Powertrain, generic (extended)

P289D Cylinder 4 Ion Current Sense Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P289D is a rationality fault: cylinder 4 supplies an ion trace that is electrically present but not credible, for instance a combustion peak far smaller than the others at equal load, or erratic changes between cycles. Low-pass filtering of this trace gives the combustion information, band-pass filtering the knock content, so a distorted signal degrades both functions for cylinder 4. On the 2009 Saab module, the cylinder 4 ion input is pin 15 and it is combined with cylinder 2 into the second combustion signal. Wear or fouling of the plug, an oil-wetted plug well, or a genuine mixture or compression problem in cylinder 4 are typical triggers. No manufacturer publicly documents P289D; P289C, P289E and P289F cover the electrical faults.

Likely causes

Worn or fouled spark plug in cylinder 4
Oil in the plug well of cylinder 4 from a leaking cover gasket
Mixture or compression problem in cylinder 4

Symptoms

  • MIL, sometimes accompanied by P0304
  • Noticeable vibration at idle
  • Fuel consumption rises slightly

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–450
Time0.3–2 h

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

Parts involved

spark plug cyl 4ignition coil cyl 4ion sense module

Related codes

P289CP289EP289FP2899P0304

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