Pinpoint Test J: DTC C1991
Anti-Lock Control
Pinpoint Tests
Pinpoint Test J: DTC C1991
Normal Operation
The ABS module needs to be calibrated whenever a component specific to the Electronic Stability Control (ESC) system is disconnected or a new component is installed. Calibration allows the ABS module to identify the "zero position" of the sensors so the system will operate correctly.
- DTC C1991 (Module Calibration Failure) - If the IVD Initialization sequence does not finish or if the ABS module loses the calibration information, DTC C1991 will set.
This pinpoint test is intended to diagnose the following:
- ABS module
- Restraints Control Module (RCM)
- Steering wheel rotation sensor
PINPOINT TEST J: DTC C1991
NOTE: The stability/traction control indicator (also known as the sliding-car icon) will flash when a system calibration is required. Calibration is required after certain DTCs are cleared.
NOTE: The vehicle must be on level ground, at a complete standstill, in NEUTRAL with the brakes applied, and not on a hoist while carrying out the calibration procedure. Any vehicle movement will result in calibration failure.
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J1 CHECK FOR ABS MODULE DTCs
- Connect the scan tool.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Self Test - ABS Module.
- Retrieve and record any ABS module DTCs.
- Is any other DTC retrieved with C1991?
Yes
DIAGNOSE all other DTCs first. GO to the ABS Module DTC Chart. Diagnostic Trouble Code Tests and Associated Procedures
No
GO to J2.
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J2 CALIBRATE THE ABS MODULE
- Using the scan tool, carry out the IVD Initialization sequence. Follow the scan tool instructions.
- Does the IVD Initialization sequence complete for all of the stability sensors and does the sliding-car icon stop flashing and turn off?
Yes
GO to J3.
No
GO to J4.
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J3 CHECK FOR RETURNING DTCs
- Using the scan tool, clear the ABS module DTCs.
- Ignition OFF.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Self Test - ABS Module.
- Retrieve and record any ABS module DTCs.
- Does the DTC C1991 clear and not return?
Yes
The calibration is complete. The concern may have been caused by an incorrect or incomplete calibration.
No
GO to J4.
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J4 CHECK FOR CORRECT ABS MODULE OPERATION
- Disconnect: ABS Module C135.
- Check ABS C135 for:
- corrosion.
- spread terminals.
- pushed-out pins.
- Connect: ABS Module C135.
- Make sure the connector seats properly, then operate the system and verify the concern is still present.
- Is the concern still present?
Yes
INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module Service and Repair. CLEAR the DTCs. REPEAT the self-test.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. CARRY OUT the self-test with the brake pedal not applied.
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