🚨 Diagnostic Profile
- Vehicle/Equipment Make: CADILLAC
- Technical Description: Injector Circuit Cylinder 3 Intermittent
P1228 is a Powertrain code monitored by the Engine Control Module (ECM) or Powertrain Control Module (PCM). This code sets when the PCM detects an intermittent open or short condition in the fuel injector driver circuit for cylinder 3. The PCM commands the injector to fire by grounding or pulsing the injector control circuit at precise intervals; if the feedback voltage signal from that circuit momentarily drops out, spikes, or fails to match the expected waveform during normal engine operation, the PCM logs this intermittent fault. Common causes include a corroded or loose connector pin at the injector harness, a chafed wire rubbing against an engine bracket, a failing injector driver inside the PCM, or a solder crack within the injector itself causing erratic resistance. Because the fault is intermittent, it may not be present during every key cycle, which often results in the Check Engine Light illuminating and then going out after a drive cycle passes without the fault recurring, only for it to return under vibration, heat cycling, or specific engine RPM.
🚨 Repair Difficulty Tier
- Difficulty Rating: Intermediate
This repair requires a capable scan tool to monitor live injector pulse-width data and freeze frame conditions, along with a digital multimeter to perform resistance and voltage drop testing on the injector circuit. While an experienced DIYer with wiring diagram access can trace and repair this, the intermittent nature of the fault often demands patience and may require professional-grade oscilloscope diagnostics if basic testing does not reveal the root cause.
🛠️ Resolution Steps
- Step 1: Preliminary Inspection
Visually inspect the cylinder 3 injector electrical connector for corrosion, bent pins, or a loose locking tab. Follow the harness from the injector back toward the engine harness connector at the PCM, checking for chafe points near the intake manifold, valve cover, or any sharp edges where the insulation could be worn through. Wiggle the harness at idle while watching for the Check Engine Light to flicker or for a scan tool to show a sudden misfire count increase on cylinder 3. - Step 2: Diagnostic Verification
With the key off, disconnect the injector connector and measure resistance across the injector terminals, comparing it to factory specification (typically 11-16 ohms for most Cadillac port or direct injection units). Reconnect the injector and back-probe the control wire with a multimeter or oscilloscope while cranking or running the engine to verify a clean 0V to 12V (or 5V reference, depending on system) square wave pulse without dropouts. Use the scan tool to monitor Injector Pulse Width and Misfire Counter PIDs for cylinder 3 specifically, and perform a wiggle test on the harness and PCM connector to try to recreate the intermittent fault. - Step 3: Resolution & Reset Process
If resistance or voltage signal drops out during the wiggle test, repair or replace the damaged wiring section using solder and adhesive-lined heat shrink, or replace the connector with a factory pigtail kit if the terminals are corroded or spread. If the injector itself tests out of specification or shows an unstable circuit at the injector body, replace the injector. After repairs, clear the code using the scan tool, perform a full drive cycle incorporating idle, acceleration, and highway speeds, and confirm no new misfire or injector codes return to verify the intermittent fault has been resolved.
📦 Parts, Labor, and Budget Estimates
- Required Components/Software: OEM fuel injector (if faulty), injector harness pigtail connector kit, dielectric grease, digital multimeter, scan tool with live data capability
- Average Component Price: $45 – $220 USD (connector repair on the low end, full injector replacement on the high end)
- Estimated Labor Hours: 0.5 – 1.5 hours
- Total Estimated Budget: $100 – $350 USD