DTC U0028:87 [START STOP UNIT]

id0902p6023900

System malfunction location

Communication error with rear body control module (RBCM)

Detection condition

•  Start stop unit detects communication error with rear body control module (RBCM) 10 times continuously.

Fail-safe

—

Possible cause

•  Rear body control module (RBCM) connector or terminal malfunction

•  Start stop unit connector or terminal malfunction

•  Short to ground in wiring harness between start stop unit terminal 1Q and rear body control module (RBCM) terminal 3B

•  Open circuit in wiring harness between start stop unit terminal 1Q and rear body control module (RBCM) terminal 3B

•  Rear body control module (RBCM) malfunction

•  Start stop unit malfunction

System malfunction location	Communication error with rear body control module (RBCM)
Detection condition	• Start stop unit detects communication error with rear body control module (RBCM) 10 times continuously.
Fail-safe	—
Possible cause	• Rear body control module (RBCM) connector or terminal malfunction • Start stop unit connector or terminal malfunction • Short to ground in wiring harness between start stop unit terminal 1Q and rear body control module (RBCM) terminal 3B • Open circuit in wiring harness between start stop unit terminal 1Q and rear body control module (RBCM) terminal 3B • Rear body control module (RBCM) malfunction • Start stop unit malfunction

Diagnostic Procedure

Step	Inspection		Action
1	INSPECT REAR BODY CONTROL MODULE (RBCM) CONNECTOR CONDITION • Switch the ignition to off. • Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5].) (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5 (WITHOUT i-stop)].) (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-D 2.2].) • Disconnect the rear body control module (RBCM) connector. • Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection. • Is the connector normal?	Yes	Go to the next step.
1		No	Repair or replace the connector, then go to Step 6.
2	INSPECT START STOP UNIT CONNECTOR CONDITION • Disconnect the start stop unit connector. • Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection. • Is the connector normal?	Yes	Go to the next step.
2		No	Repair or replace the connector, then go to Step 6.
3	INSPECT REAR BODY CONTROL MODULE (RBCM) CIRCUIT FOR SHORT TO GROUND • Verify that the rear body control module (RBCM) connector and start stop unit connector are disconnected. • Inspect for continuity between rear body control module (RBCM) terminal 3B (vehicle wiring harness side) and body ground. • Is there continuity?	Yes	Repair or replace the wiring harness which is shorted to ground, then go to Step 6.
3		No	Go to the next step.
4	INSPECT REAR BODY CONTROL MODULE (RBCM) CIRCUIT FOR OPEN CIRCUIT • Verify that the rear body control module (RBCM) connector and start stop unit connector are disconnected. • Inspect the wiring harness for an open circuit between start stop unit terminal 1Q (vehicle wiring harness side) and rear body control module (RBCM) terminal 3B (vehicle wiring harness side). • Is there continuity?	Yes	Go to the next step.
4		No	Repair or replace the wiring harness which has an open circuit, then go to Step 6.
5	INSPECT REAR BODY CONTROL MODULE (RBCM) • Inspect the rear body control module (RBCM). (See REAR BODY CONTROL MODULE (RBCM) INSPECTION.) • Is the rear body control module (RBCM) normal?	Yes	Go to the next step.
5		No	Replace the rear body control module (RBCM), then go to the next step. (See REAR BODY CONTROL MODULE (RBCM) REMOVAL/INSTALLATION.)
6	VERIFY THAT REPAIRS HAVE BEEN COMPLETED • Reconnect all the disconnected connectors. • Reconnect the disconnected negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5].) (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5 (WITHOUT i-stop)].) (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-D 2.2].) • Clear DTC for the start stop unit using the M-MDS. (See CLEARING DTC [START STOP UNIT].) • Perform the DTC inspection for the start stop unit using the M-MDS. (See DTC INSPECTION [START STOP UNIT].) • Is DTC U0028:87 displayed?	Yes	Repeat the inspection from Step 1. • If the malfunction recurs, replace the start stop unit, then go to the next step. (See START STOP UNIT REMOVAL/INSTALLATION.)
6		No	Go to the next step.
7	VERIFY IF OTHER DTCs DISPLAYED • Are any other DTCs displayed?	Yes	Repair the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [START STOP UNIT].)
7		No	DTC troubleshooting completed.