P289A: Cylinder 3 Ion Current Sense Circuit Low

Ion current from cylinder 3 is below the expected window. Spark plug fouled, signal wire shorted to ground, or sensing path interrupted.

Medium severity. Can I keep driving?If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.

Cylinder 3 is numbered according to the manufacturer: check your engine's manual before working on it.

Most likely causes

Spark plug fouled with carbon or oil
Sense wire shorted to ground
Connector pins corroded - high contact resistance

What to check, in order

Start with the simplest. You can tick off each step.

Check the battery, connectors, and wiring
With the connector unplugged, check whether the signal wire is making contact with ground.
Read the live data with a scanner
Follow the manufacturer's service manual

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P289A means

P: Powertrain: engine and transmission
2: Generic code: same on every make
8: Transmission
9A: Specific fault in that system

Frequently asked questions

Can I keep driving with code P289A?

If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.

What causes code P289A?

The most common causes are: spark plug fouled with carbon or oil; sense wire shorted to ground; connector pins corroded - high contact resistance.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.