P21D3: Cylinder 5 Injector B Circuit/Open

P21D3 can only appear on engines with at least five cylinders and two injectors per cylinder. Documented users are Ford's dual-injection V6 and V8 engines (2.7 and 3.5 EcoBoost of the second generation, 5.0 V8 from 2018) and GM's supercharged LT5 V8. Ford defines B as the port injector; the direct injector of this cylinder is A, coded P0205. GM stores it as Type A once 20 of 25 samples fail. Ford's check is continuous above 11 V with a 5 s window. GM's LT5 injection module rates an open by the impedance seen with the driver off, 200 kOhm or more. On a V6 one bank then runs with a single weak cylinder, which fuel trims and misfire counters can reveal.

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

Symptoms

Check engine light on
Misfire on cylinder 5 (P0305)
Fuel trim of one bank shifted

Most likely causes

Open coil in the cylinder 5 port injector
Broken wire in the bank harness of the port injectors
Output stage in the engine or injection module failed

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 continuity of the wire between the component and the control module.
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: medium
It affects emissions.

What each character of P21D3 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
1: Air and fuel
D3: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21D3?

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 P21D3?

The most common causes are: open coil in the cylinder 5 port injector; broken wire in the bank harness of the port injectors; output stage in the engine or injection module failed.

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.