Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that something is wrong with the electrical connection to the fuel injector for cylinder number 6 in the engine. It's like a broken wire or a loose plug that stops the injector from working properly.
The code indicates an issue with the electrical circuit that controls the fuel injector for cylinder 6. This could be due to an open circuit, meaning there is a break in the wiring or a poor connection.
P21D4 is triggered when the Engine Control Module (ECM) detects an open circuit or a fault in the electrical circuit of the injector B for cylinder 6. This could be due to a broken wire, a faulty injector, or a poor connection in the circuit.
• Engine misfire
• Check Engine Light on
• Reduced engine performance
• Faulty fuel injector
• Broken or damaged wiring
• Poor electrical connection
ECM: Engine Control Module
OBD-II: On-Board Diagnostics, Second Generation
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for cylinder 6 injector.
• Test the fuel injector for proper operation.
• Repair or replace damaged wiring.
• Clean or reconnect electrical connectors.
• Replace the faulty fuel injector.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $400
Moderate
• Ford F-150
• Chevrolet Silverado
• Dodge Ram 1500
• Regularly inspect and maintain wiring harnesses.
• Use fuel system cleaners periodically.
• Ensure proper electrical connections.
Engine Performance
• Avoid driving with a misfiring engine as it can cause further damage.
• Have the issue diagnosed and repaired by a professional mechanic.
Check with your vehicle manufacturer for warranty coverage on fuel injectors.
This code has been associated with issues in vehicles with higher mileage where wiring harnesses may degrade over time.
Moderate – It should be addressed soon to avoid potential engine damage.
Driving with a misfiring engine can lead to increased emissions and may not comply with local emissions laws.
• Engine running
• Electrical system active
The fuel injector for cylinder 6 is located on the engine block, typically under the intake manifold.
Q: Can I drive my car with this code?
A: It's not recommended to drive for long distances as it can cause engine damage.
Q: How do I reset the check engine light?
A: After fixing the issue, you can reset the light using an OBD-II scanner.
High-End · Full-system diagnostics
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Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
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Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
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Fitment Required · Vehicle-fitment part
Commonly relevant for misfire, ignition-efficiency, and some drivability-related repairs.
Misfire and ignition-related faults commonly involve spark plugs as part of the repair path.
Check the correct plug type, gap, and engine application for your vehicle.
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Fitment Required · Vehicle-fitment part
Relevant when the fault points toward ignition-coil performance or cylinder-specific ignition issues.
Some ignition faults involve coil performance or cylinder-specific coil problems.
Match the coil to your engine and confirm the failed component before ordering.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.