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Home / DTC / P21EA — Cylinder 8 Injector B Circuit Low

P21EA — Cylinder 8 Injector B Circuit Low

Detailed page for trouble code P21EA.

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Code

P21EA

Generic P — Powertrain

Cylinder 8 Injector B Circuit Low

Brand: Generic
Type: P — Powertrain
Views: UK: 9 EN: 15 RU: 10
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Page language: EN

Causes

  • Short to ground in the injector control wire for Cylinder 8 Injector B
  • Corroded, damaged or loose injector connector or terminals
  • Failed fuel injector (internal short or coil failure)
  • Open or high-resistance supply or ground (fuse, relay, chassis ground)
  • Faulty PCM/ECM injector driver transistor or internal fault
  • Incorrect installation or damaged harness after recent repairs

Symptoms

  • Malfunction Indicator Lamp (MIL) illuminated
  • Rough idle or misfire localized to cylinder 8
  • Reduced engine power, hesitation or surging under load
  • Increased fuel consumption or failed emissions test
  • Possible hard start when cold or after extended cranking

What to check

  • Retrieve all DTCs and freeze frame data; note freeze-frame RPM, load, and battery voltage
  • Visually inspect wiring and connector for cylinder 8 injector for damage, corrosion, melted insulation, or pin push-out
  • Check fuse(s) and relay(s) that feed the fuel injector rail and PCM power/grounds
  • Backprobe injector connector and verify supply voltage (B+) and driver signal while cranking/commanding the injector with a scan tool
  • Measure injector coil resistance with connector unplugged and compare to specification
  • Perform wiggle test on harness while monitoring signal to reproduce fault

Signal parameters

  • Injector supply voltage (B+): ~battery voltage (typically 11–14.5 V with engine off/crank/run)
  • Injector coil resistance (typical ranges): low-impedance injectors ~1–3 Ω; high-impedance injectors ~10–16 Ω — consult vehicle spec
  • Driver switching behavior: injector driver commonly switches to ground; expect pulsed signal from near B+ to ground when commanded
  • Pulse width: varies with load and RPM; typically a few milliseconds (e.g., 1–10 ms) depending on conditions
  • If driver is low-voltage faulting, measured control-pin voltage may be held near ground or significantly below B+ during commanded pulses

Diagnostic algorithm

  1. Record codes and freeze-frame data. Note operating conditions when fault set.
  2. Visually inspect the injector connector, wiring harness, and nearby components for damage, heat, or fluid intrusion.
  3. Check relevant fuses, relays, and battery voltage to ensure proper supply to injectors and PCM.
  4. With connector disconnected, measure injector coil resistance. If coil shows open or a short (outside spec), replace the injector.
  5. Reconnect and backprobe the injector connector. Use a scan tool to command the injector ON while monitoring supply and control signal. Verify supply is near battery voltage and control pin switches as expected.
  6. If control pin reads near ground or does not switch, inspect wiring continuity between the injector connector and PCM pin. Repair any short to ground or open circuits.
  7. Swap the suspect injector with a known-good injector from another cylinder if practical and supported (note safety/compatibility). If the fault follows the injector, replace the injector.
  8. If fault stays on Cylinder 8 after injector swap, check PCM driver output for that channel (with oscilloscope preferred) and verify grounds. If wiring is good and PCM output is faulty, consider PCM repair or replacement following manufacturer procedures.
  9. After repairs, clear codes and perform a test drive under conditions similar to the freeze-frame. Re-scan to confirm the code does not return.

Likely causes

  • Damaged insulation or pinched wiring in harness near cylinder 8
  • Corroded connector at injector making poor contact or partial short
  • Injector coil shorted to ground or internally failed
  • PCM driver output failed low or shorted to ground
  • Blown fuse or poor battery/ignition supply to the injector rail

Fault status

⚠️ Status
PCM detected low voltage on Cylinder 8 Injector B circuit during commanded injection. This indicates the injector drive signal or supply is below expected threshold (possible short to ground, bad connector, failed injector, or PCM driver fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1–3 hours

Similar codes

P0208 P0200 P0201
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