P21D5: Cylinder 7 Injector B Circuit/Open

What does P21D5 mean?

P21D5 belongs to V8 engines with a second injector per cylinder. Two are documented: Ford's 5.0 V8, which gained direct injection alongside its port injectors in 2018, and GM's 2019 LT5, the supercharged Corvette ZR1 engine with primary direct and supplemental port injection. Ford's summary lists P21CF to P21D6 as port injector circuits, continuous above 11 V, 5 s. On the LT5 the B injectors hang on a separate injection module whose low-side driver flags an open at 200 kOhm or more with the output off, in 20 of 25 samples at 100 ms, Type A with MIL in one trip. Ford counts its V8 one bank after the other, so cylinder 7 lies on the second bank; GM alternates banks, making 7 the last cylinder on the left. The A-side code for cylinder 7 is P0207, the misfire code P0307.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on
• Misfire on cylinder 7, on the LT5 mostly under high load
• Reduced power at full throttle

Common causes

• High Open winding in the cylinder 7 port injector
• Medium Broken wire or terminal in the port injector harness of that bank
• Low Separate fuel injection control module faulty (GM LT5)

Likelihood is a general estimate across vehicles; your make and model may differ.