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Free to use workshop manual for your 2015+ Mk4 'ND' Mazda MX-5

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DTC C1A90:12/C1A90:16 [DSC HU/CM]

DTC	C1A90:12	ABS wheel-speed sensor power supply
	C1A90:16
DETECTION CONDITION		Malfunction detected in ABS wheel-speed sensor power supply voltage.
FAIL-SAFE FUNCTION		Refer to “Fail-safe function table”. (See DTC TABLE [DSC HU/CM].)
POSSIBLE CAUSE		Short to ground circuit in wiring harness between ABS wheel-speed sensor (LF) terminal B and DSC HU/CM terminal S Short to ground circuit in wiring harness between ABS wheel-speed sensor (RF) terminal B and DSC HU/CM terminal J Short to ground circuit in wiring harness between ABS wheel-speed sensor (LR) terminal A and DSC HU/CM terminal R Short to ground circuit in wiring harness between ABS wheel-speed sensor (RR) terminal A and DSC HU/CM terminal M Poor connection at each connector DSC HU/CM malfunction

Diagnostic Procedure

Step	Inspection		Action
1	INSPECT ABS WHEEL-SPEED SENSOR POWER CIRCUIT FOR SHORT TO GROUND CIRCUIT Disconnect the ABS wheel-speed sensor connector. Inspect for continuity as followings: ABS wheel-speed sensor (LF) terminal B (wiring harness-side)—body ground ABS wheel-speed sensor (RF) terminal B (wiring harness-side)—body ground ABS wheel-speed sensor (LR) terminal A (wiring harness-side)—body ground ABS wheel-speed sensor (RR) terminal A (wiring harness-side)—body ground Is there continuity?	Yes	Refer to the wiring diagram and verify whether or not there is a common connector in the followings: ABS wheel-speed sensor (LF) terminal B—DSC HU/CM terminal S ABS wheel-speed sensor (RF) terminal B—DSC HU/CM terminal J ABS wheel-speed sensor (LR) terminal A—DSC HU/CM terminal R ABS wheel-speed sensor (RR) terminal A—DSC HU/CM terminal M 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 circuit. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has a short to ground circuit. Go to Step3.
		No	Go to the next step.
2	INSPECT ABS WHEEL-SPEED SENSOR POWER CIRCUIT FOR OPEN CIRCUIT Disconnect the ABS wheel-speed sensor connector. Disconnect the DSC HU/CM connector. Inspect for continuity as followings: ABS wheel-speed sensor (LF) terminal B (wiring harness-side)—DSC HU/CM terminal S (wiring harness-side) ABS wheel-speed sensor (RF) terminal B (wiring harness-side)—DSC HU/CM terminal J (wiring harness-side) ABS wheel-speed sensor (LR) terminal A (wiring harness-side)—DSC HU/CM terminal R (wiring harness-side) ABS wheel-speed sensor (RR) terminal A (wiring harness-side)—DSC HU/CM terminal M (wiring harness-side) Is there continuity?	Yes	Go to the next step.
		No	Refer to the wiring diagram and verify whether or not there is a common connector in the followings: ABS wheel-speed sensor (LF) terminal B—DSC HU/CM terminal S ABS wheel-speed sensor (RF) terminal B—DSC HU/CM terminal J ABS wheel-speed sensor (LR) terminal A—DSC HU/CM terminal R ABS wheel-speed sensor (RR) terminal A—DSC HU/CM terminal M 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 the next step.
3	VERIFY DTC TROUBLESHOOTING COMPLETED Using the M-MDS, clear the DTC from the DSC HU/CM. (See CLEARING DTC [DSC HU/CM].) Using the M-MDS, perform the DSC HU/CM DTC inspection. (See DTC INSPECTION [DSC HU/CM].) Is the same DTC present?	Yes	Repeat the inspection from Step1. If the malfunction recurs, replace the DSC HU/CM, then go to the next step. (See DSC HU/CM REMOVAL/INSTALLATION.)
		No	Go to the next step.
4	VERIFY NO DTC IS PRESENT Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [DSC HU/CM].)
		No	DTC troubleshooting completed.

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