I have a 98 E-150 5.7L with around 130k on it and there's been a problem with the brakes I'd like to fix before they cause an accident. While driving at any speed, I occasionally need to apply the brakes several times before they engage. When the ABS engages, it clamps hard one time and then releases. When that happens I have to take my foot off the pedal and reapply in order for it to come to a complete stop. What is going on and what do I need to replace? I've also scanned it for codes and po171 - po174 show up but those have nothing to do with the brakes. Also, what's the most common issue that brings up those codes? Any help would definitely be appreciated.

 

unless you have a full function scan tool that read chassis codes you will not be able to check for abs related dtc. any abs lights illuminated?

without looking, I think p0171 and 172 are fuel trim lean dtc. Do you have a big vacuum leaks? that could both the fuel trim and brake booster.

 

There's only a check engine light that's on and I just have a cheap scan tool unfortunately. There isn't any obvious vacuum leaks. You're right about it being a lean condition too. It still runs as good as it always has, that light came on back in April. I don't drive it very often..