4WD Control System Check

NOTE:

Be sure to read "PRECAUTIONS FOR ELECTRICAL CIRCUIT SERVICE : " before circuit inspection and observe what is written there.
For system circuit, refer to the figure of "4WD Control System Circuit" in "4WD CONTROL SYSTEM DESCRIPTION: FRONT - H25 ENGINE MODEL ".
For terminal arrangement, "4WD Control Circuit Voltage Check: Front - H25 Engine Model".

Before performing the trouble diagnosis, check that the transfer and front differential are in good condition and there is no air leakage from air hoses and the actuator. Refer to "4WD CONTROL SYSTEM INSPECTION : " for air leakage.

DIAGNOSTIC PROCEDURE

Step	Action	Yes	No
1	Turn ON ignition switch (but engine at stop) and check malfunction indicator lamp. Does lamp light up?	Go to Step 2.	A trouble has occurred at some place. Repair it referring to "MALFUNCTION INDICATOR LAMP (MIL) CHECK ".
2	Check 4WD switch circuit Turn ignition switch ON and check voltage between terminal "C51-1-11" and terminal "C51-3-26" (ground). Voltage between terminals When transfer shift lever is in "N" or "2H": 10 - 14 V When transfer shift lever is in "4L" or "4H": 0 - 1 V Is the check result satisfactory?	Go to Step 3.	Check 4WD switch referring to "TRANSFER 4WD SWITCH INSPECTION ", and "BLK/ ORN" and "BLK" circuits of 4WD switch. If OK, substitute a known-good ECM (PCM) and recheck.
3	Check power supply Turn ignition switch ON. Check voltage between "C51 -1 -15" and "C51 -3-26" (ground). Voltage between terminals When transfer shift lever is in "N" or "2H": 0 - 1 V When transfer shift lever is in "4L" or "4H": 10 - 14 V Is the check result satisfactory?	Go to Step 4.	Check "RED" circuit. If it is OK, substitute a known-good ECM (PCM) and recheck.
4	Check air pump assembly circuit Check for proper connection to air pump assembly at all terminals. Turn ignition switch ON. Check voltage between "C51-1-18" and "C51 -3-26" (ground). Voltage between terminals When transfer shift lever is in "2H" or "N": 0 - 1 V When transfer shift lever is in "4L" or "4H" (more than 4 seconds after shifted to "4L" or "4H"): 10-14 V Is the check result satisfactory?	Go to Step 5.	Check air pump assembly referring to "AIR PUMP ASSEMBLY INSPECTION: FRONT - H25 ENGINE MODEL ", and then "PNK" circuit. If OK, substitute a known-good ECM (PCM) and recheck.
5	Check 4WD indicator lamp circuit Turn ignition switch ON. Check voltage between "C51 -1 -7" and "C51 -3-26" (ground). Voltage between terminals When transfer shift lever is in "2H" or "N": 10 - 14 V When transfer shift lever is in "4L" or "4H": 0 - 1 V Is the check result satisfactory?	4WD control system is in good condition.	Check "ORN/BLK" circuit (including indicator lamp and combination meter). If OK, substitute a known-good ECM (PCM) and recheck.