Diagnostic Procedure

WARNING: This page is about a different car, the 2016 Mazda CX-5. However, it is still accessible from the selected car via links, so may be relevant.

Step	Inspection		Action
1	VERIFY REAR BODY CONTROL MODULE (FBCM) DTCs AGAIN Clear the DTC for the rear body control module (RBCM) using the M-MDS. (See CLEARING DTC [REAR BODY CONTROL MODULE (RBCM)] .) Depress the brake pedal. Retrieve the rear body control module (RBCM) DTCs using the M-MDS. (See DTC INSPECTION [REAR BODY CONTROL MODULE (RBCM)] .) Is the same DTC displayed?	Yes	Go to the next step.
1		No	Go to Step 13.
2	INSPECT BRAKE LIGHT BULB (LH) Inspect the brake light bulb (LH). Is the brake light bulb (LH) normal?	Yes	Go to the next step.
2		No	Replace the brake light bulb (LH), then go to Step 13.
3	INSPECT BRAKE LIGHT BULB (RH) Inspect the brake light bulb (RH). Is the brake light bulb (RH) normal?	Yes	Go to the next step.
3		No	Replace the brake light bulb (RH), then go to Step 13.
4	INSPECT HIGH-MOUNT BRAKE LIGHT CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5] .) Disconnect the high-mount brake light 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.
4		No	Repair or replace the connector, then go to Step 13.
5	INSPECT BRAKE LIGHT (LH) CONNECTOR CONDITION Disconnect the brake light (LH) 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.
5		No	Repair or replace the connector, then go to Step 13.
6	INSPECT BRAKE LIGHT (RH) CONNECTOR CONDITION Disconnect the brake light (RH) 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.
6		No	Repair or replace the connector, then go to Step 13.
7	INSPECT REAR BODY CONTROL MODULE (RBCM) CONNECTOR CONDITION 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.
7		No	Repair or replace the connector, then go to Step 13.
8	INSPECT FOR SHORT TO GROUND IN BRAKE LIGHT CIRCUIT Verify that the high-mount brake light, brake light (LH), brake light (RH) and rear body control module (RBCM) connectors are disconnected. Inspect for continuity between rear body control module (RBCM) terminal 4D (wiring harness-side) and body ground. Is there continuity?	Yes	Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: Rear body control module (RBCM) terminal 4D-Brake light (LH) terminal B Rear body control module (RBCM) terminal 4D-Brake light (RH) terminal B Rear body control module (RBCM) terminal 4D-High-mount brake light terminal A If there is a common connector: Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for a short to ground. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has a short to ground. Go to Step 13.
8		No	Go to the next step.
9	INSPECT FOR SHORT TO POWER SUPPLY IN BRAKE LIGHT CIRCUIT Verify that the high-mount brake light, brake light (LH), brake light (RH) and rear body control module (RBCM) connectors are disconnected. Reconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5] .) Switch the ignition ON (engine off or on). Measure the voltage at the rear body control module (RBCM) terminal 4D (wiring harness-side). Is the voltage 0 V ?	Yes	Go to the next step.
9		No	Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: Rear body control module (RBCM) terminal 4D-Brake light (LH) terminal B Rear body control module (RBCM) terminal 4D-Brake light (RH) terminal B Rear body control module (RBCM) terminal 4D-High-mount brake light terminal A If there is a common connector: Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for a short to power supply. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has a short to power supply. Go to Step 13.
10	INSPECT FOR OPEN CIRCUIT IN BRAKE LIGHT CIRCUIT Verify that the high-mount brake light, brake light (LH), brake light (RH) and rear body control module (RBCM) connectors are disconnected. Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5] .) Inspect for continuity between the following terminals (wiring harness-side): Rear body control module (RBCM) terminal 4D-Brake light (LH) terminal B Rear body control module (RBCM) terminal 4D-Brake light (RH) terminal B Rear body control module (RBCM) terminal 4D-High-mount brake light terminal A Is there continuity?	Yes	Go to the next step.
10		No	Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: Rear body control module (RBCM) terminal 4D-Brake light (LH) terminal B Rear body control module (RBCM) terminal 4D-Brake light (RH) terminal B Rear body control module (RBCM) terminal 4D-High-mount brake light terminal A If there is a common connector: Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for an open circuit. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has an open circuit. Go to Step 13.
11	INSPECT FOR SHORT TO GROUND IN HIGHMOUNT BRAKE LIGHT Verify that the high-mount brake light, brake light (LH), brake light (RH) and rear body control module (RBCM) connectors are disconnected. Reconnect the high-mount brake light connector. Inspect for continuity between rear body control module (RBCM) terminal 4D (wiring harness-side) and body ground. Is there continuity?	Yes	Replace the high-mount brake light, then go to Step 13. (See HIGH-MOUNT BRAKE LIGHT REMOVAL/INSTALLATION .)
11		No	Go to the next step.
12	INSPECT FOR SHORT TO POWER SUPPLY IN HIGH-MOUNT BRAKE LIGHT Verify that the brake light (LH), brake light (RH) and rear body control module (RBCM) connectors are disconnected. Reconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5] .) Switch the ignition ON (engine off or on). Measure the voltage at the rear body control module (RBCM) terminal 4D (wiring harness-side). Is the voltage 0 V ?	Yes	Go to the next step.
12		No	Replace the high-mount brake light, then go to Step 13. (See HIGH-MOUNT BRAKE LIGHT REMOVAL/INSTALLATION .)
13	VERIFY THAT REPAIRS HAVE BEEN COMPLETED Always reconnect all disconnected connectors. Reconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION [SKYACTIV-G 2.0, SKYACTIV-G 2.5] .) Clear the DTC for the rear body control module (RBCM) using the M-MDS. (See CLEARING DTC [REAR BODY CONTROL MODULE (RBCM)] .) Depress the brake pedal. Retrieve the rear body control module (RBCM) DTCs using the M-MDS. (See DTC INSPECTION [REAR BODY CONTROL MODULE (RBCM)] .) Is the same DTC displayed?	Yes	Repeat the inspection from Step 1. If the malfunction recurs, replace the rear body control module (RBCM). (See REAR BODY CONTROL MODULE (RBCM) REMOVAL/INSTALLATION .) Go to the next step.
13		No	Go to the next step.
14	VERIFY IF OTHER DTCs DISPLAYED Are any other DTCs displayed?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [REAR BODY CONTROL MODULE (RBCM)] .)
14		No	DTC troubleshooting completed.