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DTC P1603: Battery Backup Circuit Malfunction
 
 
 
 
TECHNICAL DESCRIPTION
  • The ECM checks the open circuit of battery backup line.
noteWhen the system detects an open circuit in the battery backup line, it makes 1 failure judgment of other diagnostic trouble codes (DTCs).
 
 
DESCRIPTIONS OF MONITOR METHODS
  • Battery backup line voltage is under specified value.
 
 
MONITOR EXECUTION
  • Continuous
 
 
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
  • Not applicable
Sensor (The sensor below is determined to be normal)
  • Not applicable
 
 
DTC SET CONDITIONS
Logic Flow Chart
 
 
Check Conditions
  • Engine starting sequence was completed.
  • Battery positive voltage is more than 10 volts.
Judgment Criterion
  • Battery backup line voltage is less than 6 volts for 2 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • All diagnostic trouble codes are set once failure judgment is completed.
 
 
OBD-II DRIVE CYCLE PATTERN
  • None.
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Open or shorted battery backup line, harness damage or connector damage.
  • ECM failed.

 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite main harness A
  • MB992747: V.C.I.-Lite USB cable short
  • MB992748: V.C.I.-Lite USB cable long
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: Vehicles Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
STEP 1. Using scan tool (M.U.T.-III), read the diagnostic trouble code (DTC).
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
(1) Connect scan tool (M.U.T.-III). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-III) .
(2) Turn the ignition switch to the "ON" position.
(3) Erase the DTC.
(4) Start the engine and run it at idle.
(5) Read the DTC.
(6) Turn the ignition switch to the "LOCK" (OFF) position.
Is DTC P1603 set?
Go to Step 2.
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
 
STEP 2. Measure the power supply voltage at ECM connector by backprobing.
(1) Do not disconnect the connector.
(2) Measure the voltage between terminal BACK line and ground by backprobing.
  • Voltage should be battery positive voltage.
Is battery positive voltage (approximately 12 volts) present?
Replace the ECM (Refer to, Removal and Installation ). Then go to Step 4.
Go to Step 3.
 
STEP 3. Measure the power supply voltage at ECM harness side connector.
(1) Disconnect the connector and measure at the harness side.
(2) Measure the voltage between terminal BACK line and ground.
  • Voltage should be battery positive voltage.
Is battery positive voltage (approximately 12 volts) present?
Repair or replace the connector(s), or check and repair the harness of damage in BACK line between battery and ECM connector. Then go to Step 4.
Repair or replace the connector(s), or check and repair the harness of open circuit and short to ground in BACK line between battery and ECM connector. Then go to Step 4.
 
STEP 4. Using scan tool (M.U.T.-III), read the diagnostic trouble code (DTC).
(1) Turn the ignition switch to the "ON" position.
(2) After the DTC has been deleted, read the DTC again.
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is DTC P1603 set?
Retry the troubleshooting.
The inspection is complete.