Hydraulic Brake Conditions on Electric/Hybrid Vehicles

There may be several brake system conditions on the 2016-2017 Volt and Malibu Hybrid (RPO HP4) that could be related to the hydraulic components. These types of hydraulic issues should not be overlooked when diagnosing a condition on electric/hybrid brake systems.


Misrouted brake line – A misrouted metal brake line may cause the line to kink (Fig. 11), which would reduce the brake apply pressure to the wheel. 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.



Fig. 11


Worn rubber brake hose – If the anti-rotation bracket is not seated into the hole properly, the rubber brake hose could rub through on the front wheel. (Fig. 12) This condition could lead to a loss of brake fluid and brake apply. DTCs C05AD, C0580 (Brake Booster Motor “A” Phase U-V-W Circuit Low), P05FF (Brake Pressure Sensor and Brake Pedal Position Sensor Correlation) may set.



Fig. 12


Twisted rubber brake hose – A Master Cylinder (MC) line from the Secondary Port to MC2 that is twisted 360 degrees (Fig. 13) may cause pressure to get trapped in the brake system. This condition may cause a concern during a light coast with a light brake apply at 45 mph (72 km/h). DTC C05AD may set along with illuminated ABS, traction control and Check Engine warning lamps.



Fig. 13


Bent brake caliper slide pins – If the right front bleeder screw is bent/cracked or the brake rotor shows uneven pad contact, check for a bent caliper guide pin. (Fig. 14) A bent pin may cause the brake warning light to illuminate or set DTC C05AD.



Fig. 14


Leak at caliper brake hose – A brass crush washer can only be used one time. (Fig. 15) Reusing a brass crush washer may cause a leak. Look for the crush washer to have an oval shape and witness lines indicating multiple use. Always discard washer and replace with a new brass crush washers.



Fig. 15


A leak also may be due to the crush washer bolt being cross-threaded (Fig. 16) and retightened. When tightening the crush washer bolt, make sure to finger tighten the bolt to guide to avoid cross-threading when reinstalling.



Fig. 16


– Thanks to Keith Newbury

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