P21D0: Cylinder 2 Injector B Circuit/Open

P21D0 is the open-circuit code for the B injector of cylinder 2. Where that cylinder sits varies: GM's small-block V8 alternates odd and even numbers between the banks, so cylinder 2 opens the right bank, while Ford's V6 and V8 count one bank first and place it next to cylinder 1. Ford defines B as the port injector, the direct injector being A with P0202. Ford runs the check in every engine with combined port and direct injection, from the three-cylinder 1.5 to the 5.0 V8, continuously at 11 V or more for 5 s. GM's LT5 injection module samples the circuit every 100 ms once the powertrain relay supplies at least 11 V. On engines that run on port fuel alone at light load, like Ford's second 3.5 EcoBoost, the cylinder then misfires mostly at idle. Low and high faults are P21DE and P21DF.

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

Symptoms

Check engine light on
Misfire on cylinder 2, mainly at idle and light load
Code P0302 stored as well

Most likely causes

Port injector of cylinder 2 with an open winding
Broken wire or pushed-back terminal in the injector harness
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 P21D0 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
1: Air and fuel
D0: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21D0?

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 P21D0?

The most common causes are: port injector of cylinder 2 with an open winding; broken wire or pushed-back terminal in the injector harness; 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.