P21ED: Cylinder 9 Injector B Circuit High

P21ED is defined for a B injector circuit on cylinder 9 that reads high, meaning the control side is shorted to supply or, on some designs, the two injector wires touch. No manufacturer publishes thresholds or vehicles for it. Only engines with ten or more cylinders and dual injection could set it; Lamborghini's Huracán V10 with direct plus multi-point injection is the documented example, although its A/B naming is not public. CARB requires that an output component be flagged when it does not respond properly to commands, which is exactly the case here: the injector cannot be switched, so cylinder 9 depends on its other injector alone. Lean running at loads where both injectors work together is the likely result. Low fault: P21EC; A injector high fault: P0286.

Medium severity. Can I keep driving?Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

Cylinder 9 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

Check engine light on
Cylinder 9 lean in mixed injection operation
Misfire on cylinder 9 (P0309)

Most likely causes

Control wire of the cylinder 9 B injector shorted to power
Both injector wires bridged in the harness
Injector coil shorted internally
Driver stage in the control unit faulty

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring of the injector indicated
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Measure the resistance and compare it with the manufacturer's specification
Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
On diesels, check the per-cylinder injection corrections

Good to know

Repair difficulty: hard
It affects emissions.

What each character of P21ED means

P: Powertrain: engine and transmission
2: Generic code: same on every make
1: Air and fuel
ED: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21ED?

Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

What causes code P21ED?

The most common causes are: control wire of the cylinder 9 B injector shorted to power; both injector wires bridged in the harness; injector coil shorted internally.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.