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DIAGNOSTICS 10

Possible causes for fault code 13 include the following:
• O sensor is not functioning correctly.
2
• Defective connections or leads.
• The control unit is not processing the O sensor signal.
2
Further investigation is required to attempt to isolate the specific problem.
To check the operation of the O sensor, the average value of its output
2
voltage is measured using the electronic engine control system (the procedure
for which is explained later in this chapter). The desired voltage is displayed on
the climate control head in multiples of .01 volt. That is to say, “00’’
corresponds to 0 volts and “99’’ corresponds to 0.99 volts, and so forth.
Using this voltage, the mechanic follows a procedure outlined in Figures
10.5, 10.6, and 10.7. If the voltage is less than 0.37 volt or greater than 0.57
volt, the mechanic is asked to investigate the wiring harness for defects.
If the O sensor voltage is between 0.37 volt and 0.57 volt, tests are
2
performed to determine whether the O sensor or the control unit is faulty. The
2
mechanic must jumper the O sensor leads together at the input to the control
2
unit, simulating a sensor short circuit, and must read the sensor voltage value
using the climate control display. If this voltage is less than 0.05 volt, the
control unit is functioning correctly and the O sensor must be investigated for
2
defects. If the indicated sensor voltage is greater than 0.05 volt, the control unit
is faulty and should be replaced.
When diagnosing a problem, the mechanic might wish to clear a fault
code from the electronic control memory. A good reason to do this, for
example, would be to test whether a failure is “hard’’ or intermittent. To
clear trouble codes (with the system in diagnostic mode), the mechanic
simultaneously pushes the Off and Hi buttons on the climate control head
until “00’’ is displayed. After all fault codes are cleared, code 70 will appear.

Figure 10.5
DFI Oxygen Sensor
Circuit

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 343