AUTOMATIC TRANSMISSION (DIAGNOSTICS)(4AT) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)
DTC DETECTING CONDITION:
Brake switch malfunction, open input signal circuit
TROUBLE SYMPTOM:
• Gear is not shifted down when driving a down hill.
• Neutral control does not operate.
WIRING DIAGRAM:
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Does the DTC of CAN communication appear in the on-board diagnostics test mode?
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Perform the diagnosis according to the DTC.
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2.CHECK BODY INTEGRATED UNIT.
1) Turn the ignition switch to OFF.
2) Connect the Subaru Select Monitor to the data link connector.
3) Turn the ignition switch to ON.
4) Run the Subaru Select Monitor.
5) Read the data of “Stop Light Switch” using Subaru Select Monitor. 
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3.CHECK TCM.
Read the data of “Stop Light Switch” using Subaru Select Monitor.
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A temporary poor contact of connector or harness may be the cause. Check the poor contact.
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Replace the TCM.
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4.CHECK BODY INTEGRATED UNIT INPUT SIGNAL.
1) Disconnect the harness connector of body integrated unit.
2) Measure the voltage of harness between body integrated unit and stop light switch.
Connector & terminal
(B280) No. 2 (+) — Chassis ground (−):
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Is the voltage 10 V or more?
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5.CHECK STOP LIGHT SWITCH.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from stop light switch.
3) Measure the resistance of harness between stop light switch connectors.
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Is the resistance 1 MΩ or more?
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Replace the stop light switch.
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6.CHECK HARNESS CONNECTOR BETWEEN BODY INTEGRATED UNIT AND STOP LIGHT SWITCH.
1) Turn the ignition switch to ON.
2) Measure the voltage of harness between the body integrated unit and chassis ground.
Connector & terminal
(B280) No. 2 (+) — Chassis ground (−):
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Is the voltage less than 1 V?
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Repair the short circuit of harness between TCM and stop light switch.
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Is there poor contact in input signal of brake switch?
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Check the body integrated unit.
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