P21E4: Cylinder 5 Injector B Circuit Low

What does P21E4 mean?

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.

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

Symptoms

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

Common causes

• High Low-side wire of the cylinder 5 B injector touching ground
• Medium Injector winding shorted to its housing
• Medium Moisture or corrosion in the injector connector
• Low Driver stage in the injection control module faulty

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