P28AB

Code

Generic P — Powertrain

Cylinder 7 Ion Current Sense Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 19 EN: 34 RU: 20

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Page language: EN

Causes

Short to battery/ignition supply on ion-sense wiring for cylinder 7
Damaged or degraded ignition coil (secondary) or coil pack for cylinder 7
Corroded, bent or contaminated connector or spark plug/ignition lead at cylinder 7
Plug or well contaminated with oil, coolant or conductive deposits
Short inside harness or pin pushed out causing high voltage on sense line
ECM/PCM internal fault or incorrect software/calibration

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Misfire symptoms on cylinder 7 (rough idle, stumble, reduced power)
Reduced fuel economy and drivability issues
Possible multiple misfire codes or misfire count increase
Engine starting or idle instability if severe

What to check

Read stored codes and freeze-frame data; note engine conditions when code set
Visually inspect coil, spark plug, boot, and wiring at cylinder 7 for damage, contamination or corrosion
Compare ion-sense live data (or secondary ignition waveform) for cylinder 7 versus other cylinders with a scan tool/oscilloscope
Inspect connector pins for pushed-out, bent, or burned terminals and secure mating
Check for aftermarket ignition parts or recent repairs that could affect the circuit
Verify proper engine grounds and battery/charging system voltage

Signal parameters

Signal type: pulse synchronized with ignition event (secondary ignition/ion current waveform)
Typical amplitude: ion currents are small (microamp to low milliamp range) and may be converted to a voltage within 0–5 V by ECU hardware (refer to OEM service data for exact values)
Abnormal condition: sustained higher-than-normal DC offset or unusually large pulse amplitude compared with other cylinders
Timing: signal should coincide with ignition event for cylinder; frequency equals engine RPM/number of ignition events

Diagnostic algorithm

Record all related DTCs and freeze frame data. Clear codes and attempt to reproduce.
Visual inspection: remove coil/boot on cylinder 7. Check spark plug, well, coil secondary and connector for carbon tracking, oil, coolant, or physical damage.
Swap coil (and ignition lead if separate) from cylinder 7 with a known-good cylinder. If code moves to the new cylinder, the coil/lead is likely defective.
Using a scan tool or oscilloscope, compare ion-current/secondary ignition waveforms for cylinder 7 vs other cylinders at idle and under load; look for higher DC offset or abnormal amplitude.
Backprobe the ion-sense signal connector and check for short to battery (VBatt) or continuous voltage present when it should be pulsed/low. Repair any shorted conductors.
Inspect and test wiring continuity and insulation between coil and ECM. Repair damaged wiring, replace connectors or pigtails as needed.
Replace spark plug, boot, or coil if contamination or defect is found. Use OE-specified parts for ion-sensing systems.
If wiring, connectors, coil and plug check good, consider ECM fault; verify correct software/calibration and consult OEM service data before ECM replacement.
After repairs, clear codes and perform road test and re-scan to confirm the issue is resolved.

Likely causes

Faulty ignition coil or coil pack on cylinder 7
Short to battery/ignition voltage on the ion-sense circuit or connector
Contaminated spark plug/boot creating conductive path and raising ion current
Damaged wiring harness or connector to cylinder 7 ion-sense pin

Fault status

⚠️ Status

Cylinder 7 Ion Current Sense Circuit High — ion-sense signal above expected threshold (possible short to voltage, contamination, or component/wiring fault).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours