DIAGNOSIS
The engine and emission control system in this vehicle are con-
trolled by ECM. ECM has an On-Board Diagnostic system which
detects a malfunction in this system.
When diagnosing troubles, be sure to have full understanding of
the outline of ON-BOARD DIAGNOSTIC SYSTEM and each item
in PRECAUTION IN DIAGNOSING TROUBLE and execute diag-
nosis according to ENGINE DIAGNOSTIC FLOW TABLE in SEC-
TION 6.
ON-BOARD DIAGNOSTIC SYSTEM
ECM performs on-board diagnosis (self-diagnosis) on the system
and operates malfunction indicator lamp as follows.
Malfunction indicator lamp lights when the ignition switch is
turned ON (but the engine at stop) regardless of the condition of
engine and emission control system. This is only to check the
malfunction indicator lamp bulb and its circuit.
If the areas monitored by ECM is free from any trouble after the
engine start (while engine is running), malfunction indicator
lamp turns OFF.
When ECM detects a trouble which has occurred in the areas,it
makes malfunction indicator lamp turn ON while the engine is
running to warn the driver of such occurrence of trouble and at
the same time it stores the exact trouble area in ECM back-up
memory.
PRECAUTIONS IN DIAGNOSING TROUBLES
Before identifying diagnostic trouble code, don’t disconnect cou-
plers from ECM , battery cable from battery, ECM ground wire
harness from engine. Such disconnection will erase memorized
trouble in ECM memory.
Be sure to read PRECAUTIONS FOR ELECTRICAL CIRCUIT
SERVICE in SECTION 0A before inspection and observe what
is written there.
ECM replacement
When substituting a known-good ECM , check for following
conditions. Neglecting this check may cause damage to known-
good ECM .
– Resistance value of all relays, actuators is as specified re-
spectively.
– TP sensor and MAP sensor are in good condition and none
of power circuits of these sensors is shorted to ground.
6E1-10
ENGINE AND EMISSION CONTROL SYSTEM