P28AD

Code

Generic P — Powertrain

Cylinder 8 Ion Current Sense Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 21 EN: 34 RU: 18

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Causes

Open, short, or high resistance in the ion current sense wiring for cylinder 8
Faulty ignition coil or coil pack for cylinder 8
Damaged or fouled spark plug or plug lead on cylinder 8
Corroded/loose connector at the coil or ECM
Contamination (oil, coolant, carbon) on ion sensing components
Faulty ECM or internal ion sensing circuitry

Symptoms

Check Engine Light (MIL) illuminated, code P28AD stored
Engine misfire (often felt at idle) or rough running
Reduced engine power or hesitation under load
Poor fuel economy
Possible difficulty starting or stumbling during acceleration
Intermittent faults that may vary with temperature or vibration

What to check

Read freeze frame and live data with a scan tool; confirm occurrence and any associated misfire counts (e.g., P0308)
Visual inspection of ignition coil, spark plug, boot, and wiring for cylinder 8 for damage, oil, carbon, or corrosion
Wiggle test connectors and wiring while monitoring live ion-sense signal or engine behavior for intermittent faults
Measure continuity and resistance of ion-sense wiring and coil primary/secondary circuits; check for shorts to ground/voltage
Compare ion-sense waveforms or signals between cylinder 8 and a known-good cylinder using an oscilloscope or manufacturer scan tool
Swap ignition coil (and optionally spark plug) between cylinder 8 and another cylinder to see if the fault follows the coil

Signal parameters

Ion current sensing produces very small current pulses synchronized to ignition/combustion events (typically in the microamp range)
Expected: distinct pulse(s) at each ignition event with amplitudes and timing consistent with other cylinders at the same RPM/load
Baseline (between events) should be near zero; no sustained DC offset or noise above expected microamp-level
Pulse frequency correlates to engine speed (RPM) and ignition events per cylinder
Significant reduction, absence, excessive noise, or DC offset in the waveform indicates range/performance fault

Diagnostic algorithm

Retrieve freeze frame and confirm code P28AD is current. Note engine conditions when code set (RPM, load, temperature, fuel trims, misfire counts).
Visually inspect coil, spark plug, boot, and harness for cylinder 8. Repair any obvious physical damage, contamination, or loose connectors.
Clear the code and attempt to reproduce. If intermittent, perform wiggle tests on the harness while monitoring live data.
Swap the ignition coil (and resistor boot/spark plug if accessible) between cylinder 8 and a known-good cylinder. If the code/item follows the coil, replace the coil.
Use a lab scope or manufacturer diagnostic tool to capture ion-sense waveforms on cylinder 8 and a reference cylinder. Compare amplitude, shape, and timing. Look for missing pulses, excessive noise, or DC offset.
Measure wiring continuity and resistance from the coil connector to the ECM and to ground; check for short to battery voltage or ground. Repair any wiring faults.
Inspect/replace spark plug if fouled or out of spec. Check plug gap and ignition secondary path (boots/wires).
If electrical tests are good and waveforms still abnormal, perform a compression/leak-down test to rule out mechanical combustion issues affecting ion current.
If all components and wiring check good, consult manufacturer ECM diagnostics; suspect ECM or internal ion-sense electronics and follow OEM procedures for module testing or replacement.
After repairs, erase codes and road-test to confirm the fault does not return; re-scan to ensure proper operation.