Code
P1200
GWM
P — Powertrain
- Injector control circuit
Views:
UK: 11
EN: 26
RU: 9
AI status
Completed
Completed
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Causes
- Open or shorted injector wiring harness
- Poor or corroded injector connector contact
- Blown fuse or faulty relay supplying injector rail or ECM
- Failed fuel injector (electrical fault)
- Faulty ECM/PCM driver transistor or internal short
- Water/contamination at connectors
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Rough idle or misfire on one or more cylinders
- Poor acceleration or reduced power
- Hard start or no-start condition
- Increased fuel consumption or black smoke
- Intermittent loss of power correlated to vibration or movement
What to check
- Retrieve freeze frame and live data with a scan tool; note affected cylinder(s) and set conditions
- Confirm battery voltage and charging system health
- Visual inspection of injector harness, connectors and ECM connector for corrosion, damage, or loosened pins
- Check injector fuses and relay operation
- Measure injector coil resistance at the harness and compare to specification
- Backprobe injector connector while cranking to verify pulse signal (use Noid light or oscilloscope)
Signal parameters
- Injector coil resistance: typically 2–16 Ω (low-impedance ~2–3 Ω; high-impedance ~10–16 Ω). Check vehicle spec for exact value
- Supply voltage at injector connector (key ON): ~Battery voltage (11–14.5 V)
- Injector control waveform: square pulses from ECU (ground-side switching). Pulse width varies with load; commonly 1–10 ms
- Injector current (low-impedance types): can be several amps during activation; high-impedance types draw less
- Pulse frequency correlates to engine speed: pulses per cylinder per cycle (use scan tool RPM to calculate expected frequency)
- Noid light should flash when cranking or running; oscilloscope shows clean square pulses without excessive ringing
Diagnostic algorithm
- Use a scan tool to read DTCs and freeze-frame data. Note which injector/cylinder(s) reported and operating conditions when fault set.
- Clear codes and attempt to re-create fault while monitoring live data and injector status/PIDs.
- Visually inspect wiring, connectors, and harness routing for damage, corrosion, pinched wires, or signs of heat. Repair obvious damage.
- Verify power and ground: check fuse(s) for injector supply and engine/ECU ground points for good connection and low resistance to chassis.
- With ignition OFF, measure injector coil resistance at harness for the affected circuits and compare to specification; remove connector if necessary. Infinite = open; very low = shorted.
- Backprobe the injector connector while cranking/running using a Noid light or oscilloscope to confirm ECU is commanding injectors. Verify correct pulse shape, amplitude and frequency.
- If signal absent at injector but present at ECM pin, check continuity of wiring between ECM and injector and inspect connector pins. Repair open/shorts as needed.
- Perform a wiggle test of the harness and connectors while monitoring for intermittent changes in injector signal or DTC reappearance.
- Swap the suspect injector with a known-good cylinder (or install a known-good injector) to see if the fault follows the injector or stays with the circuit. If it follows the injector, replace injector.
- If wiring and injectors test good, test or bench-check ECM driver outputs per manufacturer procedure. Replace ECM only after confirming driver transistor failure or internal short.
- Safety notes: relieve fuel system pressure before removing injectors; disconnect battery when performing connector repairs or ECM replacement; follow manufacturer repair procedures.
Likely causes
- Damaged insulation or broken wire in injector harness at moving components
- Connector pins pushed out, bent, or corroded at injector or ECU connector
- Low or no battery supply to injector rail due to fuse/relay failure
- Injector coil shorted (low resistance) or open circuit (infinite resistance)
- ECM output stage failed (stuck open/shorted)
- Poor ground connection for engine/ECU
Fault status
Status
Injector control circuit malfunction detected (P1200). ECM logged abnormal injector driver or wiring condition. Inspection of wiring, connectors, injectors and ECM recommended.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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