What Does P021B Mean?
This code indicates cylinder 8 injection timing is outside the ECM's acceptable range. On direct injection or diesel engines with eight or more cylinders, the ECM monitors each cylinder's injection timing individually. Cylinder 8 is firing fuel at an incorrect point, affecting combustion efficiency.
Common Causes
35%
Cylinder 8 injector with worn internal components causing delayed or premature fuel delivery
25%
Carbon buildup on the cylinder 8 injector nozzle altering spray characteristics and timing
20%
Fuel rail pressure wave irregularity affecting the cylinder 8 injection event
20%
Engine position sensor or timing chain issue creating a timing calculation error
Diagnostic Steps
1
Step 1: Compare injection timing correction data across all cylinders on a scan tool to isolate cylinder 8.
2
Step 2: Perform an injector balance test for cylinder 8 and compare contribution to other cylinders.
3
Step 3: Swap cylinder 8 injector with another on the same bank to determine if the fault follows the injector.
4
Step 4: Inspect cylinder 8 injector tip for carbon deposits using a borescope.
5
Step 5: Check timing chain stretch and position sensor signals to rule out mechanical timing errors.
Estimated Repair Cost
$200 - $950
Parts + labor, varies by vehicle and location
This code indicates cylinder 8 injection timing is outside the ECM's acceptable range. On direct injection or diesel engines with eight or more cylinders, the ECM monitors each cylinder's injection timing individually. Cylinder 8 is firing fuel at an incorrect point, affecting combustion efficiency.
The most common cause of P021B (Cylinder 8 Injection Timing) is: Cylinder 8 injector with worn internal components causing delayed or premature fuel delivery
Typical repair costs for P021B range from $200 to $950, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Incorrect cylinder 8 injection timing increases emissions, combustion noise, and can cause piston damage on diesel engines if severely deviated.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P021B to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel Injection System / Engine Timing
Difficulty
Type
Generic (SAE)
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