P21E9

Code

Generic P — Powertrain

Cylinder 7 Injector B Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 18 EN: 30 RU: 18

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Page language: EN

Causes

Short to battery / B+ on the injector B circuit for cylinder 7
Corroded or damaged injector connector or wiring harness
Internal short or failure in the fuel injector
Faulty ECM/PCM injector driver transistor or internal electronics
Poor or missing ground(s) affecting the injector driver circuitry
Intermittent connector contact (water, oil, debris)

Symptoms

Malfunction Indicator Lamp (MIL) on
Rough idle or engine misfire on cylinder 7
Reduced engine power and acceleration
Poor fuel economy and increased emissions
Possible hard starting or intermittent stalling
P0307 or misfire-related codes may be present

What to check

Read freeze frame and live data with a scan tool; note injector pulse width and command status
Visually inspect wiring and connector for cylinder 7 injector B (corrosion, pin damage, chafing, heat damage)
Backprobe injector connector and measure voltage with key ON and engine cranking/ running
Check injector coil resistance with a multimeter and compare to factory spec
Perform wiggle test on wiring/connectors while monitoring live data for changes
Use an oscilloscope to view the injector command waveform for abnormal steady high voltage

Signal parameters

Injector command waveform: pulsed switching (0–12 V depending on system); verify transitions when injector is commanded
Pulse width: varies with load — typically a few milliseconds at idle, longer under load (check service spec)
Injector coil resistance: refer to vehicle specification (common ranges: ~2–18 Ω depending on high/low impedance design)
Supply voltage to injector connector (Key ON): ≈ battery voltage on the supply pin; driver pin should switch according to design
Injector current when energized: varies by design (use oscilloscope/current probe if available)

Diagnostic algorithm

Retrieve DTC(s) and freeze frame with a scan tool; note related misfire or fuel trim codes.
Visually inspect the cylinder 7 injector, connector, and wiring for damage, corrosion, melted insulation, or evidence of shorts.
With key OFF, disconnect the injector connector and measure coil resistance at the injector pins; compare to spec. If out of range, consider replacing the injector.
With key ON (engine off), backprobe the connector to check for constant supply voltage on the injector supply pin and proper reference/driver state on the control pin.
Start the engine or crank while monitoring the control pin: verify the driver is pulsing and that voltage swings are within expected ranges. Use an oscilloscope if available to confirm a clean pulsed waveform. A continuously high voltage on the driver pin indicates a 'high' condition.
Perform a wiggle/test while monitoring live data to isolate intermittent faults. Check continuity to ground and continuity to battery where appropriate.
Swap the suspected injector with another known-good injector (e.g., cylinder 6) and re-scan. If the code moves with the injector, the injector is faulty. If the code stays on cylinder 7, the wiring or PCM is likely at fault.
If wiring and injector check good, check ECM/PCM grounds and supply voltages. Test the PCM driver output for short to battery or replace the PCM as a last step per manufacturer procedures.
After repairs, clear codes and perform a road test to confirm the issue is resolved.

Likely causes

Wiring short to battery (most common for a 'circuit high' code)
Corroded/damaged connector at injector
Failed injector with internal electrical fault
ECM/PCM driver failure (diagnose after wiring and injector verified good)

Fault status

⚠️ Status

ECM detected high voltage on Cylinder 7 Injector B circuit (Injector driver/ circuit voltage above expected threshold). Possible short to battery, connector/wiring fault, failed injector, or ECM driver issue.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours