Mazda 626 Station Wagon, Workshop Manual

Page: 168 / 577

TROUBLESHOOTING
Finding unusual signals
While referring to the DTC inspection section of the
on-board diagnostic system, use the PID/DATA
MONITOR AND RECORD function to inspect the
input signal system relating to the problem.
1. Turn the ignition on and idle the vehicle. You can
assume that any signals that are out of
specifications by a wide margin are unusual.
2. When recreating the problem, any sudden change
in monitor input signals that is not consciously
created by the driver can be judged as unusual.
Locating the source of unusual signals
Caution
• Com pare the NGS monitor voltage with the
m easurem ent voltage using the DIGITAL
M EASUREM ENT SYSTEM function. If you
use another tester, misreading may occur.
• W hen measuring voltage, attach the tester
ground to the G N D of the PCM that is being
tested, or to the engine Itself. If this is not
done, the m easured voltage and actual
voltage m ay differ.
• A fter connecting th e pin to a waterproof
coupler, confirm ing continuity and
m easuring the voltage, inspect the
w aterproof connector for cracks. If there
are any, use sealant to fix them . Failure to
do this may result in deterioration of the
harness or term inal from w ater damage,
leading to problem s with the vehicle.
Variable resistance type 1 (Throttle position (TP)
sensor)
PCM
Investigate the input signal system
1. When you get an unusual signal, measure the #1
PCM terminal voltage.
• If the #1 terminal voltage and the NGS monitor
voltage are the same, proceed to the next
step.
• If there is a difference of 0.5V or more, inspect
the following points concerning the PCM
connector.
— Female terminal opening looseness
— Coupler (pin holder) damage
— Pin discoloration (blackness)
— Harness/pin crimp is loose or
disconnected.
2. W hen you get an unusual signal, m easure the #2
sensor terminal voltage.
• If there is a 0.5V or more difference between
the sensor and
NGS
voltages, inspect the
harness for open or short circuits.
• If the sensor and
NGS
voltages are the same,
inspect the following points concerning the
sensor connector. If there are no problems,
proceed to next investigation below.
— Female term inal opening looseness
— Coupler (pin holder) damage
— Pin discoloration (blackness)
— Harness/pin crimp is loose or
disconnected.
Investigate the standard power supply system
1. Confirm that the #3 term inal is at 5V.
• If the measured voltage on the #3 terminal is
5V, inspect the following points on the sensor
connector. If there is no problem, proceed to
next investigation below.
— Female term inal opening looseness
— Coupler (pin holder) damage
— Pin discoloration (blackness)
• If the #3 terminal m easures other than 5V,
inspect for the following.
— Open or short circuit in harness
— Harness/pin crimp is loose or
disconnected.
Investigate the
GND
system
1. Confirm that term inal sensor #5 is at 0V.
• If it is at 0V, inspect for the sensor. If
necessary, replace the sensor.
• If not, inspect fo r the following.
— Open or short circuit in harness
— Female terminal opening looseness
— Coupler (pin holder) damage
— Pin discoloration (blackness)
— Harness/pin crim p is loose or
disconnected.
Variable resistance type
2
(Fuel tank level and
mass air flow (MAF) sensors)
F1-147