Faulty fuel injector for cylinder 10 (clogged, leaking, or electrically failed); Ignition system problem on cylinder 10, such as a worn spark plug, coil, or plug wire; Vacuum leak affecting the intake runner for cylinder 10; Mechanical issue like low compression, worn rings, or a faulty valve in cylinder 10; Exhaust leak before the oxygen sensor that skews the balance test; Contaminated fuel or fuel pressure issue affecting that cylinder

DTC codes / P23xx · Ignition system and misfire / P231D

P231DCylinder 10 Air-Fuel Ratio Imbalance Adjustment At Limit During Balance

P231D indicates that the powertrain control module (PCM) has reached the limit of its ability to balance the air-fuel ratio on cylinder 10 during a diagnostic balance test. The PCM monitors crankshaft speed variations to detect an imbalance and adjusts fuel delivery to that cylinder; when the adjustment can no longer compensate, it sets this code.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaIgnition system and misfire

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Rough idle or a noticeable vibration, especially when the engine is cold
Misfire-like shudder or hesitation during acceleration
Reduced fuel economy due to the engine running rich or lean on one cylinder
In some cases, a slight loss of power or sluggish response

Common causes, most likely first

Faulty fuel injector for cylinder 10 (clogged, leaking, or electrically failed)
Ignition system problem on cylinder 10, such as a worn spark plug, coil, or plug wire
Vacuum leak affecting the intake runner for cylinder 10
Mechanical issue like low compression, worn rings, or a faulty valve in cylinder 10
Exhaust leak before the oxygen sensor that skews the balance test
Contaminated fuel or fuel pressure issue affecting that cylinder

How to diagnose and fix it

Perform a visual inspection of the engine bay for vacuum leaks, damaged wiring, and loose connectors
Swap the ignition coil and spark plug from cylinder 10 with a known-good cylinder to see if the misfire moves
Use a scan tool to check for pending or stored misfire codes and freeze-frame data to confirm the affected cylinder
Run a compression test and cylinder leak-down test to rule out mechanical problems
Test the fuel injector for cylinder 10 with a noid light and measure its resistance; compare to specifications
Check fuel pressure and inspect for contaminated fuel if other cylinders are also affected
If all else fails, perform a crank sensor variation learn procedure or reflash the PCM as per manufacturer's instructions

Cylinder 10 balance faults often misdiagnosed

A clogged or failing fuel injector is the most common cause, but many technicians replace the ignition coil first without testing the injector.
The code can be set by a vacuum leak at the intake manifold gasket that affects only one cylinder, which is easy to overlook during a visual inspection.
Low compression from a worn camshaft lobe or a sticking valve can cause this code without triggering a traditional misfire code.
An exhaust leak upstream of the oxygen sensor can skew the air-fuel ratio readings and cause the PCM to set this balance code even when the engine is mechanically sound.
Always check for technical service bulletins (TSBs) for the specific vehicle, as some manufacturers have updated software or revised injector part numbers to address this issue.

Can I keep driving with P231D?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing. Prolonged driving with this code can damage the catalytic converter and worsen fuel economy.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.