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A couple days ago, I did a typical tune up on my old lady's car (plugs, filters, oil). After finishing, I noticed her brake pedal is extremely hard to depress, and it doesn't stop the car very well. I disconnected the negative battery lead before starting, and got to work. Never touched any of the brake lines or anything, so I'm very confused as to how this happened. I typically work on older vehicles, primarily GMs, so I'm not very knowledgeable on how these newer cars work. Initially, I thought there might be built up pressure in the line, so I went ahead and bled the lines. Still nothing. As of now, there's a green bar on the dash that fills up with small white bars as I'm driving (no clue what that is) and a symbol for the brake pedal above it. Haven't had time to get a picture, but if it would help, I can try to get one up when I'm off of work. Any help would be much appreciated.
 

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NF Mod/Nissan Master Tech
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A hard brake pedal, one that feels like it has no power assist, usually occurs when there is an issue with the brake booster, for example, the vacuum hose was disconnected or the one-way valve has failed or installed backwards. So, that's what I would look at first. Any more than that and we would need more information about the vehicle, as in year/model/drivetrain.
 

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A hard brake pedal, one that feels like it has no power assist, usually occurs when there is an issue with the brake booster, for example, the vacuum hose was disconnected or the one-way valve has failed or installed backwards. So, that's what I would look at first. Any more than that and we would need more information about the vehicle, as in year/model/drivetrain.
exactly what he said. however i have encountered before on a few cars the master itself binds up and the plunger spins the piston ever so slightly which can cause the same issue you are describing.

more thoughts to add to this, what color is the brake fluid? abs equipped or non abs. if abs you may have a abs metering valve fault as they are electronic and may have disconnected a wire by accident while doing the routine maintenance. start by bleeding the brakes, sometimes some crud can work its way into the brake system (pieces of hose or orings from other components) and can clog the abs valve and cause this issue. if bleeding doesnt solve the problem or improve it check the abs valve then the vacuum to the brake booster as smj suggested and go down the list methodically till the issue is found
 
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