P21E1

Code

Generic P — Powertrain

Cylinder 3 Injector B Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 24 EN: 30 RU: 27

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Page language: EN

Causes

Short to battery/constant 12V on the injector control wire
Open or high-resistance connection in the injector harness or connector
Corroded or bent connector pins
Failed fuel injector (internal short or wiring fault)
Faulty ECU/PCM injector driver circuit
Poor or missing ground for the fuel injector circuit

Symptoms

Check Engine Light (MIL) illuminated
Rough idle or misfire on cylinder 3
Reduced power or hesitation under load
Hard starting or extended crank time
Increased fuel consumption and possible smoke
Intermittent drivability problems if fault is intermittent

What to check

Read/record all stored and pending codes and freeze frame data
Visually inspect injector connector, wiring harness and engine grounds for damage or corrosion
Backprobe injector connector with ignition ON and engine OFF to measure voltages
Measure injector coil resistance and compare to specification
Use a scope to view injector drive waveform while engine is running or cranking
Check for short to battery between injector control wire and 12V

Signal parameters

Reference (supply) side: typically ~12 V with key ON/engine OFF (varies by vehicle)
Control/driver side (low-side systems): normally near battery voltage when OFF, pulled to ~0 V (ground) when injector is commanded
Expected injector coil resistance: consult vehicle service manual (typical range ~1–16 Ω depending on low/high impedance injector)
Injector pulse width at idle: commonly 1–5 ms (varies with load and engine speed)
Pulse frequency increases with RPM; waveform should show clean square pulses when driven
Fault condition: control circuit reading stuck at battery voltage or higher than expected threshold

Diagnostic algorithm

Record codes and freeze frame data. Clear codes and attempt to reproduce under controlled conditions.
Visually inspect wiring, connector, and pins at cylinder 3 injector for damage, corrosion, or pin push-out. Repair as needed.
With ignition ON (engine OFF) measure voltage at the injector connector supply terminal and control terminal. Expect ~12 V on supply; control terminal should be ~12 V off and drop to ~0 V when commanded.
Measure injector coil resistance (engine cold) and compare to spec. Replace injector if out of range.
Backprobe the control terminal and start/crank the engine. Use a high-impedance voltmeter or oscilloscope to observe pulses. Look for proper pulsing to ground; a steady high voltage indicates a high/short condition.
Check for short to battery: disconnect connector and measure continuity between control wire and battery positive. Repair any short.
Swap the injector with a known-good injector from another cylinder. If code follows the injector, replace the injector.
If code does not follow injector, trace wiring back to ECU, check for opens/shorts and repairs. Repair damaged wiring or connectors.
If wiring and injector are good, test or replace the ECU/PCM injector driver only after confirming all other possibilities.
Clear codes and road test to confirm repair. Re-scan for related or secondary codes (misfire codes, fuel trim anomalies).

Likely causes

Shorted injector control wire to battery voltage at or near the cylinder 3 connector
Injector connector pin pushed out, corroded, or contaminated causing intermittent high voltage reading
Injector coil internal failure presenting abnormal resistance or leakage
Open low-side driver in the ECU so circuit remains at battery voltage
Shared circuit fault (fused/relay issue) feeding injector rail

Fault status

⚠️ Status

Cylinder 3 Injector B Circuit High — the control circuit for cylinder 3 injector B is reading higher than the expected voltage threshold. Possible electrical fault in wiring, connector, injector, or ECU driver. MIL illuminated.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours