P28A4

Code

Generic P — Powertrain

Cylinder 6 Ion Current Sense Circuit

Brand: Generic

Type: P — Powertrain

Views: UK: 16 EN: 23 RU: 15

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Read stored codes and freeze frame data; note related codes (e.g., misfire P0306)
Check live data for misfire counters and compare cylinder contribution values
Visually inspect coil-on-plug, spark plug and wiring for damage, corrosion or oil contamination
Check connector pins for looseness, corrosion and proper mating
Perform a basic continuity/resistance check of ion sense wiring and ground connections
Swap coil from cylinder 6 with another cylinder to see if code follows the coil (if coil swap is feasible and safe)

Ion current waveform: short pulses during/after ignition event (combustion ionization)
Typical amplitude: microamp to tens of microamps (very low current) — measured as small voltage across sense resistor or on coil sense terminal
Pulse duration: a few milliseconds during combustion; waveform shape should be similar to other cylinders
Expected behavior: cylinder 6 ion signal should be present and similar in amplitude and timing to other cylinders under same conditions (within roughly ±20%)

Verify the code: read DTCs and freeze frame. Note engine operating conditions when fault occurred and any related codes (P0306 etc.).
Visual inspection: with engine off, inspect coil, spark plug well, coil harness and connector for damage, oil, coolant, loose pins or corrosion. Repair as needed.
Basic electrical checks: back-probe coil connector to check supply voltage, ground, and ion sense reference (compare to a known-good cylinder). Check continuity of the ion-sense wire to the ECM and for shorts to ground or battery.
Swap coil/plugs: swap coil-on-plug (and plug if practical) between cylinder 6 and a known-good cylinder. If the fault moves, replace the coil (or plug).
Scope the ion signal: using an oscilloscope or manufacturer diagnostic tool, capture the ion current waveform on cylinder 6 and compare to a good cylinder at idle and under load. Look for missing pulses, low amplitude or noise.
Mechanical checks: if ion signal looks valid but combustion is poor, perform a compression or leak-down test on cylinder 6 and inspect for oil or coolant intrusion.
Repair and retest: repair wiring/connectors, replace coil or plug, correct mechanical faults. Clear codes and road-test; verify no return of P28A4 and check misfire counters and emissions.
ECM checks: if all wiring, ignition and mechanical checks are normal and ion waveform is normal yet code persists, consider ECM input circuit test or replacement as a last step.

Damaged or chafed harness to cylinder 6 coil (open/short to ground or battery)
Failed coil-on-plug unit on cylinder 6
Worn, fouled or incorrectly gapped spark plug in cylinder 6
Loose or corroded coil mounting/connector or poor engine ground
Low cylinder compression, burnt valve, or oil/coolant fouling contaminating the plug/coils