P2C28: Fuel Injector Group B Supply Sense Circuit High

What it means

Voltage on the supply sense circuit of fuel injector group B is above the expected window. Indicates overvoltage or wire shorted to B+.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

Fuel injector group B uses a shared supply feed, and the ECM checks its voltage through a sense circuit. P2C28 sets when that sensed voltage exceeds the expected range, which can result from excessive charging voltage or a sense wire shorted to battery positive.

Common causes

Most likely first.

1. Alternator regulator drift - overvoltage
2. Sense wire shorted to B+
3. Connector pins corroded - high contact resistance

Symptoms

• Check engine light on
• Misfire or rough idle on the affected cylinder
• Increased fuel consumption
• Possible fuel smell or smoke from exhaust

How to diagnose it

1. Use freeze-frame and live data to confirm the group B sense reading is high and note whether other module or charging-voltage readings are also elevated.
2. Inspect the group B sense wire and connectors for chafing against a power feed, corrosion and loose or pushed-back pins.
3. Measure vehicle charging voltage under the manufacturer's test conditions and compare it with the manufacturer's specification to check for regulator overvoltage.
4. With power off as directed by the manufacturer, test the group B sense wire for a short to B+ and check connector pin fit at both ends.
5. If charging voltage is normal and the wiring is intact, test the group B sense circuit and its connections for intermittent high readings while moving the harness.

Common fixes

• Repair a sense wire shorted to B+ or damaged insulation near a power feed.
• Clean and secure corroded or loose group B connector pins.
• Repair the charging system if its output exceeds the manufacturer's specification.
• Replace a failed sensing component only after the charging system and circuit wiring test correctly.

Can I keep driving?

If the engine runs smoothly and the warning light is steady, keep trips short and avoid heavy acceleration while the high reading is checked. Stop if there is a misfire, fuel smell, smoke or a flashing warning light, since continued driving can damage the catalytic converter.