Nissan Versa P2138 Fault: Pedal Power Loss and Engine Light On

I recently purchased a Nissan Versa from a pre-owner and am now experiencing intermittent pedal power loss, along with the service engine light illuminating. After taking it to a Nissan dealership for diagnosis, they identified OBD fault codes P2138 and P0731. The technician initially suggested replacing the brake pedal, but after the replacement, the issue returned. A follow-up inspection revealed that the engine compartment harness needs replacement, which costs approximately $3,000—nearly equal to my original purchase price. Given this high cost, I'm seeking advice: is this repair truly necessary? Are there alternative diagnostics or cheaper solutions available for a Nissan Versa with P2138 code?