Code
P1228
CADILLAC
P — Powertrain
Injector Circuit Cylinder 3 Intermittent
AI status
Completed
Completed
100%
Causes
- Damaged or corroded injector connector or wiring harness (open, short to ground or battery, intermittent contact)
- Faulty fuel injector (internal coil failure or intermittent short)
- Loose, corroded, or weak power supply (fused B+) to the injector rail
- Poor or intermittent ECM/PCM driver output or damaged driver transistor
- Poor engine/chassis ground or connector pin push-out
- Water intrusion or contamination in connector
Symptoms
- Check Engine Light (MIL) illuminated (intermittent)
- Stored P1228 and possibly related injector or misfire codes (P0203, P0303)
- Intermittent rough idle or misfire felt at low loads
- Occasional hesitation, stumble or reduced power when the fault occurs
- Difficult-to-reproduce drivability complaint (fault is intermittent)
What to check
- Read freeze frame and full code list; note any additional injector, misfire, or voltage codes
- Visually inspect injector #3 connector, pins and wiring for corrosion, damage, or looseness
- Check for secure injector rail B+ feed and relevant fuses/relays (key ON engine OFF voltage)
- Measure injector coil resistance and compare to other cylinders and factory spec
- Back-probe injector connector while cranking/running with a noid light or oscilloscope to confirm pulse
- Wiggle test harness while monitoring for code reappearance or signal dropouts
Signal parameters
- Injector supply (B+) at connector with key ON: approx battery voltage (~12 V)
- Injector coil resistance: typical ranges vary by injector design — high‑impedance ~10–18 Ω, low‑impedance ~2–6 Ω; consult service data for exact spec
- Injector drive: pulse to ground from ECM. When energized the control pin will switch between ~0 V (ground) and near B+; pulse width varies with engine load
- Noid light should flash when engine cranks/runs if control signal is present; oscilloscope waveform should show clean square pulses without excessive noise or voltage drop
Diagnostic algorithm
- Confirm P1228 is current or historic; clear codes and attempt to reproduce. Capture freeze frame and conditions when code sets.
- Perform a visual inspection of injector #3 wiring and connector for corrosion, pin damage, bent pins, or water intrusion. Repair any mechanical faults.
- Check fuses/relays and verify B+ supply to the injector rail. Measure voltage at the injector supply pin (key ON, engine OFF).
- Measure the resistance of injector #3 (with connector disconnected) and compare to other injectors and service specification. Replace if out of spec or intermittent.
- Back-probe the injector control (signal) pin with a noid light while cranking/running to confirm the ECM is commanding the injector. If noid light pulses, the driver is sending a signal.
- If noid light is inconclusive, use a lab scope to inspect injector waveform for missing pulses, slow edges, high resistance, or noise. Look for intermittent drops or shorts during wiggle test.
- Perform a wiggle test on the harness and connector while monitoring live data and look for intermittent code setting or waveform change. Repair wiring harness as necessary.
- Swap injector #3 with another cylinder’s injector (if identical and safe) and observe whether the fault or misfire follows the injector. If it follows, replace injector; if it stays on cylinder 3, suspect wiring/ECM.
- Check continuity and resistance between the injector control pin and the ECM connector pin. Repair any short or open found in the circuit.
- If wiring and injector check good, inspect ECM connector pins and grounds. Consider ECM replacement only after all wiring and injector causes are eliminated; consult manufacturer TSBs and reprogramming requirements.
Likely causes
- Faulty or loose connector at injector #3 (mechanical corrosion or push-out)
- Broken/shorted wiring between injector #3 and ECM (intermittent contact when engine moves)
- Faulty injector coil (intermittent internal electrical failure)
- Weak/poor B+ feed or blown/partially blown fuse for injectors
- ECM driver circuit intermittent fault (less common)
Fault status
Status
Injector Circuit Cylinder 3 Intermittent — ECM detected an intermittent electrical fault in the fuel injector circuit for cylinder 3. This may be caused by wiring/connector issues, injector failure, or an intermittent ECM driver problem. Intermittent faults may not always produce a continuous misfire but can trigger MIL and stored diagnostic data.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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