P21D4: Cylinder 6 Injector B Circuit/Open

What does P21D4 mean?

P21D4 is the last B injector code on a six-cylinder engine. Ford's second-generation 2.7 and 3.5 EcoBoost V6 combine port and direct injection, label the port injectors B and test this circuit together with P21CF to P21D3, continuously above 11 V within 5 s; on these engines cylinder 6 is the rear cylinder of the second bank. On the 3.5 the direct system is shut down at low speed and light load and the engine runs on port fuel alone, so an open cylinder 6 port injector is most noticeable at idle and in gentle driving. GM's 2019 LT5 V8 also covers cylinder 6 in its injection module, Type A after 20 of 25 failed samples. The A-side direct injector code is P0206, the misfire code P0306; P21E6 and P21E7 are the low and high faults.

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

Symptoms

• Check engine light on
• Misfire on cylinder 6 (P0306)
• Slightly rough idle

Common causes

• High Port injector of cylinder 6 open internally
• Medium Damaged wire at the rear of the engine, hard to inspect
• Medium Connector not fully latched after earlier work on the intake

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