Powertrain, generic (extended)

P28B1 Cylinder 9 Ion Current Sense Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P28B1 indicates that cylinder 9 produces an ion signal of believable electrical level whose shape or strength does not match engine speed, load or the neighbouring cylinders. Since the reading reflects combustion pressure and temperature, the root cause is often mechanical or mixture-related: a worn or oil-fouled plug, a leaking valve, a weak injector on cylinder 9, or condensation in the plug well. Saab used the same signal to count missing combustions per cylinder over 1000 crankshaft revolutions, the interval CARB also prescribes for emission-relevant misfire. No manufacturer documents P28B1, and engines with nine or more cylinders using ion sensing are not publicly described. P28B0, P28B2 and P28B3 are the electrical faults; P0309 may follow.

Likely causes

Worn or oil-fouled spark plug in cylinder 9
Weak spray from the cylinder 9 injector
Leaking valve on cylinder 9
Condensation in the cylinder 9 plug well

Symptoms

  • MIL, possibly with misfire code P0309
  • Noticeably uneven running at idle
  • Higher fuel consumption

Repair estimate

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

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

Parts involved

spark plug cyl 9ignition coil cyl 9ion sense module

Related codes

P28B0P28B2P28B3P28ADP28B5P0309

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