P21D5: Cylinder 7 Injector B Circuit/Open

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.

Medium severity. Can I keep driving?Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

Cylinder 7 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

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

Most likely causes

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

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring of the injector indicated
Check the continuity of the wire between the component and the control module.
Measure the resistance and compare it with the manufacturer's specification
Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
On diesels, check the per-cylinder injection corrections

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P21D5 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
1: Air and fuel
D5: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21D5?

Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

What causes code P21D5?

The most common causes are: open winding in the cylinder 7 port injector; broken wire or terminal in the port injector harness of that bank; separate fuel injection control module faulty (GM LT5).

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.