Code
P21A0
Generic
P — Powertrain
Cylinder 5 Air-Fuel Ratio Imbalance
Views:
UK: 21
EN: 41
RU: 23
AI status
Completed
Completed
100%
Causes
- Clogged, leaking or stuck fuel injector on cylinder 5
- Open/shorted injector wiring or poor connector/ECU driver circuit
- Intake manifold gasket or vacuum leak localized at cylinder 5
- Low compression or valve sealing problem on cylinder 5
- Faulty or contaminated air–fuel (lambda/O2) sensor or cylinder-specific A/F sensor
- Fuel delivery problem (fuel rail pressure, regulator) affecting one injector
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Rough idle or vibration, especially at idle
- Single-cylinder misfire or intermittent misfire codes (may show P0305)
- Reduced fuel economy or drivability issues under load
- Hesitation, stumble or lack of power from the engine
- Possible fuel smell if cylinder running rich
What to check
- Read and record all stored/ pending codes and freeze-frame data
- Compare live A/F (lambda) or O2 sensor data and fuel trims for affected bank/cylinder
- Check for related misfire (P0305) or injector circuit (P0205) trouble codes
- Visually inspect injector harness/connector for corrosion, loose pins, damaged insulation
- Measure injector resistance and compare with spec; inspect for carbon/fuel deposits
- Command injector on/off with scan tool or use a noid light/oscilloscope to verify pulse
Signal parameters
- O2 sensor voltage (narrowband): ~0.1–0.9 V switching; sluggish or biased readings indicate issues
- Wideband AFR: stoichiometric ≈ 14.7:1 (lambda ≈ 1.0); cylinder 5 should track other cylinders
- Short-term fuel trim (STFT): typically within ±10% per bank; large deviation on affected side is notable
- Long-term fuel trim (LTFT): should be stable and within ±10% for normal operation
- Injector resistance: vehicle-specific (typical common range 10–16 Ω); compare to spec
- Injector pulse width at idle: typically ~1–4 ms (varies by engine/load); abnormal values or no pulses indicate control/wiring fault
Diagnostic algorithm
- Retrieve freeze-frame and live data. Note A/F or O2 readings and per-bank fuel trims when code set; confirm code reproducibility.
- Scan for related codes (P0305, P0205, P0171/P0172, P0174). Address these as applicable before deeper tests.
- Visually inspect injector connector and wiring to cylinder 5. Wiggle test while monitoring injector command and response.
- Check injector supply voltage and ground, measure injector coil resistance. If resistance out of spec or intermittent, replace or bench-test injector.
- Command injector with scan tool (if supported) and confirm fuel delivery (fuel smell, fuel pressure drop, or use a flow/volume test).
- Swap the cylinder 5 injector with another known-good injector (same type) and clear codes. If the code follows the injector to the other cylinder, replace the injector.
- If swapping doesn’t move the fault, inspect and test wiring/driver circuit (noid light/oscilloscope) and check PCM driver outputs.
- Perform intake smoke test around cylinder 5 intake runner and gasket to find leaks that would cause a local lean condition.
- Perform compression and/or leak-down test on cylinder 5 to rule out mechanical sealing issues causing irregular A/F behavior.
- Check fuel rail pressure and regulator; confirm adequate static and dynamic pressure and no air in fuel.
- Inspect and test the A/F or O2 sensor(s); compare upstream/downstream sensor signals and response times. Replace if sensor readings are biased or sluggish.
- After repairs or parts replacement clear codes and road-test with live data capture to confirm cylinder 5 A/F returns to nominal and code does not recur.
Likely causes
- Faulty/inconsistent fuel injector performance (most common)
- Wiring/connector fault to injector or local sensor
- Intake manifold leak or runner gasket near cylinder 5
- Cylinder mechanical issue (compression/leakdown)
- Faulty local A/F/O2 sensor or inaccurate sensor reading
Fault status
Status
Cylinder 5 air–fuel ratio imbalance detected — PCM has recorded a persistent deviation for cylinder 5 compared with other cylinders/expected A/F values.
