DTC 12

DIAGNOSTIC TROUBLE CODE PROCEDURES
DTC 12: Power Supply Voltage (Valve Power Supply) System

Power Supply Circuit:

CIRCUIT OPERATION
The AWD-ECU (terminal 13) is energized through the fuse by the ignition switch.

DTC SET CONDITIONS
The power supply circuit open or short circuit if the power supply voltage of the AWD-ECU is below 9 volts or above 18 volts. Or DTC 12 is set when the battery voltage drops.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CODE TO BE SET ARE:)
^ Malfunction of the battery
^ 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. Check the battery.
Q: Is the battery damaged?
YES: Charge or replace the battery.
NO: Go to Step 2.

STEP 2. Using scan tool MB991958, check data list item 10: Battery Voltage.





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) Set scan tool MB991958 to the data reading mode.
^ Item 10: Battery Voltage.
^ The voltage should equal battery positive voltage.

4) Turn the ignition switch to the LOCK (OFF) position.
Q: Is the measured voltage battery positive voltage?
YES: It can be assumed that this malfunction is intermittent.
NO: Go to Step 3.

STEP 3. Measure the power supply voltage at AWD-ECU connector C-139 by backprobing.








1) Turn the ignition switch to the ON position.
2) Measure the voltage between AWD-ECU connector C-139 terminal 13 and ground by backprobing.
^ The voltage should measure battery positive voltage.

3) Turn the ignition switch to the Lock (OFF) position.
Q: Is the measured voltage battery positive voltage?
YES: Go to Step 7.
NO: Go to Step 4.

STEP 4. Check intermediate connector C-124, AWD-ECU connector C-139, junction block connector C-210 and C-211 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 5.
NO: Repair or replace the damaged components.

STEP 5. Check the harness for open circuit or short circuit to ground between the ignition switch and the AWD-ECU connector C-139 terminal 13.





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 10: Battery Voltage.





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) Set scan tool MB991958 to the data reading mode.
^ Item 10: Battery Voltage.
^ The voltage should equal battery positive voltage.

4) Turn the ignition switch to the LOCK (OFF) position.
Q: Is the measured voltage battery positive voltage?
YES: It can be assumed that this malfunction is intermittent.
NO: Replace the AWD-ECU

STEP 7. Check AWD-ECU connector C-139 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 6.
NO: Repair or replace the damaged components.