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 the computer in your car has found a problem with the injector for the ninth cylinder. It's like when a light switch is stuck and can't turn off.
The code indicates that the electrical circuit controlling the injector for cylinder 9 is experiencing a higher voltage than expected.
P31A7 is set when the Engine Control Module (ECM) detects an abnormally high voltage in the low side circuit of the hydrogen injector for cylinder 9. This could indicate a short to voltage or an open circuit.
• Check Engine Light illuminated
• Engine misfire
• Reduced engine performance
• Faulty injector
• Wiring issues such as a short to voltage
• Faulty ECM
ECM: Engine Control Module
Injector: A device that introduces fuel into the engine's combustion chamber.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for cylinder 9 injector.
• Test the injector for proper operation.
• Repair or replace damaged wiring.
• Replace the faulty injector.
• Reprogram or replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 to $500
Moderate
• Toyota Mirai
• Hyundai Nexo
• Honda Clarity Fuel Cell
• Regularly inspect injector wiring.
• Ensure proper maintenance of fuel system.
• Use high-quality fuel.
Engine Performance
• Avoid driving the vehicle until repaired.
• Consult with a certified technician.
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code is more common in vehicles using alternative fuel systems, such as hydrogen fuel cells.
High – This issue can lead to engine performance problems and should be addressed promptly.
Driving with this code can lead to increased emissions and may not comply with local emissions regulations.
• Engine running
• Vehicle at operating temperature
The injector for cylinder 9 is located near the engine block, typically on the side of the engine where the cylinders are arranged.
Q: Can I drive with a P31A7 code?
A: It's not recommended to drive with this code as it can lead to engine performance issues.
Q: What happens if I ignore this code?
A: Ignoring this code can lead to further engine damage and increased emissions.
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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.