Repair difficulty: Medium
Diagnostic time: 1.5 - 3.5 hours
Workshop Manuals
Available brands with manuals
2
AUDI 11
6-speed manual gearbox 0B1, front-wheel drive — Workshop Manual (Edition 05.2014)
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Audi A3 (1997) – 1.6L 4-cylinder (2‑valve) Engine Mechanical Components Service Manual (AEH, AKL, APF) – Edition 07.2002
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AUDI A3 (2004) Workshop Manual — 2.0L FSI Turbo (4‑cyl, 4‑valve) Engine, Mechanics — Edition 03.2017
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Audi A3 2004 — Electrical System (Workshop Manual, Edition 02.2018)
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Audi A4 / A4 Cabriolet – 4.2 l V8 (5‑valve, timing chains) – Workshop Manual (Mechanics) – Edition 04.2007
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Audi A4 / A4 Cabriolet — Auxiliary Heater Workshop Manual (Edition 08.2004)
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Audi A4 / A4 Cabriolet (1.8T 4‑cyl turbo) — Motronic Injection & Ignition System Service Manual (Edition 01.2015)
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Audi A8 (2003) — Electrical System Workshop Manual (Edition 08.2014)
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Audi Q4 e-tron (Type F4) - Self-study Programme SSP 685
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Audi Q8 (2018) — Electrical System Workshop Manual (Edition 05.2019)
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Audi Servicing Manual — 7‑Speed Dual Clutch Transmission 0CJ / 0CL / 0CK / 0DN / 0DP / 0HL (Edition 05.2018)
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LAND ROVER 3
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop Manual199,00 UAH
Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop Manual199,00 UAH
Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop Manual199,00 UAH
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Code
P21A0
LAND ROVER
P — Powertrain
Cylinder 5 - air fuel ratio imbalance
Views:
UK: 6
EN: 7
RU: 7
AI status
Completed
Completed
100%
Causes
- Clogged, leaking or stuck fuel injector on cylinder 5
- Open/shorted injector wiring or poor connector/ECU driver circuit
- Intake manifold gasket or vacuum leak localized at cylinder 5
- Low compression or valve sealing problem on cylinder 5
- Faulty or contaminated air–fuel (lambda/O2) sensor or cylinder-specific A/F sensor
- Fuel delivery problem (fuel rail pressure, regulator) affecting one injector
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Rough idle or vibration, especially at idle
- Single-cylinder misfire or intermittent misfire codes (may show P0305)
- Reduced fuel economy or drivability issues under load
- Hesitation, stumble or lack of power from the engine
- Possible fuel smell if cylinder running rich
What to check
- Read and record all stored/ pending codes and freeze-frame data
- Compare live A/F (lambda) or O2 sensor data and fuel trims for affected bank/cylinder
- Check for related misfire (P0305) or injector circuit (P0205) trouble codes
- Visually inspect injector harness/connector for corrosion, loose pins, damaged insulation
- Measure injector resistance and compare with spec; inspect for carbon/fuel deposits
- Command injector on/off with scan tool or use a noid light/oscilloscope to verify pulse
Signal parameters
- O2 sensor voltage (narrowband): ~0.1–0.9 V switching; sluggish or biased readings indicate issues
- Wideband AFR: stoichiometric ≈ 14.7:1 (lambda ≈ 1.0); cylinder 5 should track other cylinders
- Short-term fuel trim (STFT): typically within ±10% per bank; large deviation on affected side is notable
- Long-term fuel trim (LTFT): should be stable and within ±10% for normal operation
- Injector resistance: vehicle-specific (typical common range 10–16 Ω); compare to spec
- Injector pulse width at idle: typically ~1–4 ms (varies by engine/load); abnormal values or no pulses indicate control/wiring fault
Diagnostic algorithm
- Retrieve freeze-frame and live data. Note A/F or O2 readings and per-bank fuel trims when code set; confirm code reproducibility.
- Scan for related codes (P0305, P0205, P0171/P0172, P0174). Address these as applicable before deeper tests.
- Visually inspect injector connector and wiring to cylinder 5. Wiggle test while monitoring injector command and response.
- Check injector supply voltage and ground, measure injector coil resistance. If resistance out of spec or intermittent, replace or bench-test injector.
- Command injector with scan tool (if supported) and confirm fuel delivery (fuel smell, fuel pressure drop, or use a flow/volume test).
- Swap the cylinder 5 injector with another known-good injector (same type) and clear codes. If the code follows the injector to the other cylinder, replace the injector.
- If swapping doesn’t move the fault, inspect and test wiring/driver circuit (noid light/oscilloscope) and check PCM driver outputs.
- Perform intake smoke test around cylinder 5 intake runner and gasket to find leaks that would cause a local lean condition.
- Perform compression and/or leak-down test on cylinder 5 to rule out mechanical sealing issues causing irregular A/F behavior.
- Check fuel rail pressure and regulator; confirm adequate static and dynamic pressure and no air in fuel.
- Inspect and test the A/F or O2 sensor(s); compare upstream/downstream sensor signals and response times. Replace if sensor readings are biased or sluggish.
- After repairs or parts replacement clear codes and road-test with live data capture to confirm cylinder 5 A/F returns to nominal and code does not recur.
Likely causes
- Faulty/inconsistent fuel injector performance (most common)
- Wiring/connector fault to injector or local sensor
- Intake manifold leak or runner gasket near cylinder 5
- Cylinder mechanical issue (compression/leakdown)
- Faulty local A/F/O2 sensor or inaccurate sensor reading
Fault status
Status
Cylinder 5 air–fuel ratio imbalance detected — PCM has recorded a persistent deviation for cylinder 5 compared with other cylinders/expected A/F values.
Repair difficulty: Medium
Diagnostic time: 1.5 - 3.5 hours
HTML Workshop Manuals AI manual library for LAND ROVER Click to show available manuals 1
LAND ROVER 2015 Discovery Sport HSE
HTML ManualWorkshop Manuals
Repair manuals for LAND ROVER
3
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop Manual199,00 UAH
Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop Manual199,00 UAH
Land Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop Manual199,00 UAH
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
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0
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