P21E3: Cylinder 4 Injector B Circuit High

P21E3 marks a high circuit state on the cylinder 4 B injector, normally a short to a supply line. On Mitsubishi's 2022 Eclipse Cross, where B is the direct high-pressure injector, the fault must persist 2 s; it closes the manual's list of direct injector circuit codes for the four cylinders. Because the direct injector driver uses boosted voltage, Mitsubishi tells technicians not to probe the terminals with a voltmeter and to work with resistance and continuity checks instead. GM's 2019 LT5 V8 assigns the same code to the supplemental injector of cylinder 4, stored as Type A when the low side sits within 0.5 Ohm of power with the driver off. The low counterpart is P21E2, the port injector high code on Mitsubishi P0271; from P21E4 on, the series continues with cylinder 5.

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

Symptoms

Check engine light on
Misfire on cylinder 4 (P0304)
Engine runs with reduced torque if further cylinders are affected

Most likely causes

Cylinder 4 injector line shorted to a supply wire
Injector of cylinder 4 shorted internally
Driver stage in the ECM or injection module damaged

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 can trigger limp mode.
It affects emissions.

What each character of P21E3 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
1: Air and fuel
E3: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21E3?

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 P21E3?

The most common causes are: cylinder 4 injector line shorted to a supply wire; injector of cylinder 4 shorted internally; driver stage in the ECM or injection module damaged.

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.