P2C27: Fuel Injector Group B Supply Sense Circuit Low

What it means

Voltage on the supply sense circuit of fuel injector group B is below the expected window. Indicates collapsed supply or short to ground.

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 injectors in group B receive power through a shared supply, and the ECM monitors a sense circuit for that feed. P2C27 sets when the sensed voltage falls below the expected range, consistent with a supply that sags or a sense wire pulled toward ground.

Common causes

Most likely first.

1. Supply rail collapsed under load
2. Sense wire shorted to ground
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. Read freeze-frame data and live group B supply-sense voltage, noting whether the low reading occurs at idle or under load.
2. Inspect the group B supply fuse, injector connectors and sense-wire routing for corrosion, loose pins, chafing or contact with ground.
3. Check for voltage at the group B supply feed under the conditions specified by the manufacturer and compare it with the manufacturer's specification.
4. With power off as directed by the manufacturer, check the sense wire for a short to ground and inspect connector pin fit at the ECM and group B branch.
5. If the wiring is intact, test the shared supply under load and isolate a collapsed feed or high-resistance connector by measuring voltage drop across connections.

Common fixes

• Clean and secure corroded group B connector pins and supply terminals.
• Repair a sense wire shorted to ground or damaged group B supply wiring.
• Replace a fuse or connector terminal that causes excessive voltage drop.
• Repair the shared supply feed if it collapses under load.

Can I keep driving?

Avoid hard acceleration and long trips if group B is misfiring; unburned fuel can overheat the catalytic converter. Stop driving if the engine runs very roughly, fuel smell or exhaust smoke appears, or the warning light flashes.