPUTER MALFUNCTIONS
MODEL: XJ6 & XJ-S
The following notes are to assist in fault diagnosis:
a) Symptom - (on trip computer)
With vehicle in motion, the trip computer display shows inaccurate or zero figures on the following functions:- "INST" "AVE" "DIST" "AV SPD".
Symptom - (on trip computer analyzer, P/N 60973069)
Computer input checks show no flashing DISTANCE LED'S on test 4.
Cause
Problem may be caused by faulty speedometer although speed readings and odometer continue to work normally.
Diagnosis
Use a voltmeter with probes placed between the yellow trip computer input lead and a suitable ground. When vehicle is moved forward inch by inch, voltage readings should move up and down between 1 volt and 7 volts. (Max/min voltage should be measured with vehicle stationary.) If the voltage readings vary significantly from the figures quoted, check speedometer by substitution.
b) Symptom - (on trip computer)
With vehicle in motion, the trip computer display shows high fuel usage on "FUEL" function and correspondingly low mpg figures on "INST" and "AVE" functions. With vehicle stationary, ignition "on" but engine "off", the trip computer display on "FUEL" continues to advance.
Symptom - (on trip computer analyzer, PIN 60973069)
Computer input checks show flashing FUEL LED'S on test 2.
Cause
Problem may be caused by an open circuit, yellow/green lead between the 7EM computer interface and pin 26 of the ECU, or faulty interface unit.
Diagnosis
Remove plug connectors from interface and ECU units (both located on rear bulkhead in trunk). Confirm open circuit condition by performing continuity check between appropriate terminations in plug connectors (see diagram). If open circuit confirmed, locate and correct.
(Note: There is an in-line bullet connector in the yellow/green lead located in righthand corner of trunk where the small harness is tied to main harness).
If no open circuit condition, test interface by substitution.
c) Dealers are reminded to check the position of the "mls km" switch. Misleading trip computer readings will be obtained on all functions except "TIME" if switch is in "km" position.
d) Symptom - (on vehicle)
Trip computer shows 999 on "DIST" function, with tenths digits rotating 0 through 9 with added mileage.
Diagnosis
This is perfectly normal operation and only requires depression of the "RESET" button.