P21EB: Cylinder 8 Injector B Circuit High

What it means

The control module detected a high electrical signal in the cylinder 8 injector B circuit. This indicates an electrical circuit condition; it does not by itself establish injector flow or cylinder fuel balance.

At a glance

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

How it works

Cylinder 8 injector B is the injector identified for cylinder 8, and its driver circuit carries the electrical command that operates it. The control module monitors the circuit response and sets P21EB when the signal is higher than expected. This is an electrical circuit condition, often involving a short to voltage, and does not confirm injector flow.

Common causes

Most likely first.

1. Short to voltage in wiring
2. Damaged or corroded connector
3. Injector electrical fault

Symptoms

• Check-engine light on
• Rough running or misfire
• Reduced engine power
• Increased fuel consumption

How to diagnose it

1. Save freeze-frame data and check live misfire counts and fuel trims to establish when the cylinder 8 injector B circuit fault appears and whether cylinder 8 is misfiring.
2. With the engine off, inspect the cylinder 8 injector B connector and nearby harness for corrosion, loose pins, chafing, heat damage, or contact with a power source.
3. Use the wiring diagram to test the cylinder 8 injector B circuit for a short to voltage, an open, or a poor connection to the control module.
4. Isolate the circuit according to the manufacturer's procedure and test the injector’s electrical condition against the manufacturer's specification; check whether the high signal remains when it is disconnected.
5. If the wiring and injector pass, test the cylinder 8 injector B driver circuit at the control module using the manufacturer's diagnostic procedure.

Common fixes

• Clean and secure a corroded or loose cylinder 8 injector B connector.
• Repair wiring shorted to voltage or damaged in the cylinder 8 injector B circuit.
• Replace cylinder 8 injector B if its electrical test is outside the manufacturer's specification.
• Repair or replace the control module only if its cylinder 8 injector B driver fails the specified tests.

Can I keep driving?

If the engine runs normally and the warning light is steady, limit driving and avoid high loads until the fault is diagnosed. Stop if the light flashes, the engine misfires badly, or power drops substantially, since a sustained misfire can damage the catalytic converter.