Sometimes an engineer might not be performing up to expectations because their manager is unable to provide them clear expectations for their level. If they feel like that's the case in the face of a PIP, what courses of action do they have to push against the PIP?
Unfortunately, in most cases, the answer is not much. That's probably not the answer you want to hear, and it does suck because many PIPs are certainly undeserved.
If you're on a PIP, your best bet in 99% of cases is to accept it and start prepping for a new job. Once the PIP is filed, your manager has spent hours of work explaining your shortcomings, likely with evidence or feedback from peers. If there was an opportunity to push back against a PIP, it probably needs to happen a few weeks before the PIP is officially declared.
Even if you feel you have a claim about your manager being biased or just a jerk, your options are:
Neither is a winning strategy since your skip manager will almost certainly not override their report, and the primary role of HR is to protect the company, not you.
This one is particularly hard as they can seem to even try to hold out hope that having you in the chair is better than having no one there at all. I was very proactive 2 months into my new role telling them it wasn't working out for me and there was a general dismissal of the situation. 2 months and a low performance discussion later, I'm resigning to start my own startup where my skills align with the job description. What I'm trying to say is realistically, even the best folks get put in unavoidable situations unfortunately.