What is P1351 code?

Trouble code P1351 means: Ignition Diagnostic Monitor Input Circuit

ALWAYS remember, a proper diagnosis is not based on code retreival only !! For this particular code, you must also check for the presence of other codes (very important), and, spark quality, fuel pressure-including leak down test, inj pulse, compression test, timing chain slack test. Compression @140 is good, no cylinder below 110. fuel pressure @60KOEO @50-55 KOER less than 15 degrees lack in chain.

Since this code can also be generated by extended cranking time, and no other codes present- It lends itself to a variety of other conditions that are within operating ranges according to O2 sensors but are gradually failing.

Try clearing code and seeing if will reset right away, and how hard is vehicle to start when hot, or when cold. What is the ECT & IAT when engine is cold.

Or other non-coded conditions when is observed to be running RICH, such as, just needs a full tuneup. Or problem with GM CFI bad injection unit, or fuel pressure regulator leaking. When running compression test (plugs out-duh) disable ignition spark. Now as an assistant cranks engine, observe gas vapor or stream coming from any cylinders. This could pin point cause of "rich condition" possible bad injection uint-of course based on pertint pin point test from here.

GM injection unit is often difficult to diagnose, even by an experienced tech (96-99vortech-cfi). Given that these vehicles are also prone to failed fuel pumps (no code given). Intake manifold problems, and MAF sensors subject to contamination (again no code). You really need to take your time and not be rushed to get the diagnosis right the 1st time without wasting money on parts you don't need.

A good technician will charge a flate rate initial diagnostic fee-including the basic checks listed above. As you can see their would often be Secondary checks required upon code or condition. The charge here will be an hourly rate that would not normally exceed 2-3hours MAX. These charges typically range from 1-2 hours, three would be Max unless your vehicle is warn, and has multiple problems. Or is a 'classic/rare/collector car'.