What it means
The control module detected an open or otherwise faulty electrical circuit for cylinder 8 injector B. The code identifies the circuit fault; it does not establish what injector B refers to on a particular engine.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine control module monitors the electrical circuit that commands injector B for cylinder 8. P21D6 indicates that the circuit has been detected as open or otherwise electrically faulty, so cylinder 8 may not receive its requested fuel; the code does not specify the vehicle’s injector B arrangement.
Common causes
Most likely first.
- Open or damaged wiring
- Loose or corroded injector connector
- Injector electrical fault
Symptoms
- Check-engine light on
- Rough running or misfire
- Reduced engine power
- Increased fuel consumption
How to diagnose it
- Capture freeze-frame information and review related cylinder 8 misfire or injector codes to understand when the fault appears.
- Identify cylinder 8 and injector B using vehicle service information, then visually inspect its connector and harness for looseness, corrosion, cuts, or abrasion.
- With ignition off, examine the cylinder 8 injector B plug terminals for poor contact, contamination, or pins displaced in the housing.
- Check the injector B circuit for continuity and compare the result with the manufacturer's specification, including relevant harness sections.
- If the circuit is intact, electrically test the cylinder 8 injector B to check for an internal open or other failure.
Common fixes
- Reseat the cylinder 8 injector B connector and clean or repair its terminals.
- Repair an open or damaged wire in the cylinder 8 injector B circuit.
- Replace cylinder 8 injector B if its electrical test shows an internal fault.
Can I keep driving?
With a steady light and no noticeable roughness, drive only as needed and gently until the cylinder 8 circuit is diagnosed. Avoid towing or hard acceleration; stop if the light flashes, misfire becomes pronounced, or the engine loses substantial power.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.