P28C2: Ion Sense Module Supply Voltage High

What it means

Supply voltage on the ion sense module is above the expected window. Charging system overvoltage or upstream regulator fault.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The ion-sense module's supply powers the circuit that biases the spark plug for ion-current measurement. This code sets when the engine control module detects supply voltage above the expected range, which can result from charging-system overvoltage or a supply wire shorted to battery voltage.

Common causes

Most likely first.

1. Alternator regulator drift - overvoltage
2. Supply wire shorted to B+

Symptoms

• Check-engine light
• Reduced power
• Hard starting or stalling

How to diagnose it

1. Review freeze-frame and charging-system data, along with related voltage codes, to see whether the high reading coincided with an overvoltage event.
2. Inspect the module supply wiring and connector for damage or contact with a battery-voltage wire.
3. Measure charging-system voltage under the conditions specified by the manufacturer and compare it with the manufacturer's specification.
4. Check the ion-sense module supply for a short to battery voltage, using the wiring diagram and the manufacturer's test procedure.
5. If charging voltage and wiring are correct, test the upstream supply control and module as directed by the manufacturer.

Common fixes

• Repair a module supply wire shorted to battery voltage.
• Clean or repair damaged or corroded supply connector terminals.
• Repair or replace a confirmed faulty charging-system regulator.
• Replace the ion-sense module only if its supply is within specification and testing confirms an internal fault.

Can I keep driving?

Avoid extended driving until the charging system's voltage is checked, especially if other electrical warnings or symptoms appear. Overvoltage can affect other vehicle electronics as well as the ion-sense system.