P28A7

Code

Generic P — Powertrain

Cylinder 6 Ion Current Sense Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 19 EN: 31 RU: 21

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Page language: EN

Causes

Short to battery/ignition supply on the ion‑sense wiring for cylinder 6
Damaged or leaking insulation on ignition coil, spark plug or harness (causing unintended conduction)
Faulty ignition coil or ion sensing element for cylinder 6
Corroded/loose connector or poor ground at cylinder 6 circuit
Internal ECM driver/amplifier failure for the ion sense channel
Carbon tracking, oil/fuel fouling or conductive deposits on spark plug or coil boot

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Possible misfire or rough idle focused on cylinder 6 (may store misfire codes)
Reduced engine performance, hesitation or stumble under load
Elevated emissions or failed readiness/inspections
Intermittent or persistent fault stored for cylinder 6 ion sensor

What to check

Read DTCs with a capable scan tool; record freeze frame and any related codes (e.g., misfire, ignition coil codes)
Monitor live ion-sensing or cylinder-specific combustion data if available; compare cylinder 6 to other cylinders
Visually inspect ignition coil, spark plug, coil boot and wiring on cylinder 6 for damage, oil, carbon, or moisture
Check connectors for corrosion, bent pins, and secure mating; wiggle test while monitoring code/data
Swap ignition coil (or coil pack) from cylinder 6 to another cylinder and see if the code follows the coil (if safe/possible)
Measure continuity and resistance of the ion sense wiring to ECU and to chassis ground; check for shorts to battery/ignition supply

Signal parameters

Ion-current signal is a low‑level pulsed waveform synchronized to ignition/combustion events; amplitude and polarity vary with design
Normal amplitude is typically small (millivolt to low-volt level) and returns to a defined idle/reference between events — consult manufacturer specification
Circuit-High condition means the sensed voltage is above the expected upper threshold (may be held near battery/ignition voltage or stuck at a constant high level)
Check for continuity to the ECM reference and for unexpected voltage on the signal lead (e.g., battery voltage, ignition feed)

Diagnostic algorithm

Retrieve and record DTC P28A7 plus any related codes and freeze-frame data. Note when the fault occurs (hot/cold/start/run).
Visually inspect cylinder 6 ignition components (coil, boot, plug) and the wiring harness and connectors for damage, oil, carbon deposits or corrosion. Repair obvious damage.
With the key off, disconnect the coil/ion-sense connector and inspect pins. Repair/clean/replace connector as required.
If safe, swap the ignition coil (and boot) between cylinder 6 and a known-good cylinder. Clear codes and run to see if the DTC follows the coil (if it does, replace coil).
Back-probe the ion-sense signal with scope or DMM during cranking/run. Look for proper pulsed waveform on other cylinders and compare to cylinder 6. If cylinder 6 is stuck high, investigate wiring for short to battery/ignition supply.
Check continuity/resistance from the coil ion-sense terminal to the ECM pin; check for short to battery and short to ground. Repair any short/open found.
Inspect/replace spark plug and coil boot if fouling or carbon tracking is present; ensure correct plug gap and torque.
If wiring and ignition hardware test good, consider ECM/driver failure — verify with manufacturer diagnostics and vehicle-specific tests; reprogram or replace ECM only after exhausting other causes.
After repairs, clear codes and perform a test drive and/or extended monitoring to confirm the fault is resolved.

Likely causes

Short to battery or constant voltage on the ion sense lead for cylinder 6
Faulty ignition coil (internal insulation breakdown) on cylinder 6
Contaminated or damaged spark plug/boot causing conductive path
Connector corrosion or pin damage at the coil/ECM harness

Fault status

⚠️ Status

P28A7 — Cylinder 6 Ion Current Sense Circuit High: ion-sense signal for cylinder 6 is above the expected range. Check ignition coil, plug, wiring, connectors and ECM driver for faults.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours