Page 362 - Understanding Automotive Electronics

2735 | CH 10 Page 349 Tuesday, March 10, 1998 1:27 PM

DIAGNOSTICS 10

6. With code 76 displayed and the cruise control instrument panel switch
on, depress and release the set/coast button. If the button (switch) is oper-
ating normally, the display advances to 77.
7. With 77 displayed and with the cruise control instrument on, depress and
release the resume/acceleration switch. If the switch is operating normally,
the display advances to 78.
8. With 78 displayed, depress and release the instant/average button on the
MPG panel. If the button is working normally, the code advances to 79.
9. With 79 displayed, depress and release the reset button on the mph panel.
If the reset button is working normally, the code will advance to 80.
10. With 80 displayed, depress and release the rear defogger button on the cli-
mate control head. If the defogger switch is working normally, the code
advances to 70, thereby completing the switch tests.
With code 70 displayed, the engine data can be displayed in sequence by
switching the cruise control instrument panel off. The code should then
advance to 90. To further advance the display, the mechanic must depress the
instant/average button on the MPG panel (to return to the previously displayed
parameter, the mechanic must depress the reset button on the MPG panel). To
exit the engine parameter display mode, the mechanic simultaneously depresses
the Off and Hi buttons on the climate control head. After the last parameter
has been displayed, the code advances to 95.
Figure 10.11 shows the parameter values in sequence. Parameter 01 is the
angular deflection of the throttle in degrees from idle position. Parameter 02 is
the manifold absolute pressure in kilopascals (kPa). The range for this
parameter is 14 to 99, with 14 representing about the maximum manifold
vacuum. Parameter 03 is the absolute atmospheric pressure in kPa. Normal
atmospheric pressure is roughly 90–100 kPa at sea level. Parameter 04 is the
coolant temperature. The conversion from this code to an actual temperature is
given in Table 10.2. Parameter 05 is the manifold air temperature, which uses
the same conversion as parameter 04.
Parameter 06 is the duration of the fuel injector pulse in msec. In reading
this number, the mechanic assumes a decimal point between the two digits (i.e.,
16 is read as 1.6 msec). Refer to Chapters 5, 6, and 7 for an explanation of the
injector pulse widths and the influence of these pulse widths on fuel mixture.
Measurements of aver- Parameter 07 is the average value for the O sensor output voltage.
2
age O sensor voltage are Reference was made earlier in this chapter to the diagnostic use of this parameter.
2
useful for diagnosis of Recall that the O sensor switches between about 0 and 1 volt as the mixture
2
this sensor. oscillates between lean and rich. The displayed value is the time average for this
voltage, which varies with the duty cycle of the mixture. A decimal point should
be assumed at the left of the two digits (i.e., 52 is read as 0.52 volt).
Parameter 08 is the spark advance in degrees before TDC. This value
should agree with that obtained using a timing light or engine analyzer.
Parameter 09 is the number of ignition cycles that have occurred since a trouble

UNDERSTANDING AUTOMOTIVE ELECTRONICS 349