(Hybrid) No Brake Assist After a Battery Disconnect - keywords 2 2-mode battery hp2 inoperative mode performance power two two-mode

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

No brake assist ( Hard Pedal ) after disconnecting the battery. This may also be followed by an ABS and red brake lamp with a possible DTC C121D 00 and C056D 00 being set in the EBCM. This may be caused by an improper 12v battery disconnect procedure.

Technicians that are disconnecting the battery must wait for a period of at least 1 minute with the ignition in the "OFF" position prior to disconnecting the negative battery cable. During this one minute wait period it is critical that the key does not pause in the ACCESSORY mode, During this period it is also critical that the brake pedal is NOT depressed. Due to programmed parameters, it is necessary to allow the brake system pressure relief procedure to occur without interruption. Failure to follow these steps may result in warning lamps and/or DTCs being set pertaining to interruption of the pressure relief procedure. Other vehicle systems may also be affected by not allowing a 1 minute duration for power-down.

If the 12V battery is disconnected prior to the completion of the brake system pressure relief procedure the next key "On" drive cycle may present a hard brake pedal with little or no brake assist.

If the vehicles battery is disconnected prior to waiting the 1 minute period, please follow these steps to resolve the concern:

1. Install the negative battery cable to the battery.
2. Rotate the lever lock clockwise until an audible click is heard in order to connect the negative battery cable to the battery.
3. Position the negative battery cable insulating cover over the negative terminal.
4. Start the vehicle without stepping on the brakes
5. Shut the vehicle " Off " for one minute
6. Restart vehicle and check brakes for proper operation.
7. Clear codes in the ECM and the EBCM.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.