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Severity: Moderate Code type: Generic (all makes)

P219A Code: Bank 1 Air-Fuel Ratio Imbalance

One cylinder on bank 1 runs clearly richer or leaner than the others, even if the average looks fine.

At a glance

Severity: 3/5 – Moderate3/5

Severity: Moderate

Meaning
Bank 1 Air-Fuel Ratio Imbalance
System
Fuel & Air Metering · Powertrain
Safe to drive?
With caution
Typical repair cost
$100–$1,400
DIY difficulty
Moderate

Ordinary fuel trim only looks at the average mixture of a bank. The air-fuel ratio imbalance monitor, required on newer US vehicles and widely used by GM, Toyota, Ford and Honda, looks for one cylinder that doesn't match its neighbors. When a single cylinder runs rich or lean, the upstream air-fuel sensor sees a repeating pulse at each engine cycle instead of a smooth signal, and some systems confirm it with small crankshaft speed variations. P219A means that pattern has exceeded the limit on bank 1. Because the average can still be close to stoichiometric, trims may look almost normal, which is why this code is often misdiagnosed as a bad oxygen sensor. The real cause is usually one injector, an intake leak at a single runner, or a valve that isn't opening or sealing properly.

Can I keep driving? The car is usually drivable, but one cylinder is running off its target, which raises emissions and can lead to misfires and converter damage if it gets worse. Get it diagnosed soon, and stop driving if the check engine light starts flashing.

How to read P219A

How to read P219AP122139A4
  1. P Powertrain
  2. 2 Generic (SAE)
  3. 1 Fuel & air metering
  4. 9A Specific fault

Symptoms

  • Check engine light, often with no drivability complaint
  • Slight shake at idle that you feel more than hear
  • Occasional misfire codes on one cylinder
  • Small drop in fuel economy
  • One spark plug looking different from the rest

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. One injector restricted by deposits or leaking (port or direct injection) 32%
  2. Intake leak at a single runner: port gasket, runner flap seal, cracked runner 18%
  3. Valve problem on one cylinder: carbon on the intake valve, poor seating, worn cam lobe or lifter 14%
  4. EGR passages clogged so exhaust gas reaches some cylinders more than others 10%
  5. High resistance in one injector's wiring or connector 8%
  6. Weak spark on one cylinder leaving unburned oxygen in its exhaust pulse 8%
  7. Slow or aged upstream air-fuel sensor exaggerating normal variation 6%
  8. Fuel deposits affecting all injectors unevenly 4%

Diagnosis step by step

Diagnostic flow: P219A1Check misfire counters and Mode 62Run a cylinder contribution test3Injector balance test4Swap the suspect injector5Smoke the runners and testcompression

  1. Check misfire counters and Mode 6

    Look at per-cylinder misfire counts in Mode 6 or the misfire PIDs, even if no misfire code is stored. A cylinder with a steadily higher count than the rest is your first suspect; some vehicles also list the imbalance test result in Mode 6.

    Tools: OBD-II scanner

  2. Run a cylinder contribution test

    If your scan tool can disable injectors one at a time, compare the rpm drop for each cylinder at a warm idle. A healthy engine drops about the same amount for every cylinder; one that drops much less isn't pulling its weight.

    Tools: OBD-II scanner

  3. Injector balance test

    With a fuel pressure gauge installed, pulse each injector for the same time and record the pressure drop. On port-injected engines the drops should be within roughly 10% of the average; one outlier is restricted (small drop) or over-flowing (large drop).

    Tools: Fuel pressure gauge, OBD-II scanner

  4. Swap the suspect injector

    Move the suspected injector to another cylinder on the same bank and clear codes. If the misfire count or contribution problem follows it, the injector is the fault; if it stays with the cylinder, look at the intake runner, valves and compression.

    Tools: OBD-II scanner, Screwdriver

  5. Smoke the runners and test compression

    Smoke-test the intake with special attention to each runner's gasket and flap shaft. Then do a compression and leak-down test on the suspect cylinder; a borescope through the intake port shows carbon build-up on direct-injection intake valves.

    Tools: Smoke machine, Compression tester

Where the parts are

Ignition: coils and spark plugs per cylinder – P219A1234567
Ignition: coils and spark plugs per cylinder
  1. 1Ignition coil
  2. 2Spark plug
  3. 3Fuel injector
  4. 4Camshaft sensor
  5. 5Crankshaft sensor
  6. 6Engine computer (ECM)
  7. 7Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Professional injector cleaning service No $100–$250
Replace one port fuel injector Yes $150–$400
Replace direct injector(s) with new seals No $350–$1,400
Replace intake manifold gasket No $250–$700
Walnut-blast intake valve carbon (DI engines) No $400–$800

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Field data

Honda 35 Odyssey, Pilot, Fit
Ford 5 Focus Bev, Explorer, Fusion Energi
Toyota 4 Corolla, RAV4
Ram 3 1500 Quad, 2500
Jeep 2 Renegade, Wrangler

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Emissions / smog test impact

Will fail

With the check engine light on, P219A fails the OBD-II emissions test. After repairs the imbalance monitor needs steady cruise driving to rerun, so allow a few days before the smog check.

Frequently asked questions

My fuel trims are normal. How can there be an air-fuel problem?

Trims show the average of all cylinders on the bank. One cylinder 20% lean and the others slightly rich can average out to nearly zero, and only the imbalance monitor, which looks at the shape of the sensor signal, catches it.

Will replacing the air-fuel sensor fix P219A?

Rarely. The sensor is detecting a real difference between cylinders. Replace it only after the injectors, intake runners and valves check out and the sensor is proven slow.

Will a bottle of injector cleaner help?

It can if a mildly restricted port injector is the cause, and it's cheap to try. It won't fix a leaking injector, an intake leak or carbon on direct-injection intake valves, which fuel never touches.

Why do I only get P219A and not a misfire code?

An imbalanced cylinder usually still fires. It just burns a mixture that's off target, so the crank speed stays within the misfire limit while the air-fuel sensor catches the uneven exhaust pulses.

Sources