P21E9: Cylinder 7 Injector B Circuit High

What it means

The control module detected a high electrical signal in the cylinder 7 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 7 injector B is the injector identified for cylinder 7, and its driver circuit carries the electrical command that operates it. The control module monitors the circuit response and sets P21E9 when the signal is higher than expected. This indicates an electrical issue such as a short to voltage; it does not by itself show whether the injector is flowing correctly.

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 review live misfire counts and fuel trims to identify when the cylinder 7 injector B circuit fault occurs and whether cylinder 7 is misfiring.
2. With the engine off, inspect the cylinder 7 injector B connector and nearby wiring for corrosion, loose pins, melted insulation, chafing, or contact with a power feed.
3. Follow the wiring diagram to check the cylinder 7 injector B circuit for a short to voltage, an open, or a poor connection between the injector and control module.
4. Isolate the circuit as specified by the manufacturer and test the injector’s electrical condition against the manufacturer's specification, noting whether the high signal persists with it disconnected.
5. If the wiring and injector test correctly, check the cylinder 7 injector B driver output at the control module using the manufacturer's procedure.

Common fixes

• Clean and secure a corroded or loose cylinder 7 injector B connector.
• Repair wiring shorted to voltage or damaged in the cylinder 7 injector B circuit.
• Replace cylinder 7 injector B if its electrical test is outside the manufacturer's specification.
• Repair or replace the control module only if its cylinder 7 injector B driver fails the specified tests.

Can I keep driving?

If the engine runs normally and the warning light stays steady, drive only as needed and avoid hard acceleration until the fault is addressed. Stop if the light flashes or the engine misfires heavily, as continued misfire can overheat and damage the catalytic converter.