P21D6

Code

Generic P — Powertrain

Cylinder 8 Injector B Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 25 EN: 45 RU: 22

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Page language: EN

Causes

Wiring open between ECM and cylinder 8 injector B (broken wire, chafing, or disconnected connector)
Corroded/poor connector or pin at injector or harness
Faulty injector (open internal coil)
Faulty ECM injector driver (open/failed output)
Blown or missing fuse or relay supplying injector circuit (where applicable)
Poor ground or high-resistance ground in related circuit

Symptoms

Check Engine Light (MIL) illuminated
Diagnostic trouble code P21D6 stored
Engine misfire on cylinder 8 or rough idle
Loss of power under load
Poor fuel economy
Possible fuel smell or increased emissions

What to check

Scan for stored codes and freeze-frame data; record related codes (misfire/fuel trim)
Visually inspect wiring and connector at cylinder 8 injector for damage, corrosion, or looseness
With key ON (engine OFF) check for battery voltage at injector supply circuit (if applicable)
Measure injector coil resistance with multimeter (expect continuity; infinite = open)
Back-probe injector control pin while cranking/starting to verify injector drive pulses (use noid light or oscilloscope)
Check for continuity between ECM connector pin and injector connector pin; check for short to power or ground

Signal parameters

Injector supply voltage (key ON, engine OFF): ~battery voltage (nominal ~12V) at the supply terminal (if system uses dedicated supply)
Injector coil resistance: typically a few ohms for low-impedance injectors or ~10–16 ohms for high-impedance designs — an open reads infinite/OL
Driver output: PWM pulse to ground during operation; amplitude typically rising to near battery voltage when inactive and pulled to ground when driven
Noid light/oscilloscope: pulsed waveform while cranking or running; no pulse indicates open circuit or driver fault

Diagnostic algorithm

Read and record all stored/related codes and freeze-frame data. Clear codes and perform an ignition cycle to confirm code returns.
Visually inspect injector #8 harness and connector for damage, corrosion, bent pins, or evidence of repairs. Repair visible damage before further testing.
With ignition OFF, disconnect injector connector and measure injector coil resistance. If infinite/OL, suspect open injector — replace or bench-test.
With key ON (engine OFF), check for battery/feed voltage at the injector supply terminal (if applicable). No feed indicates wiring/fuse/relay issue.
Reconnect and back-probe the injector control terminal. Crank or run engine and check for driver pulses using a noid light or oscilloscope. No pulse with proper supply suggests open in control circuit or failed ECM driver.
If no pulse, perform continuity check between ECM driver pin and injector connector pin (with connectors disconnected). An open indicates wiring/harness fault; repair wiring or connector.
If wiring is good and supply present but still no injector function, swap injector B of cylinder 8 with another cylinder’s injector B (where possible and safe) and see if code or misfire follows the injector. If it follows the injector, replace injector.
If problem follows the ECM pin (code stays on cylinder 8 even after swapping injectors), consider ECM driver fault — consult manufacturer procedures before ECM replacement.
After repair or component replacement, clear codes and verify repair by road test and confirming no return of fault and proper engine operation.

Likely causes

Damaged harness/connector at cylinder 8 (most common)
Corroded or pushed-out terminal at injector connector
Injector coil open (internal failure)
ECM output driver failure (less common)

Fault status

⚠️ Status

ECM detected open/infinite resistance in Cylinder 8 Injector B circuit (no continuity or no driver pulse). Inspect wiring, connector, injector coil, supply/ground and ECM driver.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours