What it means
The control module detected a high electrical signal in the cylinder 1 injector B circuit. This indicates an electrical circuit condition; it does not by itself establish injector flow or cylinder fuel balance.
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 signal on the cylinder 1 injector B circuit. It sets P21DC when that signal is higher than expected, which can result from a short to voltage or a connector fault; the code concerns the circuit signal and does not confirm injector delivery.
Common causes
Most likely first.
- Short to voltage in wiring
- Damaged or corroded 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 data and check for cylinder 1 misfire or injector faults to identify when the high signal is present.
- Locate cylinder 1 injector B using service information and inspect the connector and harness for damaged insulation, corrosion, loose terminals, or contact with a powered wire.
- With ignition off, inspect the cylinder 1 injector B connector for bent or displaced terminals and check the nearby loom for signs of shorting.
- Using the manufacturer's test procedure, measure the cylinder 1 injector B circuit and check for a short to voltage or other cause of an above-expected signal.
- If the wiring and connector are intact, test injector B on cylinder 1 electrically for an internal fault.
Common fixes
- Clean and secure the cylinder 1 injector B connector or repair damaged terminals.
- Repair wiring that is shorted to voltage in the cylinder 1 injector B circuit.
- Replace cylinder 1 injector B if it fails the manufacturer's electrical test.
Can I keep driving?
With a steady light and smooth running, keep driving limited and gentle while arranging diagnosis; the cylinder 1 circuit fault can affect fueling and emissions. Stop if the light flashes, the engine misfires severely, or power falls sharply.
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.