Powertrain, generic (extended)

P2899 Cylinder 3 Ion Current Sense Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

With P2899 an ion signal from cylinder 3 does arrive, yet it fails the plausibility check: its amplitude is too weak for the current load, it fluctuates without reason, or it no longer matches the pattern of the remaining cylinders. Because the measurement mirrors how hot and how highly compressed the burning charge is, an actual combustion weakness in cylinder 3 can be the cause just as much as a degraded plug with a leakage path. In Saab's 2009 detection module, cylinder 3 enters on its own input and is merged with cylinder 1 into the first combustion signal, while a band-pass branch extracts knock ringing from the same raw trace. No maker documents P2899 publicly. Hard electrical faults on cylinder 3 are P2898, P289A and P289B.

Likely causes

Spark plug of cylinder 3 with deposits or excessive gap wear
Weak combustion in cylinder 3 (lean injector, low compression)
Damaged plug boot or moisture at the coil 3 connection

Symptoms

  • MIL, possibly together with P0303
  • Slight roughness at idle or under light load
  • Knock control retards timing more than usual

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–400
Time0.3–1.5 h

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

Parts involved

spark plug cyl 3ignition coil cyl 3ion sense module

Related codes

P2898P289AP289BP2895P0303

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