Powertrain, generic (extended)

P21D2 Cylinder 4 Injector B Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P21D2 reports an open in the drive circuit of the B injector on cylinder 4. On four-cylinder engines with dual injection it is the last of the set, for example Ford's 2.0 EcoBoost from 2022 or the 2.3 introduced for the 2024 Mustang, both of which added port injectors to direct injection. Ford tests it like its siblings, continuously with at least 11 V and a 5 s window, and assigns letter A to the direct injector (P0204). Mitsubishi, whose Eclipse Cross uses B for the direct injectors, has no open code here and files such faults under the low code P21E2. On Ford's 3.5 V6 cylinder 4 opens the second bank. In GM's 2019 LT5 module the check samples every 100 ms. Expect a misfire on cylinder 4.

Likely causes

Open winding in the cylinder 4 port injector
Wire broken at a bend or clip near the intake manifold
Corroded or loose injector connector

Symptoms

  • Check engine light on
  • Misfire on cylinder 4 (P0304)
  • Uneven idle

Repair estimate

DifficultyMediumDIY possible
Parts and labour€80–500
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injectorinjector wiringengine control module

Related codes

P0204P21E2P21E3P21D1P21D3P0304

References: fordservicecontent.com, en.wikipedia.org, mitsubishitechinfo.com.