P21A4

Cylinder 9 Air-Fuel Ratio Imbalance

Severity

⚠️ Medium

Can you drive?

Yes, but get it checked soon

Approx. repair cost

$17–89 (est.)

Symptoms

Uneven engine operation
Increased fuel consumption
Reduced engine power
Check Engine Light Illuminates
Possible misfire in cylinder 9

Causes

Malfunction of the fuel injector of cylinder 9
Problems with the spark plug or coil in cylinder 9
Vacuum leaks in the area of cylinder 9
Dirty or faulty oxygen sensor
Compression problems in cylinder 9

How to Fix

Check the condition of the spark plug and coil in cylinder 9
Test the performance of the cylinder 9 fuel injector
Check the tightness of the intake tract at cylinder 9
Check the oxygen sensor readings
Measure compression in cylinder 9

Related codes

P21A0 P21A1 P21A2 P21A3