ENGINE GENERAL INFORMATION AND DIAGNOSIS (H25 ENGINE) 6-1-127
SYSTEM DESCRIPTION
Refer to “Air Intake System Description” in Section 6E2.
DTC DETECTING CONDITION AND TROUBLE AREA
DTC CONFIRMATION PROCEDURE
1) With ignition switch OFF, connect scan tool.
2) Turn ON ignition switch and clear DTC by using scan tool if any.
3) Start engine and warm up to normal operating temperature.
4) Run engine at idle speed for 30 sec.
5) Check DTC and pending DTC by using scan tool.
DTC TROUBLESHOOTING
DTC DETECTING CONDITION TROUBLE AREA
Idle engine speed is lower than desired engine speed
100 r/min. though IAC valve opening is about 100%.
Idle engine speed is higher than desired engine speed
200 r/min. though IAC valve opening is about 0%.
IAC valve monitor voltage is high.
IAC valve or its circuit
Air intake system
VSS
Engine mechanical
External load
ECM (PCM)
NOTE:
Check to make sure that following conditions are satisfied when using this DTC CONFIRMATION PRO-
CEDURE.
• Intake air temperature : between –14°C and 70°C (6.8°F and 158°F)
• Atmospheric pressure : higher than 560 mmHg (Altitude : lower than 2790 m (9150 ft))
Step Action Yes No
1Was “Engine Diag. Flow Table” performed? Go to Step 2. Go to “Engine Diag. Flow
Ta bl e ”.
2 Idle Speed check :
1) Check idle speed and idle air control duty
referring to “Idle Speed/Idle Air Control
(IAC) Duty Inspection” in Section 6E2.
Are they in good condition?
Intermittent trouble.
If OK, substitute a known-
good ECM (PCM) and
recheck.
Go to Step 3.
3 IAC Valve inspection :
1) Inspect IAC valve referring to “Idle Air Con-
trol Valve (IAC valve)” in Section 6E2.
Is it in good condition?
Go to Step 6. Go to Step 4.
4 IAC Valve Circuit check :
1) With ignition switch OFF, disconnect ECM
(PCM) couplers.
2) Check resistance between C51-2-14 and
C51-2-15, C51-2-24 and C51-2-25.
Is each resistance 40 – 48
Ω
?
Go to Step 5. Faulty “LT GRN/BLK”,
“PPL/BLK”, “GRY/BLU” or
“PPL/YEL” wire.
If OK, faulty IAC valve.
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