Code
P0066
Generic
P — Powertrain
Air Assisted Injector Control Circuit Low
Views:
UK: 23
EN: 45
RU: 35
AI status
Completed
Completed
100%
Causes
- Short to ground in the injector control wiring
- Open or high-resistance wiring/connector (poor contact, corrosion, broken wire)
- Failed air-assisted injector solenoid or internal short
- Low battery/poor battery condition or weak power/ground supply
- Faulty ECM or driver transistor
- Poor or missing ground at engine/chassis or ECM ground strap
Symptoms
- Check Engine Light (MIL) illuminated
- Rough idle or noticeable misfire on affected cylinder(s)
- Reduced engine power or hesitation under load
- Poor fuel economy
- Hard starting or extended cranking
- Possible limp-home mode depending on vehicle strategy
What to check
- Read stored/freeze-frame data and confirming P0066 with a scan tool; note operating conditions when fault set
- Check for additional DTCs (injector, low voltage, CAN/communication faults) that may be related
- Visually inspect injector harness and connector for damage, corrosion, water ingress or bent pins
- Measure battery voltage and charging system voltage with engine running
- Backprobe injector control connector to check voltage and signal while cranking/running
- Measure injector/solenoid coil resistance and compare to spec
Signal parameters
- Supply voltage (reference): approx. battery voltage at injector supply pin (typically ~12–14 V with engine running)
- Control/driver voltage: expected to toggle between near 0 V and battery voltage or be a low-side switched PWM depending on design
- ‘Low’ condition threshold: circuit voltage significantly lower than expected (generally below ~0.5–1.0 V on a switching driver) when inactive or when ECM expects high)
- Typical coil resistance: varies by design (commonly 0.5–5 Ω for direct injectors, up to tens of ohms for others) — check vehicle spec
- PWM frequency (if used): commonly from tens to several hundred Hz; duty cycle varies with injector control demand
Diagnostic algorithm
- Verify the code: clear DTCs, start engine, and attempt to re-create the fault while monitoring freeze-frame and live data.
- Inspect harness and connector: visually inspect the injector harness, connector, pins, and nearby wiring for damage, corrosion, or service-related pin damage.
- Check battery/charging: confirm battery and charging system voltages are within specification; correct any low-voltage conditions before further testing.
- Backprobe and observe: backprobe the injector control connector and monitor with a multimeter or oscilloscope while cranking/idle and under load to observe voltage/signal behavior.
- Measure injector coil resistance: unplug injector and measure coil resistance at the connector and compare to published specification; an open or shorted coil indicates a faulty injector.
- Wiggle test: with connector connected, carefully wiggle wiring while observing live data for intermittent changes indicating broken wires or poor contact.
- Check supply and ground: verify the injector supply power and ground circuits have low resistance to battery and chassis ground; repair any poor connections.
- Swap test (if applicable): if multiple air-assisted injectors are present and identical, swap the suspect injector with a known good one and see if the code follows the injector.
- Use oscilloscope: if available, use an oscilloscope to inspect waveform shape and switching behavior — helps distinguish driver failure from wiring/coil issues.
- Isolate ECM: if wiring and injector test good but circuit remains low, consult wiring diagrams and check continuity back to the ECM/driver. Replace ECM only after exhausting wiring and component checks.
- Re-test: after repair or replacement, clear codes and road test to confirm the fault does not return. Check for any applicable manufacturer TSBs or software updates before replacing major components.
