DC / DC Converter Warning Light Circuit

DESCRIPTION

For models equipped with the N04C engine, 12 V power is used for engine control while the battery voltage is 24 V. Therefore, the DC/DC converter is used to supply 12 V power to the engine control system.
The DC/DC converter has two output circuits. One is the ECD system power source voltage circuit and the other is the ECM memory back-up voltage circuit. ECD system power source voltage is used as the main power source for the ECD system. When the ignition switch in ON position, the ECD system power source voltage circuit supplies 12 V power to the ECD system. ECM memory back-up voltage circuit always supplies 12 V.

ECD system power source voltage is output from terminal 2 or 8. ECM memory back-up voltage is output from terminal 7.

If either terminal 2 or 8 malfunctions, ECD system power source voltage can still be output from the other terminal.
The fail-safe function operates when the DC/DC converter has a malfunction.

During the operation (*2) described in the table below, the DC/DC converter will draw half of the voltage (12 V) from the midpoint between the two batteries connected in series, and supply the voltage to the ECD system.

The DC/DC converter illuminates the DC/DC CONV warning light in the combination meter to inform the driver that the function (*2) described in the table below is operating.

The vehicle can drive normally while the function (*2) described in the table below is operating, but the battery will be under extra load. Therefore, after the fail-safe function operates, be sure to check the battery voltage. If the battery voltage is below the specification, charge or replace the battery Click here.

The DC/DC converter does not have the ability to set and store DTCs.

CAUTION:

Be sure to disconnect the battery terminal before connecting or disconnecting the DC/DC converter connectors. Failure to do so will cause sparks between the terminals, possibly resulting in damage to the connectors.

Note

Do not apply power from the DC/DC converter to systems other than the ECD system via bypassing a wire harness. The DC/DC converter output power is specifically designed for the ECD system. If DC/DC converter power is applied to other systems, the fail-safe function may operate due to overcurrent causing the DC/DC converter to stop functioning.
Keep the DC/DC converter away from water. The DC/DC converter structure is protected from raindrops, but the structure and connectors are not waterproof.
Do not cover the DC/DC converter area because the DC/DC converter generates heat while operating. Covering the DC/DC converter area will obstruct heat released from the DC/DC converter and may result in the converter overheating. If the overheat detection circuit built into the DC/DC converter operates, the DC/DC converter may stop power output if the fail-safe function operates.

Tech Tips

When the DC/DC converter operates normally, the following occurs:

When the ignition switch in ON position, the DC/DC CONV warning light will come on and go off after approximately 1 second.
When the ignition switch in ON position again within 30 seconds after turning the ignition switch in ACC position or off, the DC/DC CONV warning light will come on and go off after approximately 1 second. During this period, the DC/DC converter continues to output ECD system power source voltage.
The ECM memory back-up voltage circuit outputs 12 V no matter what position the ignition switch is in.

The following operations are fail-safe functions.

When fail-safe functions are activated:
Warning Light Condition	Condition	Fail-safe Operations	Fail-safe Deactivation Conditions
OFF	Ignition signal is not received	ECD system power source voltage is below 1 V ECM memory back-up voltage is 8 V or higher	Ignition switch signal is received
OFF	Ground fault (case ground)	ECD system power source voltage is below 1 V ECM memory back-up voltage is below 1 V	Ground circuit is completed
OFF	Voltage input to terminal No. 1 (+24 V) of the DC/DC converter is below 9 V	ECD system power source voltage is below 1 V ECM memory back-up voltage is below 1 V	Voltage input to terminal No. 1 (+24 V) of the DC/DC converter is 9 to 36 V
OFF	Voltage input to terminal No. 1 (+24 V) of the DC/DC converter is 9 to 18 V	ECD system power source voltage is 6 to 14 V ECM memory back-up voltage is 6 to 14 V	Voltage input to terminal No. 1 (+24 V) of the DC/DC converter is 18 to 36 V
OFF	Voltage input to terminal No. 1 (+24 V) of the DC/DC converter is 36 V or higher	ECD system power source voltage is below 1 V ECM memory back-up voltage is 8 V or higher	Voltage input to terminal No. 1 (+24 V) of the DC/DC converter is 18 to 36 V
ON	Voltage input to terminal No. 1 (+24 V) of the DC/DC converter is 18 to 36 V, and current output from terminals No. 2 (OUT1) and No. 8 (OUT2) of the DC/DC converter is 22 A or higher	ECD system power source voltage is below 1 V ECM memory back-up voltage is 8 V or higher	Current output from terminals No. 2 (OUT1) and No. 8 (OUT2) of the DC/DC converter is below 22 A Ignition switch OFF then ON
ON	Current output from terminal No. 7 (OUTM) of the DC/DC converter is 5 A or higher	ECD system power source voltage is 11 to 14 V ECM memory back-up voltage is below 1 V	DC/DC converter replacement (*1)
ON	ECD system power source voltage is 16 V or higher	ECD system power source voltage is 11 to 14 V (*2) ECM memory back-up voltage is 8 V or higher	ECD system power source voltage is below 16 V Ignition switch OFF then ON
ON	Voltage input to terminal No. 1 (+24 V) of the DC/DC converter is 18 to 36 V, and ECD system power source voltage is below 9 V	ECD system power source voltage is below 1 V ECM memory back-up voltage is 8 V or higher	DC/DC converter replacement (*3)
ON	Measured Temperature is too high	ECD system power source voltage is 11 to 14 V (*2) ECM memory back-up voltage is 8 V or higher	Measured temperature is normal
ON	DC/DC converter internal voltage (5 V) is not normal	ECD system power source voltage is 11 to 14 V (*2) ECM memory back-up voltage is 8 V or higher	DC/DC converter internal voltage (5 V) returns to normal Ignition switch OFF then ON

*1: Condition that the overcurrent protection circuit fuse (5 A) in the DC/DC converter is blown

*2: Condition that the DC/DC converter draws half of the voltage (12 V) from the midpoint between the two batteries connected in series, and supplies the voltage to the ECD system

*3: Internal malfunction of the DC/DC converter

WIRING DIAGRAM

System Diagram
Wiring Diagram

INSPECTION PROCEDURE

Note

Before performing electrical work, disconnect the battery negative (-) terminal.
If the battery negative (-) terminal is connected while connecting the DC/DC converter terminal, it may damage the voltage converter, or there may be a fire hazard.

Tech Tips

The circuit that send DC/DC CONV warning light signal to this system is inspected in the voltage converter system Click here.
During inspection for the voltage converter system, if there is an instruction that indicates to go back inspections for each system, proceed to the next step.

PROCEDURE

CHECK HARNESS AND CONNECTOR (COMBINATION METER - DC/DC CONVERTER)

Disconnect the C5 and X17 connectors.

Measure the resistance according to the value(s) in the table below.

Standard resistance

Tester Connection	Condition	Specified Condition
C5-18 (DCDC) - X17-6 (IND)	Always	Below 1 Ω
X17-6 (IND) - Body ground	Always	10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

PROCEED TO NEXT INSPECTION PROCEDURE SHOWN IN PROBLEM SYMPTOMS TABLE

METER / GAUGE SYSTEM DC / DC Converter Warning Light Circuit