P021F: Cylinder 12 Injection Timing

P021F reports a fault in the injection timing of cylinder 12 on a diesel engine. Unlike P01E1/P01E2 ('over retarded/advanced', the result of the injector learning routine in overrun), this code has no direction, and what it checks is up to the manufacturer. A cylinder 12 code only applies to engines with 12 or more cylinders. No manufacturer or vehicle using it was found – GM's documents stop at cylinder 8 (P021B), FCA's at cylinder 6, and Ford uses other codes. The description therefore follows the documented siblings: GM checks the injector's current rise electrically, FCA ties the code to injector learning. CARB requires diesel engines to detect injection that is too early or too late.

Cylinder 12 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

• Check engine light on
• Rough running or misfire, rough idle
• Loss of power, smoke or knocking possible

Most likely causes

• Injector of cylinder 12 faulty (coil, armature, wear, deposits)
• Injector wiring or connector: contact resistance, corrosion, chafing
• Engine software sets the code falsely (update available for some models)
• Injector driver stage or boost voltage in the engine module
• Wrong injector code, contaminated fuel or loose injector clamp

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. Measure the resistance and compare it with the manufacturer's specification
3. Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
4. On diesels, check the per-cylinder injection corrections

Good to know

• Repair difficulty: hard
• It affects emissions.

What each character of P021F means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 2: Fuel injection
• 1F: Specific fault in that system

Frequently asked questions

Can I keep driving with code P021F?

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 P021F?

The most common causes are: injector of cylinder 12 faulty (coil, armature, wear, deposits); injector wiring or connector: contact resistance, corrosion, chafing; engine software sets the code falsely (update available for some models).

Related codes

• P01E1Cylinder 12 Injection Timing Performance - Over Retarded
• P01E2Cylinder 12 Injection Timing Performance - Over Advanced
• P0212Cylinder 12 Injector A Circuit/Open
• P232DCylinder 12 Fuel Injector A Offset Learning At Min Limit
• P0312Cylinder 12 Misfire Detected

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 18OBDG04 Engine 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.