P21D1: Cylinder 3 Injector B Circuit/Open

P21D1 concerns the B injector of cylinder 3, which on Ford's 1.5 EcoBoost three-cylinder is the last one in the block. That engine combines port and direct fuel, and Ford names the port injectors B. Bulletin SSM 49996 for the 2021 Bronco Sport describes P21CF, P21D0 and P21D1 appearing together with transmission and other codes, in some cases with a no-crank condition, because the harness was damaged at the transmission cover; when all three B codes show at once, a shared wiring fault is far more likely than three bad injectors. Ford's summary checks the B circuits continuously above 11 V within 5 s. GM's LT5 V8 module flags an open low side once 20 of 25 samples fail. The direct injector of the cylinder is coded P0203.

Cylinder 3 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

• Check engine light on
• Rough running or misfire on cylinder 3
• With harness damage also transmission codes or no crank

Most likely causes

• Harness damage affecting several injectors at once (Ford Bronco Sport, transmission cover)
• Open coil in the cylinder 3 port injector
• Connector not latched or corroded

What to check, in order

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

1. Check the connector and wiring of the injector indicated
2. Check the continuity of the wire between the component and the control module.
3. Measure the resistance and compare it with the manufacturer's specification
4. Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
5. On diesels, check the per-cylinder injection corrections

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P21D1 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 1: Air and fuel
• D1: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21D1?

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 P21D1?

The most common causes are: harness damage affecting several injectors at once (Ford Bronco Sport, transmission cover); open coil in the cylinder 3 port injector; connector not latched or corroded.

Related codes

• P0203Cylinder 3 Injector A Circuit/Open
• P21E0Cylinder 3 Injector B Circuit Low
• P21E1Cylinder 3 Injector B Circuit High
• P21CFCylinder 1 Injector B Circuit/Open
• P21D0Cylinder 2 Injector B Circuit/Open
• P0303Cylinder 3 Misfire Detected

Sources

• static.nhtsa.gov: MC 10200984 0001
• fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023
• en.wikipedia.org: Ford EcoBoost engine
• gsi.ext.gm.com: 19OBDG03A Diagnostics

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.