P2894 Cylinder 2 Ion Current Sense Circuit

P2894 covers a general fault in the ion current circuit of cylinder 2: the processing electronics get no evaluable signal from this plug. Which physical position cylinder 2 occupies depends on the maker's numbering. On Saab's Trionic four-cylinder, cylinders 2 and 3 are fired together by waste spark during start-up, and only the ion signals tell the engine management which of the two actually burned; a missing cylinder 2 signal can thus prolong cranking. In the 2009 Saab 9-3 module, cylinder 2 has its own ion input and trigger line and feeds the second combustion signal together with cylinder 4. No manufacturer publishes P2894; checking coil 2, its wiring and the plug comes first, and swapping coils between cylinders shows whether the fault moves.

Likely causes

Symptoms

• MIL with a stored cylinder 2 ion fault
• Hard or longer starting in some cases
• Cautious ignition timing and slightly less power

Repair estimate

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

Parts involved

Related codes

References: law.cornell.edu, saabwisonline.com, saabwisonline.com.