| Subject: | Low Brake Fluid Level Source Of Leak Unknown |
| Models: | 2007-2008 Cadillac Escalade, Escalade ESV, Escalade EXT |
| 2007-2008 Chevrolet Avalanche, Silverado, Suburban, Tahoe |
| 2005-2007 Chevrolet Silverado Classic with RPO JF3 or JF7 |
| 2005-2007 GMC Sierra Classic with RPO JF3 or JF7 |
| 2007-2008 GMC Sierra, Yukon, Yukon Denali, Yukon XL, Yukon Denali XL |
This PI was superseded to update models. Please discard PIT3559.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Owners may comment of a low brake fluid level or red brake warning indicator/service brake system message. During normal diagnostics, the source of the leak cannot be found. The leak could be from the rear of the master cylinder. The back of the master
cylinder is no longer sealed from engine vacuum at the brake booster. If a leak should occur at the back of the master cylinder, the fluid would be ingested into the booster and/or engine.
Recommendation/Instructions:
If the source of the leak is determined to be from the master cylinder, BOTH the master cylinder and brake booster should be replaced.
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.
