P21DE: Cylinder 2 Injector B Circuit Low

What it means

The control module detected a low electrical signal in the cylinder 2 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

Injector B is the second injector circuit identified for cylinder 2 by the control system; the code does not establish whether the injector is delivering the right amount of fuel. The control module sets P21DE when it detects a low electrical signal in that circuit, commonly from a short to ground, a poor connection, or an injector electrical fault.

Common causes

Most likely first.

1. Short to ground in wiring
2. Damaged or corroded connector
3. Injector electrical fault

Symptoms

• Check-engine light on
• Rough running or misfire
• Reduced engine power
• Increased fuel consumption

How to diagnose it

1. Save freeze-frame data, then check for cylinder 2 misfire and related injector codes to see whether the fault coincides with rough running or load.
2. Inspect the cylinder 2 injector B connector and nearby harness for corrosion, loose pins, chafing, or wires pinched against the engine.
3. Use the vehicle’s wiring information to identify injector B’s cylinder 2 circuit and check for an unintended short to ground.
4. Check the connector terminals and circuit continuity with the injector disconnected, following the manufacturer’s isolation procedure.
5. Test injector B’s electrical condition against the manufacturer’s specification and compare with other injectors only where the system design permits.

Common fixes

• Reconnect and secure the cylinder 2 injector B connector; clean corrosion if present.
• Repair chafed or shorted-to-ground wiring in the cylinder 2 injector B circuit.
• Replace a damaged connector or terminal that cannot maintain a sound connection.
• Replace injector B for cylinder 2 if its electrical test confirms an internal fault.

Can I keep driving?

If the engine runs roughly or loses power, avoid hard acceleration and long trips; an injector circuit fault can worsen misfiring and emissions and may damage the catalytic converter. Stop driving if the engine runs severely unevenly or the warning light flashes.