P0291
Cylinder 11 Injector Circuit Low
If your vehicle's onboard computer has flagged the diagnostic trouble code P0291, it refers to a detected anomaly regarding "Cylinder 11 Injector Circuit Low". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
Your vehicle's computer logged P0291 after detecting a malfunction in the cylinder 11 injector circuit low system. In practice, this fault causes engine shaking, lack of power on acceleration. Given the high severity of this code, continuing to drive risks significant mechanical damage. Have it diagnosed immediately.
Symptoms
Engine shaking, lack of power on acceleration
Common Causes
- Defective Cyl 11 fuel injector
- Wiring harness shorted to ground
- Corroded injector plug
- PCM driver failure
How to Fix
- 1 Replace Cyl 11 fuel injector
- 2 Repair wiring harness
- 3 Clean electrical contacts
- 4 Reflash or replace PCM
Technical Explanation
The ECM detects code P0291 by continuously monitoring the relevant sensor circuit against calibrated threshold values stored in its non-volatile memory. The PCM monitors crankshaft rotational velocity via the CKP sensor at a resolution of individual tooth gaps on the reluctor ring. A combustion event in each cylinder produces a measurable acceleration spike; its absence or weakness is flagged as a misfire event within a 200-revolution or 1000-revolution test window. The MIL illuminates after the fault is confirmed on two consecutive drive cycles, and the freeze frame data captured at first detection is stored in the PCM's memory for diagnostic reference.
Is It Safe to Drive?
With P0291 active, your engine or transmission is not operating within design parameters. Short-term driving may seem fine, but internal damage is accumulating — particularly to defective cyl 11 fuel injector.
Mechanic's Pro Tip
Module replacement should always be the last resort for P0291 after exhaustively verifying all power supply circuits, ground connections, and communication bus wiring. Use a wiring diagram to locate all fuses, relays, and ground points for the affected module, and measure voltage drop on each ground with the circuit loaded. A module "failure" is frequently a corroded ground eyelet or a weak battery causing brownout conditions — fix these first and you'll save hundreds of dollars on an unnecessary module replacement.
Injector replacement: 200 - 500