Faulty fuel injector for cylinder 2 (clogged, leaking, or stuck open/closed); Vacuum leak at the intake manifold runner or injector O-ring specific to cylinder 2; Worn or fouled spark plug or ignition coil for cylinder 2 causing incomplete combustion; Mechanical issue such as low compression, worn rings, or valve problem on cylinder 2; Contaminated engine oil or fuel affecting injector performance; Faulty oxygen sensor (upstream or downstream) providing skewed feedback to the ECM; Exhaust leak near the cylinder 2 port affecting the oxygen sensor reading

DTC codes / P23xx · Ignition system and misfire / P230B

P230BCylinder 2 Air-Fuel Ratio Imbalance Adjustment At Limit During Balance

P230B indicates that the engine control module (ECM) has detected an air-fuel ratio imbalance on cylinder 2 that has reached the limit of its adaptive correction during a balance test. In plain terms, the computer tried to equalize cylinder 2's power contribution by adjusting fuel delivery, but the adjustment hit its maximum allowed value, meaning the cylinder is running significantly richer or leaner than the others.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Rough idle or engine vibration, especially when cold
Slight misfire or hesitation during acceleration
Decreased fuel economy
Elevated hydrocarbon (HC) or carbon monoxide (CO) emissions on a smog test
In rare cases, a flashing check engine light if the imbalance triggers a misfire severe enough to damage the catalytic converter

Common causes, most likely first

Faulty fuel injector for cylinder 2 (clogged, leaking, or stuck open/closed)
Vacuum leak at the intake manifold runner or injector O-ring specific to cylinder 2
Worn or fouled spark plug or ignition coil for cylinder 2 causing incomplete combustion
Mechanical issue such as low compression, worn rings, or valve problem on cylinder 2
Contaminated engine oil or fuel affecting injector performance
Faulty oxygen sensor (upstream or downstream) providing skewed feedback to the ECM
Exhaust leak near the cylinder 2 port affecting the oxygen sensor reading

How to diagnose and fix it

Scan all stored codes and freeze-frame data to confirm P230B is the primary fault and not a secondary code.
Perform a visual inspection of cylinder 2 ignition components (spark plug, coil, wiring) and replace any worn or damaged parts.
Check fuel injector operation with a noid light or injector balance test; clean or replace the injector if faulty.
Conduct a compression test and cylinder leak-down test to rule out mechanical problems.
Smoke-test the intake system for vacuum leaks, paying close attention to cylinder 2 intake runner and injector seals.
Verify oxygen sensor operation with a scan tool graphing live data; replace sensors only if they fail voltage or response tests.
Clear codes and perform a drive cycle to confirm the repair; recheck for pending codes after a test drive.

What the balance test really reveals

The balance test is often run only under specific conditions (e.g., idle, closed-loop), so a cylinder that passes at idle may still fail under load; always test under the conditions that set the code.
A P230B can be set by a lazy oxygen sensor that responds slowly, causing the ECM to overcorrect fuel trim for cylinder 2 even when the injector and ignition are fine.
Mechanical faults like a slightly burned valve can cause an imbalance that only shows up when the engine is hot; a cold compression test may look normal.
After repairs, the ECM may need to relearn the balance strategy; clearing codes and completing a full drive cycle is essential before assuming the fix failed.
This code is often misdiagnosed as a simple misfire; however, P230B specifically points to fuel trim correction at its limit, so chasing ignition parts alone can waste time and money.

Can I keep driving with P230B?

You can usually drive with P230B, but avoid heavy acceleration or towing until it is diagnosed, because a persistent imbalance can overheat the catalytic converter and cause costly damage. If the check engine light flashes, stop driving and seek service immediately.

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.