P021A: Cylinder 7 Injection Timing

P021A reports a fault in the injection timing of cylinder 7 on a diesel engine. Unlike P01D7/P01D8 ('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. GM uses it as an electrical check on the 6.6 litre L5P Duramax V8: at every injection the engine module measures how long the injector current takes to reach its pull-in level of 13 A. If on the V8 that time is outside 60–150 µs in 10 of 20 samples, the code sets and the warning light comes on in the first trip. For 2020–2021 Silverado/Sierra HD, GM issued a software update against false setting. FCA's V6 and Ford do not use it.

Cylinder 7 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 7 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 P021A means

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

Frequently asked questions

Can I keep driving with code P021A?

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 P021A?

The most common causes are: injector of cylinder 7 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

• P01D7Cylinder 7 Injection Timing Performance - Over Retarded
• P01D8Cylinder 7 Injection Timing Performance - Over Advanced
• P0207Cylinder 7 Injector A Circuit/Open
• P02D8Cylinder 7 Fuel Injector A Offset Learning At Min Limit
• P0307Cylinder 7 Misfire Detected

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• static.nhtsa.gov: MC 10225608 0001

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.