P0291

Code

Generic P — Powertrain

Cylinder 11 Injector A Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 15 EN: 38 RU: 23

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Page language: EN

Causes

Short to ground in the injector A wiring for cylinder 11
Corroded, damaged or disconnected injector connector
Failed fuel injector (internal short or coil fault)
Faulty ECM/PCM low-side driver for injector A
Poor or missing power feed or ground to the injector circuit
Aftermarket modifications, wiring repairs, or pinched harness

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Rough idle or misfire localized to cylinder 11
Reduced engine power, hesitation or surging
Poor fuel economy and increased emissions
Possible hard starting or stalling under load

What to check

Read freeze-frame and live data with a scan tool; confirm P0291 and note conditions (battery voltage, engine rpm, load)
Visual inspection of cylinder 11 injector connector and wiring for damage, corrosion, pinched areas or aftermarket splice
Verify proper battery voltage at injector power feed with key ON (engine OFF)
Back-probe injector connector and check driver side voltage while commanding injector with a scan tool or while cranking
Measure injector coil resistance (compare to manufacturer spec or another cylinder)
Wiggle test wiring while monitoring for changes in signal or DTC

Signal parameters

Injector power feed (constant): approx. battery voltage (~11.5–14.5 V with engine running)
Injector driver output: low-side pulsed to ground when commanded; idle/state rest may read ~battery voltage on feed pin and ~open/float on driver pin
Expected injector coil resistance: typically ranges from ~1–16 ohms (low-impedance) to ~10–20 ohms (high-impedance); consult vehicle spec
When commanded, back-probe should show pulsed switching (voltage drop to ~0 V on driver) or a pulse waveform on scope
Current draw during injection varies by design; use injector current clamp or scope to confirm pulsed current when commanded

Diagnostic algorithm

Verify the code with a scan tool and record freeze-frame data. Clear code and attempt to re-create the fault to confirm repeatability.
Perform a careful visual inspection of the injector harness, connector, and nearby wiring for chafing, corrosion, heat damage, or aftermarket splices.
With key ON (engine OFF), measure battery voltage at the injector power pin. If absent, trace power feed/fuse/relay.
Back-probe the injector connector: with engine cranking or with injector commanded by a lab scope/scan tool, observe the driver pin. Expect pulsed switching to ground. If the driver pin reads continuously near 0 V (low) with key ON, suspect a short to ground or stuck driver.
Measure injector coil resistance (engine off, connector disconnected). Compare to spec or to another cylinder. Very low resistance suggests internal short; infinite/very high suggests open circuit.
Disconnect the injector harness at the connector. If the fault clears with the connector disconnected, the problem is in the harness or injector. If it remains, suspect ECM or shared circuit problem.
Perform a wiggle/motion test of harness while monitoring the circuit and for DTC reappearance to find intermittent faults.
If wiring and connector are good but the injector is faulty (out-of-spec resistance or fails swap test), replace the injector. If a swapped known-good injector causes the code to follow the harness, repair the wiring.
If wiring and injector test good, test the ECM driver output per manufacturer procedure. If ECM driver is shorted or failed, replace or reprogram ECM as directed by OEM service instructions.
After repairs, clear codes and perform a test drive to confirm the fault does not return and that the engine runs normally.

Likely causes

Wiring short to ground at or near the cylinder 11 injector connector
Faulty/corroded connector or pin (poor contact)
Defective injector coil (internal short or low resistance)
ECM driver transistor failure (less common)
Bad power feed or engine ground affecting circuit voltage

Fault status

⚠️ Status

P0291 — Cylinder 11 Injector A Circuit Low. The ECM has detected a low-voltage condition on the low-side injector circuit for cylinder 11, indicating a wiring short, connector issue, defective injector, or ECM driver fault.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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