Code
P21A0
LAND ROVER
P — Powertrain
Cylinder 5 - air fuel ratio imbalance
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EN: 7
RU: 7
AI status
Completed
Completed
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Causes
- Faulty or clogged fuel injector on cylinder 5
- Open/shorted wiring or poor connector at injector or coil pack
- Ignition problem on cylinder 5 (weak spark or coil failure)
- Mechanical engine issue on cylinder 5 (low compression, valve damage, piston ring/cylinder wear)
- Intake leak near cylinder 5 (port gasket, manifold) or injector seal leak
- Contaminated fuel or injector stuck open
Symptoms
- Check Engine Light (MIL) illuminated
- Rough idle or vibration, especially at idle or light load
- Reduced engine performance, hesitation or stumble under acceleration
- Increased fuel consumption or visible smoke if rich
- Misfire codes (e.g., P0305) may appear if imbalance is severe
- Failed emissions test or high tailpipe HC/CO/NOx
What to check
- Read stored codes and freeze‑frame data; note fuel trim and RPM when fault stored
- Scan live data: cylinder contribution, short‑term and long‑term fuel trims, O2/wideband sensor lambda
- Inspect wiring harness and connectors for cylinder 5 injector and coil (corrosion, broken wires, poor pins)
- Measure injector electrical resistance and compare to spec
- Use noid light or scope to verify injector pulse and coil primary waveform
- Perform compression and/or leak‑down test on cylinder 5 and neighboring cylinders
Signal parameters
- Short‑term fuel trim (STFT): normally within ±10%; significant deviation on cylinder 5 indicates local imbalance
- Long‑term fuel trim (LTFT): should trend near 0% after adaptation; large corrections (>±10–15%) abnormal
- Lambda/wideband AFR: ~1.00 lambda (stoich) under cruise; deviations at cylinder contribution point indicate imbalance
- Narrowband O2 voltage: approx 0.1–0.9 V cycling (if applicable)
- Injector resistance: consult manufacturer spec (typically tens of ohms for low‑impedance coils/injectors or higher for high‑impedance types)
- Fuel rail pressure: depends on system—verify within manufacturer tolerance and stable under load
Diagnostic algorithm
- Retrieve DTCs, freeze‑frame and live data. Confirm P21A0 and note conditions when set (RPM, load, fuel trims, temp).
- Visually inspect wiring and connectors for cylinder 5 injector and coil. Repair any damage before further testing.
- Check injector operation: measure resistance, use a noid light or oscilloscope to confirm injector pulse, and listen for injector click.
- Swap the cylinder 5 injector (and/or coil) with a known good cylinder. Clear codes and road/test. If the fault follows the component, replace it.
- Perform compression and/or leak‑down test on cylinder 5. Compare to other cylinders to identify mechanical issues.
- Inspect intake manifold gasket, injector O‑ring and surrounding area for vacuum leaks or intake air intrusion; perform smoke test if needed.
- Verify fuel system health: static and dynamic fuel pressure, look for contamination or flow restriction.
- Monitor per‑cylinder fuel trims and wideband/O2 sensor data during test drive; evaluate cylinder contribution tests if available.
- If wiring and components test normal and mechanical integrity is good, consider ECM input faults or software updates—consult manufacturer technical service info.
- After repairs, clear codes and recheck under the same conditions to confirm the issue is resolved.
Likely causes
- Faulty injector or injector wiring for cylinder 5 (most common for cylinder‑specific AFR faults)
- Ignition coil or spark plug issue on cylinder 5
- Local intake leak or leaking injector sealing O‑ring causing extra air
- Low compression or mechanical fault in cylinder 5
- Fuel delivery problems (pressure or contamination) affecting one injector
Fault status
Status
P21A0 — Cylinder 5 air/fuel ratio imbalance. The ECM has detected a persistent AFR deviation or cylinder contribution anomaly at cylinder 5. This can cause rough running, increased emissions and may indicate injector, ignition, intake sealing, mechanical or fuel delivery faults. Further testing required to identify the root cause.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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