Powertrain, generic (extended)

P21EC Cylinder 9 Injector B Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P21EC signals a low circuit state, usually a grounded wire or, depending on the maker, also a break, on the B injector of cylinder 9. It can only occur on an engine with at least nine cylinders and two injectors per cylinder. No manufacturer documents it publicly; GM's and Ford's lists stop at cylinder 8. The one such engine on record is Lamborghini's Huracán V10, which combines direct and multi-point injection; which of the two it calls B is not published. Its firing order alternates between cylinders 1 to 5 and 6 to 10, so cylinder 9 belongs to the second bank. CARB requires circuit monitoring of such output components. By analogy with GM's V8, a ground below about 0.5 Ohm on the switched-off low side would count. Open circuit: P21D7; high fault: P21ED.

Likely causes

Cylinder 9 B injector wire shorted to ground
Broken wire, if the maker reports opens under the low code
Injector coil shorted to housing or open
Engine control module output faulty

Symptoms

  • Check engine light on
  • Misfire or rough running on cylinder 9
  • Mixture deviation on the bank of cylinder 9

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–1,200
Time1–5 h

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

Parts involved

fuel injectorinjector wiringengine control module

Related codes

P21EDP21D7P0285P21EAP21EEP0309

References: law.cornell.edu, en.wikipedia.org, gsi.ext.gm.com.