P2891 indicates the engine control module (PCM) has detected an abnormal signal from the ion-current sensing circuit for cylinder 1. Ion sensing is used on some engines to monitor combustion quality by measuring electrical conductivity in the spark plug gap after ignition.
A worn, fouled, or improperly gapped spark plug can disrupt ion-current readings, leading to incorrect combustion feedback.
Corroded, frayed, or pinched wiring between the coil and PCM, or a poor connector, can cause out-of-range signals.
A failing coil may produce weak or inconsistent spark, affecting ion-current measurements used for combustion feedback.
Carbon tracking or moisture in the boot can interfere with the ion-sensing circuit’s ability to read combustion data.
Poor sealing valves or incorrect valve timing can alter combustion characteristics, impacting ion-current readings.
While uncommon, a PCM software glitch or internal circuit failure could incorrectly interpret ion-sensing signals. Verify all other causes first.
No. The PCM is rarely the root cause of this code. Most failures stem from the spark plug, coil, wiring, or connectors. Only consider PCM replacement after all other possibilities are ruled out.
Driving with this code may lead to reduced performance, misfires, or potential damage to the catalytic converter. Diagnose and repair the issue as soon as possible.
Ion-current sensing helps the PCM monitor combustion quality in real time, allowing for precise ignition timing adjustments and misfire detection. It is used in some modern engines for improved efficiency and emissions control.
Not always. While these are common causes, wiring issues, mechanical problems, or other faults can also trigger this code. Follow a thorough diagnostic process to confirm the root cause.