DTC 74

DTC 74: Proportioning Valve System

Proportioning Valve System Circuit:

CIRCUIT OPERATION
The proportioning valve controls the hydraulic pressure to activate the ACD hydraulic multi plate clutch according to signal from the AWD-ECU.

DTC SET CONDITIONS
DTC 74 is set when open circuit or short circuit of the control circuit of the proportioning valve has occurred.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CODE TO BE SET ARE:)
^ Malfunction of proportioning valve
^ Damaged harness and connector
^ Malfunction of the AWD-ECU

DIAGNOSIS
Required Special Tool:
^ MB991958: Scan Tool (M.U.T-III Sub Assembly)
^ MB991824: V.C.I.
^ MB991827: USB Cable
^ MB991911: Main Harness B

STEP 1. Using scan tool MB991958, check data list item 11: Proportioning Valve Current.





CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the LOCK (OFF) position before connecting or disconnecting scan tool MB991958.

1) Connect scan tool MB991958 to the data link connector.
2) Turn the ignition switch to ON position.
3) Actuator test item 05: Check the operation of the ACD.
4) Set scan tool MB991958 to the data reading mode.
^ Item 11: Proportioning Valve Current.
^ While the ACD is operated, value from 50 to 1,000 mA is displayed.

5) Turn the ignition switch to the LOCK (OFF) position.
Q: Is the valve operating properly?
YES: It can be assumed that this malfunction is intermittent.
NO: Go to Step 2.

STEP 2. Measure the resistance at proportioning valve connector B-31.








Disconnect the proportioning valve connector, and measure the resistance between terminal 2 and 3.
^ The resistance should measure less than 4.7 ohms.
Q: Is the measured resistance less than 4.7 ohms?
YES: Go to Step 3.
NO: Replace the hydraulic unit.

STEP 3. Measure the resistance at proportioning valve connector B-31.








Disconnect the proportioning valve connector, and measure the resistance between terminal 2 and ground.
^ The resistance should measure less than 2 ohms.
Q: Is the measured resistance less than 2 ohms?
YES: Go to Step 7.
NO: Go to Step 4.

STEP 4. Check proportioning valve connector B-31 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q: Are the connector and terminals in good condition?
YES: Go to Step 5.
NO: Repair or replace the damaged components.

STEP 5. Check the harness for open circuit between proportioning valve connector B-31 terminal 2 and ground.





Q: Is the harness wire in good condition?
YES: Go to Step 6.
NO: Repair or replace the harness wire.

STEP 6. Using scan tool MB991958, check data list item 11: Proportioning Valve Current.





CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the LOCK (OFF) position before connecting or disconnecting scan tool MB991958.

1) Connect scan tool MB991958 to the data link connector.
2) Turn the ignition switch to ON position.
3) Actuator test item 05: Check the operation of the ACD.
4) Set scan tool MB991958 to the data reading mode.
^ Item 11: Proportioning Valve Current.
^ While the ACD is operated, value from 50 to 1,000 mA is displayed.

5) Turn the ignition switch to the LOCK (OFF) position.
Q: Is the valve operating properly?
YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points -How to Cope with Intermittent Malfunction.
NO: Replace the AWD-ECU

STEP 7. Check proportioning valve connector B-31 and AWD-ECU connector C-139 for loose, corroded or damaged terminals, or terminals pushed back in the connector.








Q: Are the connectors and terminals in good condition?
YES: Go to Step 8.
NO: Repair or replace the damaged components.

STEP 8. Check the harness for open circuit or short circuit to ground between proportioning valve connector B-31 terminal 3 and AWD-ECU connector C-139 terminal 1.








Q: Is the harness wire in good condition?
YES: Go to Step 6.
NO: Repair or replace the harness wire.