P28AA

Code

Generic P — Powertrain

Cylinder 7 Ion Current Sense Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 17 EN: 20 RU: 19

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Page language: EN

Causes

Open or short in cylinder 7 ion-sense wiring or connector
Corroded/poor connector or pin contact at coil, harness, or ECM
Failed ignition coil (cylinder 7) or coil-to-sensor integrated module
Bad or fouled spark plug in cylinder 7
Weak/no spark due to secondary ignition fault
Mechanical combustion problem in cylinder 7 (low compression, valve issue)

Symptoms

Malfunction indicator lamp (MIL) illuminated
Cylinder 7 misfire or rough running under load or idle
Reduced engine power, hesitation or stumble
Poor fuel economy and increased emissions
Hard start or intermittent starting issues
Occasional or consistent misfire code(s) for cylinder 7 (may appear with P0307)

What to check

Read freeze frame and stored data with a scan tool; note related codes (e.g., misfire P0307, coil circuit P0357)
Observe live ion-current or combustion-detection data for cylinder 7 and compare to other cylinders
Visually inspect wiring harness, connector, and pins for corrosion, damage, or loose connector at coil and ECM
Swap coil from cylinder 7 with another cylinder and see if the code or symptom follows the coil
Check spark plug condition, gap, and resistance; replace if fouled or damaged
Inspect and test fuel injector operation for cylinder 7 (nozzle spray, resistance, pulse)

Signal parameters

System dependent; ion-current sensing often yields short combustion-correlated pulses rather than steady DC. Typical expectations: a measurable ion-current pulse or a voltage-level swing during/after ignition event.
Nominal ion-current amplitude varies by manufacturer (often microamp-level current or small voltage pulses). A “low” fault means the measured pulse amplitude or energy is below the ECM detection threshold (near zero or flatline)
When using oscilloscope: look for repeatable combustion-synchronous pulses on cylinder 7 that match other cylinders. Absence or significantly reduced amplitude indicates fault.

Diagnostic algorithm

Use a scan tool to confirm P28AA and capture freeze-frame/live data; note any related DTCs (P0307, P0357, etc.).
Visually inspect wiring/connectors at cylinder 7 coil, spark plug boot, injector harness, and ECM connector for corrosion, damage, or loose pins. Repair any obvious faults.
Swap the ignition coil (and/ or ion-sensing module if separate) from cylinder 7 with a known-good cylinder. If the code/symptom moves, replace the coil/module.
Inspect and/or replace the spark plug on cylinder 7. Check plug gap and plug condition for fouling or damage.
Check fuel injector for cylinder 7: resistance, electrical pulses with a scope or noid light, and proper spray pattern. Repair/replace injector as needed.
Measure ion-sense signal with an oscilloscope at the coil/ion-sense connector while cranking/running; compare waveform and amplitude with a known-good cylinder. If waveform absent or extremely low, focus on coil/spark/plugs and wiring.
Perform a compression or leak-down test on cylinder 7 to rule out mechanical causes that prevent ionization (low compression, valve or head gasket issues).
Test wiring continuity from coil/ion-sense connector to ECM and check for short to ground or other circuits; repair wiring if out of spec.
If wiring, coil, plug, injector, and compression are good and the signal is still low, consider ECM input fault. Verify ECM grounds/power and consult manufacturer technical bulletins before replacing ECM.
After repairs, clear codes and re-check live data and road test to ensure P28AA does not return.

Likely causes

Loose/corroded connector at ignition coil or ECM for cylinder 7
Broken insulation/short to ground on ion-sense wire near engine or harness chafe point
Failed ignition coil pack or module on cylinder 7
Worn, fouled, cracked, or incorrect spark plug in cylinder 7
Low cylinder compression (rings, valves, head gasket) preventing ionization
Seized/blocked or electrically shorted fuel injector for cylinder 7

Fault status

⚠️ Status

P28AA — Cylinder 7 Ion Current Sense Circuit Low. The ECM has detected that the ion-current (combustion detection) signal from cylinder 7 is below the expected threshold. The condition may be caused by wiring/connectors, ignition components, fuel delivery, mechanical issues, or ECM input failure. Further diagnosis required.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours