TOHATSU BFT250A Service Manual page 127

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SYSTEM DESCRIPTION
SELF-DIAGNOSIS SYSTEM
The ECM has a self-diagnosis function that memorizes
the failure code and turns the MIL ON when it detects
an abnormality with the input/output system.
FAIL-SAFE FUNCTION
The PGM-FI system is provided with a fail-safe function
to provide minimum running capability even when there
is trouble in the system. When any abnormality is
detected by the self-diagnosis function, running
capability is maintained by pre-programed value in the
simulated program map. When any abnormality is
detected in the MAP sensor or CKP sensor, the fail-safe
function stops the engine to protect it from damage.
DTC (Diagnostic Trouble Code)
• The DTC is composed of a main code and a sub
code and it is displayed as a hyphenated number
when retrieved from the ECM with the HDS.
The digits in front of the hyphen are the main code,
they indicate the component of function failure.
The digits behind the hyphen are the sub code, they
detail the specific symptom of the component or
function failure.
For example, in the case of the TP sensor:
– DTC 07 – 1 = (TP sensor voltage) – (lower than
the specified value)
– DTC 07 – 2 = (TP sensor voltage) – (higher than
the specified value).
• The MAP, EBT, TP, and IAT sensor diagnosis will be
made according to the voltage output of the affected
sensor.
If a failure occurs, the ECM determines the Function
Failure, compares the sensor voltage output to the
standard value, and then outputs the corresponding
DTC to the HDS.
For example:
– If the input voltage line (A) on the MAP sensor is
opened, the ECM detects the output voltage is
about 5 V, then the DTC 3-2 (MAP sensor circuit
high voltage) will be displayed.
– If the input voltage line (B) on the TP sensor is
opened, the ECM detects the output voltage is 0
V, then the DTC 7-1 (TP sensor circuit low
voltage) will be displayed.
MAP SENSOR
EBT SENSOR
5 V
5 V
OUTPUT
(A)
VOLTAGE
5 V
OUTPUT
VOLTAGE
TP SENSOR
(B)
IAT SENSOR
FUEL SYSTEM
5 V
OUTPUT
VOLTAGE
5 V
OUTPUT
VOLTAGE
5-5