Code
P28A6
Generic
P — Powertrain
Cylinder 6 Ion Current Sense Circuit Low
AI status
Completed
Completed
100%
Causes
- Open or short in ion-sense wiring for cylinder 6
- Poor connector contact or corrosion at the coil/plug/ECM connector
- Failed ignition coil or coil pack channel for cylinder 6
- Bad or fouled spark plug or incorrect spark plug gap
- High resistance in ground or supply circuits related to the ignition/ion-sense circuit
- Faulty ECM/ion sensing input circuitry
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Possible misfire or rough idle limited to cylinder 6
- Reduced engine performance or hesitation under load
- Difficulty starting or increased emissions
- Scan tool may show low or missing ion-current waveform for cylinder 6
What to check
- Read and record all stored DTCs and freeze frame data with a scan tool
- Verify engine conditions when code set (temperature, load, RPM, misfire counts)
- View live ion-current data or oscilloscope waveform for cylinder 6 and compare with a good cylinder
- Visually inspect coil, spark plug, harness and connectors for damage, corrosion, or oil/water intrusion
- Check connector pin continuity and resistance between coil/plug and ECM ion-sense pin
- Swap coil (or coil channel) between cylinder 6 and a known-good cylinder to see if the code follows the coil
Signal parameters
- Ion-current signal: brief pulse coincident with ignition/combustion event (measured at ECM ion input)
- Expected: distinct pulse waveform on every fired event for a healthy cylinder (baseline near zero between events)
- Low condition: absent, very small, clipped or noisy pulses compared with other cylinders
- Measurement tools: dedicated scan-tool live data or oscilloscope on ion-sense line referenced to chassis ground
Diagnostic algorithm
- Retrieve DTCs, freeze frame and live data; confirm P28A6 is current and note operating conditions when set.
- Visually inspect ignition coil, plug, harness and connectors at cylinder 6 for damage, corrosion, oil or water intrusion.
- Using a scan tool or oscilloscope, view ion-current waveform for cylinder 6 and compare to a known-good cylinder. Note presence/absence and amplitude of pulses.
- Check wiring continuity and resistance between cylinder 6 coil ion-sense terminal and the ECM input pin; inspect for shorts to ground or battery.
- Swap the cylinder 6 coil (or coil pack channel) with a known-good cylinder. Clear codes and run engine: if code follows the coil, replace coil.
- Replace or inspect spark plug for fouling, correct type and gap; retest. A fouled or damaged plug can reduce ionization.
Likely causes
- Damaged or disconnected ion-sense lead between coil and ECM
- Corroded pin or water intrusion at coil or harness connector
- Failed coil primary/secondary on cylinder 6
- Worn, fouled, cracked or incorrect spark plug in cylinder 6
- Loose or corroded ground or battery connection affecting sensing reference
Fault status
Status
P28A6 - Cylinder 6 Ion Current Sense Circuit Low
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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