Powertrain, generic (extended)

P28A6 Cylinder 6 Ion Current Sense Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28A6 describes an ion reading from cylinder 6 that never leaves the bottom of its range. Between sparks the system keeps a small voltage across the plug, and the hot gas of a normal combustion lets a measurable current pass; if that voltage leaks to ground through a damaged conductor, a cracked ceramic or carbon deposits, or the coil stops supplying it, the reading collapses. With no usable value, the module treats cylinder 6 as unmonitored and usually falls back to safe timing. When tracing the fault, the harness along the cam cover deserves a close look for heat damage and chafed spots. No manufacturer documents P28A6 publicly; P28A7 is the high-side code.

Likely causes

Damaged ion conductor of cylinder 6 leaking to ground
Cracked ceramic or heavy deposits on the cylinder 6 plug
Coil 6 no longer supplies the measuring voltage

Symptoms

  • MIL with low ion signal on cylinder 6
  • Misfires on cylinder 6 possibly unrecorded
  • Engine noticeably weaker on safe timing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–550
Time0.3–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

spark plug cyl 6ignition coil cyl 6ion sense module

Related codes

P28A4P28A5P28A7P28A2P0306

References: law.cornell.edu, saabwisonline.com, en.wikipedia.org.