Likely causes
- Damaged connector: corroded pins, bent pins, or pushed-out pins at the injector harness
- Wiring chafed and shorted to ground (heat, rubbing against metal)
- Injector solenoid coil failed low impedance or internally shorted
- Low battery voltage or poor main power feed to injector circuit
- ECM output driver failed and is pulling circuit low
Fault status
Status
ECM detected a low (below expected) voltage or signal on the air-assisted injector control circuit — indicates an electrical fault in the injector control wiring, connector, injector/solenoid, or ECM driver.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P0066
LAND ROVER
P — Powertrain
Circuit or control circuit of injector with low air assistance
Views:
UK: 7
EN: 24
RU: 16
AI status
Completed
Completed
100%
Causes
- Short to ground in the injector control wiring
- Open or high-resistance wiring/connector (poor contact, corrosion, broken wire)
- Failed air-assisted injector solenoid or internal short
- Low battery/poor battery condition or weak power/ground supply
- Faulty ECM or driver transistor
- Poor or missing ground at engine/chassis or ECM ground strap
Symptoms
- Check Engine Light (MIL) illuminated
- Rough idle or noticeable misfire on affected cylinder(s)
- Reduced engine power or hesitation under load
- Poor fuel economy
- Hard starting or extended cranking
- Possible limp-home mode depending on vehicle strategy
What to check
- Read stored/freeze-frame data and confirming P0066 with a scan tool; note operating conditions when fault set
- Check for additional DTCs (injector, low voltage, CAN/communication faults) that may be related
- Visually inspect injector harness and connector for damage, corrosion, water ingress or bent pins
- Measure battery voltage and charging system voltage with engine running
- Backprobe injector control connector to check voltage and signal while cranking/running
- Measure injector/solenoid coil resistance and compare to spec
Signal parameters
- Supply voltage (reference): approx. battery voltage at injector supply pin (typically ~12–14 V with engine running)
- Control/driver voltage: expected to toggle between near 0 V and battery voltage or be a low-side switched PWM depending on design
- ‘Low’ condition threshold: circuit voltage significantly lower than expected (generally below ~0.5–1.0 V on a switching driver) when inactive or when ECM expects high)
- Typical coil resistance: varies by design (commonly 0.5–5 Ω for direct injectors, up to tens of ohms for others) — check vehicle spec
- PWM frequency (if used): commonly from tens to several hundred Hz; duty cycle varies with injector control demand
Diagnostic algorithm
- Verify the code: clear DTCs, start engine, and attempt to re-create the fault while monitoring freeze-frame and live data.
- Inspect harness and connector: visually inspect the injector harness, connector, pins, and nearby wiring for damage, corrosion, or service-related pin damage.
- Check battery/charging: confirm battery and charging system voltages are within specification; correct any low-voltage conditions before further testing.
- Backprobe and observe: backprobe the injector control connector and monitor with a multimeter or oscilloscope while cranking/idle and under load to observe voltage/signal behavior.
- Measure injector coil resistance: unplug injector and measure coil resistance at the connector and compare to published specification; an open or shorted coil indicates a faulty injector.
- Wiggle test: with connector connected, carefully wiggle wiring while observing live data for intermittent changes indicating broken wires or poor contact.
- Check supply and ground: verify the injector supply power and ground circuits have low resistance to battery and chassis ground; repair any poor connections.
- Swap test (if applicable): if multiple air-assisted injectors are present and identical, swap the suspect injector with a known good one and see if the code follows the injector.
- Use oscilloscope: if available, use an oscilloscope to inspect waveform shape and switching behavior — helps distinguish driver failure from wiring/coil issues.
- Isolate ECM: if wiring and injector test good but circuit remains low, consult wiring diagrams and check continuity back to the ECM/driver. Replace ECM only after exhausting wiring and component checks.
- Re-test: after repair or replacement, clear codes and road test to confirm the fault does not return. Check for any applicable manufacturer TSBs or software updates before replacing major components.
Likely causes
- Damaged connector: corroded pins, bent pins, or pushed-out pins at the injector harness
- Wiring chafed and shorted to ground (heat, rubbing against metal)
- Injector solenoid coil failed low impedance or internally shorted
- Low battery voltage or poor main power feed to injector circuit
- ECM output driver failed and is pulling circuit low
Fault status
Status
ECM detected a low (below expected) voltage or signal on the air-assisted injector control circuit — indicates an electrical fault in the injector control wiring, connector, injector/solenoid, or ECM driver.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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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👎 Dislike
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Send to email