P021B code meaning
Cylinder 8 Injection Timing
Powertrain system Generic code P02xx codes Check engine light
What P021B means
P021B reports a fault in the injection timing of cylinder 8 on a diesel engine. Unlike P01D9/P01DA ('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.
P021B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P021B
- Check engine light on
- Rough running or misfire, rough idle
- Loss of power, smoke or knocking possible
Common causes of P021B
- Most likelyInjector of cylinder 8 faulty (coil, armature, wear, deposits)
- PossibleInjector wiring or connector: contact resistance, corrosion, chafing
- PossibleEngine software sets the code falsely (update available for some models)
- Less likelyInjector driver stage or boost voltage in the engine module
- Less likelyWrong injector code, contaminated fuel or loose injector clamp
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel injector cylinder 8Injector wiringEngine control module
What each part of P021B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 2 | Area: fuel and air metering (injector circuit). |
| 1B | The exact fault in that area. |
What to do next
- Note P021B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P021B
What does P021B mean?
P021B means "Cylinder 8 Injection Timing". P021B reports a fault in the injection timing of cylinder 8 on a diesel engine. It is a generic code, so it means the same on every make.
Is it safe to drive with P021B?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P021B fail an emissions test?
Yes, it can. P021B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P021B to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P021B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.