Powertrain, generic (extended)

P28AE Cylinder 8 Ion Current Sense Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28AE stands for an ion reading from cylinder 8 that stays too low or near zero. Either the measuring voltage never reaches the plug, because the coil's bias stage or its supply has failed, or it drains away to ground through a damaged signal wire, a wet plug well or a tracked boot. With ion sensing the plug doubles as knock and combustion sensor, so a dead reading also takes knock protection for cylinder 8 away and the engine computer tends to fall back on retarded timing. A supply fault affecting the whole module would rather appear as P28C0 to P28C2 than as a single-cylinder code. No manufacturer documents P28AE in public; an eight-cylinder ion-sensing engine is not described. P28AF is the high-side fault.

Likely causes

Water or oil in the cylinder 8 plug well
Damaged cylinder 8 signal wire shorted to ground
Bias stage of coil 8 not producing measuring voltage

Symptoms

  • MIL lit with a low ion reading for cylinder 8
  • Knock protection of cylinder 8 lost, timing retarded
  • Possible misfire report for cylinder 8

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–600
Time0.3–2.5 h

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

Parts involved

spark plug cyl 8ignition coil cyl 8ion sense module

Related codes

P28ACP28ADP28AFP28AAP28C1P0308

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