Powertrain, generic (extended)

P21E4 Cylinder 5 Injector B Circuit Low

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

P21E4 flags a low state on the circuit of the second (B) injector serving cylinder 5. The only public OBD summary that lists it is GM's for the 2019 Corvette ZR1, whose supercharged LT5 V8 pairs direct injectors with port injectors and drives the supplemental ones from a separate fuel injection control module (FICM). While that driver is off, a low side reading 0.5 Ohm or less toward ground in 20 of 25 samples, taken every 100 ms, is judged a short and becomes a Type A fault with the MIL in the first trip. On GM's V8 numbering cylinder 5 is the third cylinder of the left bank, i.e. bank 1. Because a grounded low side can let the injector flow uncommanded, a rich bank 1 may follow. Ford's dual-injection engines report B shorts on this cylinder only as P21D3.

Likely causes

Low-side wire of the cylinder 5 B injector touching ground

Injector winding shorted to its housing

Moisture or corrosion in the injector connector

Driver stage in the injection control module faulty

Symptoms

Check engine light on
Rich running or fuel trim pulled back on bank 1
Rough idle or misfire on cylinder 5

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–900

Time1–4 h

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

Parts involved

fuel injectorinjector wiringengine control module

References: gsi.ext.gm.com, lsxmag.com, fordservicecontent.com.