3.
Is the problem found?
 | ▶ Repair the trouble causing part and go to "Verification of Vehicle Repair". |
 | ▶ Go to "Power Circuit Inspection". |
Main relay operates when Ignition ON signal is inputted to terminal 28 of ECM CUD-K connector and it supplies power to ECM, fuel pump relay, CMP, EGR actuator, throttle flap actuator, PTC heater relay and brake switch, etc. Especially, the power supplied to ECM is used as a main power of injectors, rail pressure control valve and ECM operation.
When IG KEY ON signal is shut off during turning engine OFF, ECM stops injector operation then engine turns OFF. Approx. after 5 sec., ECM shuts OFF main relay and system turns OFF.
Main relay is very important for engine operation, so careful inspection is strongly required.
When IG KEY OFF signal is imputted to ECM. ECM stops injector operation andn engine turns OFF. Then, After-run(turning off process of ECM intermal system) is performed in order to shut system down. During this process, if main relay power supply is cut too late or power supply is cut too early before After-run process completes, ECM detect main relay error and P0685 is set.
Item | Detecting Condition | Possible Cause | ||
DTC Strategy | ● Voltage monitoring | ● Main relay circuit ● Main relay component | ||
Enable Conditions | ● IG KEY "ON" | |||
Threshold Value | ● When main relay respond to IG KEY - ON/OFF signal too fast or slow (After-run finished and it requires more than 2 sec. for Main relay to be deactivated. Main relay deactivated before After-run finished more than 3 times. ) | |||
Diagnostic Time | ● Immediately | |||
Fail Safe | Fuel Cut | NO | ||
EGR Off | NO | |||
Fuel Limit | NO | |||
Check Lamp | NO | |||
Main Relay Coil Resistance | 73±10 Ω (20℃) |
Fig.1) Main relay operates when IG KEY "ON" (CUD-K terminal 28 ON signal), it turns "OFF" in 12 sec. after IG KEY "OFF".
Electrical systems consist of a lot of harness and connectors, poor connection of terminals can cause various problems and damge of component.
Perform checking procedure as follows.
Check damage of harness and terminals : Check terminals for contact resistance, corrosion and deformation.
Check connecting condition of ECM and component connector : Check terminal seperation, damage of locking device and connecting condition between terminal and wiring.
Disconnect the pin which requires checking at male connector and insert it to the terminal at female connector for checking connecting condition. ( after checking, reconnect the pin at correct position. )
Is the problem found?
| ▶ Repair the trouble causing part and go to "Verification of Vehicle Repair". |
| ▶ Go to "Power Circuit Inspection". |
Check power circuit voltage
IG KEY "OFF", ENGINE "OFF".
Disconnect main relay.
Measure the voltage between power input terminal of main relay connector and chassis ground,.
Measure the voltage between coil power terminal of main relay connector and chassisg ground.
Specification : 11.5V~13.0V
Is the measured voltage within the specification?
| ▶ Go to "Check power supply line(relay→actuator)" as follows. |
| ▶ Repair ECU FUSIBLE LINK in E/R JUNCTION BOX and related circuit and go to "Verification of Vehicle Repair". |
Check power supply line(relay▶actuator)
IG KEY "OFF", ENGINE "OFF".
Disconnect main relay and ECM connector.
Connect 'Power from battery to main relay' terminals(30, 87, and 87a) with power by jump wires.
Measure the voltage on 'Main relay control' terminal and 'Main relay ON input' terminals of ECM harness connector(CUD-K).
Specification : 11.5V~13.0V
Is the measured voltage within the specification?
| ▶ Go to "Control Circuit Inspection". |
| ▶ Check and repair the open circuit where voltage can not be checked and go to "Verification of Vehicle Repair". |
Check open in control circuit
IG KEY "OFF", ENGINE "OFF".
Disconnect main relay and ECM connector.
Check the resistance of main relay control circuit between ECM harness connector and Main relay harness side.
Specification : Continuity ( below 1.0Ω )
Is the measured resistance within the specification?
| ▶ Go to "2. Check short to ground in control circuit" as follows. |
| ▶ Repair open in control circuit and go to "Verification of Vehicle Repair". |
Check short to ground in control circuit
IG KEY "OFF", ENGINE "OFF".
Disconnect main relay and ECM connector.
Check the resistance between main relay control terminal and chassis ground.
Specification : Discontinuity ( Infinite Ω )
Is the measured resistance within the specification?
| ▶ Go to "3.Check short to battery in control circuit" as follows. |
| ▶ Repair short to ground in control circuit and go to "Verification of Vehicle Repair". |
Check short to battery in control circuit
IG KEY "OFF", ENGINE "OFF".
Disconnect main relay and ECM connector.
IG KEY "ON".
Measure the voltage between main relay control terminal and chassis ground.
Specification : 0.0V~0.1V
Is abnormal voltage detected in the circuit with both connectors disconnected?
| ▶ Repair short to battery in signal circuit and go to "Verification of Vehicle Repair". |
| ▶ Go to "Component Inspection". |
Check main relay component resistance
IG KEY "OFF", ENGINE "OFF".
Disconnect main relay.
Measure the resistance between main relay control terminals (Component side).
Specification : 73±10 Ω (20℃)
Is the measured resistance within the specification?
| ▶ Go to "2. Check main relay component operation" as follows. |
| ▶ Replace main relay and go to "Verification of Vehicle Repair". |
Check main relay component operation
IG KEY "OFF", ENGINE "OFF".
Disconnect main relay.
Supplies random B+ and ground to coil sides of main relay. (Component side)
Check continuity between main relay power supply terminals - 30 and 87. (Component side)
Specification : When power is supplied : Continuity ( below 1.0Ω )
When power is not supplied : Discontinuity ( Infinite Ω )
Is the continuity test within the specification?
| ▶ Go to "Verification of Vehicle Repair". |
| ▶ Replace main relay and go to "Verification of Vehicle Repair". |
※ Repeat this process 2~3 times.
After a repair, it is essential to verify that the fault is corrected.
After connecting GDS select "Diagnostic Trouble Codes(DTCs)" mode to and then clear DTC.
Drive the vehicle within DTC Enable conditions in General information.
After selecting "Diagnostic Trouble Codes(DTCs)" mode and check DTC is recorded again.
Are any DTCs recorded ?
| ▶ Go to the DTC guide of recorded NO. in GDS |
| ▶ System operates within specification. |
