Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This means there's a problem with the part of the engine that helps inject fuel into cylinder number 5. It's like when a wire that should be separate is touching something it shouldn't, causing a problem.
The code indicates that the high side of the hydrogen injector circuit for cylinder 5 is shorted to the ignition coil circuit.
The P31B5 code is triggered when the engine control module (ECM) detects that the high side of the hydrogen injector circuit for cylinder 5 is shorted to the ignition coil circuit. This can affect the injector's ability to function properly, leading to engine performance issues.
• Engine misfire
• Reduced engine performance
• Check Engine Light illuminated
• Damaged wiring harness
• Faulty hydrogen injector
• Short circuit in the ignition coil
ECM: Engine Control Module
Injector: A device that introduces fuel into the engine's combustion chamber
• Inspect the wiring harness for damage or corrosion.
• Check the hydrogen injector for proper operation.
• Test the ignition coil circuit for shorts.
• Repair or replace damaged wiring.
• Replace the faulty hydrogen injector.
• Repair the ignition coil circuit.
• Multimeter
• OBD-II scanner
• Wiring diagram
$150 - $500
Moderate
• Toyota Mirai
• Hyundai Nexo
• Honda Clarity Fuel Cell
• Regularly inspect wiring for damage.
• Ensure proper maintenance of fuel system components.
• Avoid harsh driving conditions that can stress engine components.
Engine Performance
• Have the vehicle inspected by a professional.
• Avoid driving the vehicle until the issue is resolved to prevent further damage.
Check with the vehicle manufacturer for warranty coverage on fuel system components.
This code is relatively rare and is specific to vehicles using hydrogen fuel injection systems.
High – This issue can lead to engine performance problems and should be addressed promptly.
Driving with this issue may not comply with emissions regulations and can be unsafe.
• Engine running
• OBD-II scanner connected
The hydrogen injector for cylinder 5 is located on the engine, near the intake manifold.
Q: Can I drive my car with a P31B5 code?
A: It's not recommended to drive with this code as it can lead to further engine damage.
Q: What causes a hydrogen injector to short?
A: Common causes include damaged wiring or a faulty injector.
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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.