P231D: Cylinder 10 Air-Fuel Ratio Imbalance Adjustment At Limit During Balance

What it means

The ECU continuously trims individual cylinders to equalise air-fuel ratio across the bank using ion-current or per-cylinder lambda feedback. For cylinder 10 the per-cylinder fuel correction has hit its software-side maximum or minimum without restoring balance, indicating the underlying mechanical or fuelling deviation is too large to compensate.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The engine control module uses per-cylinder feedback to adjust fueling and balance combustion across the engine. This code means the correction for cylinder 10 has reached its adjustment limit without resolving the air-fuel imbalance, pointing to a cylinder 10 fueling or mechanical problem such as injector flow drift or low compression.

Common causes

Most likely first.

1. Fuel injector for cylinder 10 has drifted in flow rate
2. Reduced compression on cylinder 10

Symptoms

• Check-engine light
• Rough idle
• Engine hesitation or reduced power
• Increased fuel consumption

How to diagnose it

1. Record freeze-frame data and review any per-cylinder balance or fuel-correction data to confirm that cylinder 10 is the one reaching its limit.
2. Inspect cylinder 10's injector connector and wiring for looseness, damage, or corrosion.
3. Check for intake or vacuum leaks near cylinder 10 that could disturb its mixture, using the vehicle's layout to identify the relevant area.
4. Test cylinder 10's injector operation and flow against the manufacturer's procedure and compare it with other cylinders.
5. Perform a compression test on cylinder 10 and compare the result with the manufacturer's specification and the other cylinders.

Common fixes

• Repair a loose or damaged cylinder 10 injector connection.
• Correct an intake leak affecting cylinder 10.
• Clean or replace the cylinder 10 injector if testing confirms abnormal flow.
• Repair the mechanical cause if cylinder 10 compression is low.

Can I keep driving?

Short, gentle trips may be possible if the engine runs smoothly, but avoid heavy loads and arrange diagnosis soon. Stop if the check-engine light flashes or the engine runs very roughly, as a persistent imbalance can raise emissions and damage the catalytic converter.