P28B7 Cylinder 10 Ion Current Sense Circuit High

P28B7 means the ion signal of cylinder 10 is stuck above its valid window. The usual suspects are a sense lead shorted to a supply or to a neighbouring ignition circuit, breakdown inside coil 10 that lets spark energy into the measuring path, and a poor ground at the evaluation side that shifts the reference upward. A falsely high signal could pass as continuous combustion or as permanent knock, so the engine computer typically discards it and retards timing on that cylinder for safety. Saab's later T8 module, which processes the ion signal of each coil on its own input pin, shows the cylinder-selective layout such a code assumes. No manufacturer documents P28B7 publicly. The low-side fault is P28B6, module supply problems are P28C0 to P28C2.

Likely causes

Symptoms

• MIL with high ion reading on cylinder 10
• Timing on cylinder 10 retarded for safety
• Misfire on cylinder 10 may be masked

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.