DIAGNOSIS
The engine and emission control system in this vehicle are con-
trolled by ECM (PCM). ECM (PCM) 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 (PCM) 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 (PCM) is free from any trouble
after the engine start (while engine is running), malfunction indi-
cator lamp turns OFF.
When ECM (PCM) detects a trouble which has occurred in the
areas,it makes malfunction indicator lamp turn ON while the en-
gine is running to warn the driver of such occurrence of trouble
and at the same time it stores the exact trouble area in ECM
(PCM) back-up memory.
PRECAUTIONS IN DIAGNOSING TROUBLES
Before identifying diagnostic trouble code, don’t disconnect cou-
plers from ECM (PCM) , battery cable from battery, ECM (PCM)
ground wire harness from engine. Such disconnection will erase
memorized trouble in ECM (PCM) memory.
Be sure to read PRECAUTIONS FOR ELECTRICAL CIRCUIT
SERVICE in SECTION 0A before inspection and observe what
is written there.
ECM (PCM) replacement
When substituting a known-good ECM (PCM) , check for follow-
ing conditions. Neglecting this check may cause damage to
known-good ECM (PCM) .
– 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.
ENGINE AND EMISSION CONTROL SYSTEM
6E1-9
SH410