Hydraulic Brake Conditions on Hybrid Vehicles Update

Several brake system conditions that may be found on some 2016-2019 Volt and Malibu Hybrid (RPO HP4) models could be related to the hydraulic components. Be sure to not overlook kinks in the brake lines, brake fluid leaks, damaged brake calipers and other types of hydraulic brake system issues when diagnosing a brake condition on hybrid models.

Following are some examples of possible conditions that may occur on the hydraulic brake systems of hybrid vehicles.

Misrouted Brake Line – A misrouted metal brake line may cause the line to kink, which would reduce the brake apply pressure to the wheel. (Fig. 16) DTC C05AD (Brake Blending System Performance) may set. This condition could occur if the misrouted line hits the shock tower when the wheel is turned. Repair the kinked metal brake line.

 

Fig. 16

 

Worn Rubber Brake Hose – If the anti-rotation bracket is not seated into the retaining hole properly or the hose is not properly secured, the rubber brake hose could rub through on the front tire. (Fig. 17) DTCs C05AD, C0580 (Brake Pedal Position Sensor Performance) and/or P05FF (Brake Pressure Sensor and Brake Pedal Position Sensor Correlation) may set. This condition could lead to a loss of brake fluid. Replace and properly secure the brake hose.

 

Fig. 17

 

Twisted Rubber Brake Hose – A flexible brake hose that is kinked or twisted at the master cylinder may cause pressure to get trapped in the brake system. (Fig. 18) DTC C05AD may set. This condition may cause reduced brake fluid apply pressure to the wheels, resulting in brake performance issues. Replace the flexible brake hose at the master cylinder.

 

Fig. 18

 

Bent Brake Fluid Bleeder Valve – Each brake caliper has a brake fluid valve. If any of the front or rear brake fluid bleeder valves are bent or cracked (Fig. 19), which may be caused by a road debris impact, replace the damaged bleeder valve.

 

Fig. 19

 

Damaged Brake Caliper Guide Pins – The brake caliper guide pins are designed to align the brake pads to meet the rotor at the correct angle in order to ensure complete application. If the brake caliper guide pins are suspected of causing a brake performance issue, remove the pins and check for any corrosion, damage, distortion, lack of high temperature lubrication, looseness in the caliper mounting bracket, a missing or damaged lower guide pin bushing, a missing or improperly seated guide pin seal, restricted pin movement, damaged guide pin boots, or seized or binding caliper guide pins. (Fig. 20) DTC C05AD may set. If any of these conditions are found, replace the guide pins.

TIP: The Malibu Hybrid and Volt brake caliper guide pins have several design differences and different removal and installation procedures. Refer to the appropriate Service Information when servicing the brake caliper guide pins.

 

Fig. 20

 

Leak at Caliper Brake Hose to Caliper – A brake hose caliper crush washer can only be used one time. (Fig. 21) Reusing a brass crush washer may cause a leak. Look for the crush washer to have an oval shape and witness lines, which indicate multiple use. Always discard the washer and replace with a new brass crush washer.

TIP: On Malibu Hybrid applications, the brake hose caliper crush washers are also identified as brake hose fitting gaskets. On Volt applications, the sealing washers are also identified as brake hose fitting gaskets.

 

Fig. 21

 

A leak also may be due to the crush washer bolt being cross-threaded and retightened. (Fig. 22) When tightening the crush washer bolt, make sure to finger tighten the bolt first to avoid cross-threading when reinstalling.

If either of these conditions are encountered, replace the brake hose.

 

Fig. 22

 

For additional information, refer to the latest version of Bulletin #16-NA-286.

 

– Thanks to Sherman Dixon

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