P021C reports a fault in the injection timing of cylinder 9 on a diesel engine. Unlike P01DB/P01DC ('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 9 code only applies to engines with 9 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.
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 9 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 9 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.
Good to know
- Repair difficulty: hard
- It affects emissions.
What each character of P021C means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 2: Fuel injection
- 1C: Specific fault in that system
Frequently asked questions
Can I keep driving with code P021C?
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 P021C?
The most common causes are: injector of cylinder 9 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
- P01DBCylinder 9 Injection Timing Performance - Over Retarded
- P01DCCylinder 9 Injection Timing Performance - Over Advanced
- P0209Cylinder 9 Injector A Circuit/Open
- P02DCCylinder 9 Fuel Injector A Offset Learning At Min Limit
- P0309Cylinder 9 Misfire Detected
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.