Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means there's a problem with the fuel injector in the car's engine. It's like a tiny hose that sprays fuel into the engine, and it's not working right because it's getting mixed up with another part's electricity.
The P31B2 code indicates that the high side of the hydrogen (H2) injector circuit for cylinder 2 is shorted to the coil circuit, causing improper operation.
The P31B2 code is triggered when the engine control module (ECM) detects a short circuit between the high side of the hydrogen injector for cylinder 2 and the ignition coil circuit. This can cause improper fuel delivery and affect engine performance.
• Engine misfire
• Poor fuel economy
• Check Engine Light is on
• Faulty H2 injector
• Damaged wiring or connectors
• Faulty ignition coil
ECM: Engine Control Module
Injector: A device that sprays fuel into the engine
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for damage.
• Test the H2 injector and ignition coil for proper operation.
• Replace the faulty H2 injector.
• Repair or replace damaged wiring or connectors.
• Replace the faulty ignition coil.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $500
Moderate
• Toyota Mirai
• Honda Clarity Fuel Cell
• Hyundai Nexo
• Regular maintenance checks
• Ensure wiring is intact and secure
• Use quality fuel
Engine Performance
• Do not ignore the Check Engine Light.
• Have the vehicle inspected by a professional if unsure.
Check with the vehicle manufacturer for warranty coverage on fuel injectors and ignition components.
This code is relatively rare and specific to vehicles using hydrogen fuel injection systems.
Moderate – Should be addressed soon to prevent further engine issues.
Driving with a malfunctioning injector can lead to increased emissions and potential engine damage.
• Engine running
• Electrical system active
The H2 injector for cylinder 2 is located on the engine, typically near the intake manifold.
Q: Can I drive with a P31B2 code?
A: It's not recommended to drive for long periods with this code, as it can lead to engine damage.
Q: How can I prevent this issue?
A: Regular maintenance and inspections can help prevent wiring issues that lead to this code.
High-End · Full-system diagnostics
A full-system bidirectional platform aimed at advanced DIY users and professional diagnostic workflows.
Network faults often require full-system access instead of a generic code reader alone.
View on Amazon
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.
View on Amazon
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.
View on AmazonThese are optional diagnostic tools, not guaranteed fixes. As an Amazon Associate I earn from qualifying purchases.
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.
View options on Amazon
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.