Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means the car's computer has detected a problem with the fuel injector for cylinder 4. It's like a small pipe that sprays fuel into the engine, and it's not working properly.
The P318B code indicates an issue with the electrical circuit that controls the low side of the fuel injector for cylinder 4. This can affect how the engine runs.
The P318B code is triggered when the Engine Control Module (ECM) detects a low voltage condition in the low side circuit of the hydrogen injector for cylinder 4. This can be due to a wiring issue, a faulty injector, or a problem with the ECM itself.
• Engine misfire
• Reduced engine performance
• Check Engine Light illuminated
• Faulty fuel injector
• Damaged wiring or connectors
• Malfunctioning Engine Control Module (ECM)
ECM: Engine Control Module, the computer that controls engine functions.
Injector: A device that sprays fuel into the engine's cylinders.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for cylinder 4 injector.
• Test the injector for proper operation.
• Replace the faulty injector.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $500
Moderate
• Toyota Mirai
• Honda Clarity Fuel Cell
• Hyundai Nexo
• Regular maintenance checks
• Inspect wiring for wear and tear
• Use high-quality fuel
Engine Performance
• Do not ignore the Check Engine Light.
• Consult a professional mechanic for diagnosis.
• Avoid driving the vehicle if performance issues are severe.
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code is relatively rare and specific to vehicles using hydrogen fuel injection systems.
Moderate – Address the issue soon to prevent further engine performance problems.
Driving with a malfunctioning injector can lead to increased emissions and potential engine damage.
• Engine at operating temperature
• Vehicle in a safe, stationary position
The injector for cylinder 4 is located on the engine block, typically on the side where the fuel rail is mounted.
Q: Can I drive with a P318B code?
A: It's not recommended to drive for long periods with this code, as it can cause engine performance issues.
Q: How do I reset the Check Engine Light?
A: After repairs, use an OBD-II scanner to clear the code. If the issue is fixed, the light should stay off.
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Universal · Digital multimeter
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Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
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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.