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 there is an electrical problem with the injector for cylinder 1 in your car's engine. It's like a wire is touching something it shouldn't, causing a short circuit.
The P31B1 code indicates that the high side of the injector circuit for cylinder 1 is shorted to the ignition coil circuit, which can cause improper injector operation.
The P31B1 code is triggered when the Engine Control Module (ECM) detects a short circuit between the high side of the fuel injector for cylinder 1 and the ignition coil. This can lead to improper fuel delivery and engine misfires.
• Engine misfire
• Poor fuel economy
• Check engine light illuminated
• Damaged wiring harness
• Faulty fuel injector
• Short circuit in the ignition coil
ECM: Engine Control Module
Injector: A device that sprays fuel into the engine's cylinders
• Inspect the wiring harness for damage or wear.
• Check the injector and ignition coil connections.
• Use a multimeter to test for continuity and shorts in the circuit.
• Repair or replace damaged wiring.
• Replace the faulty fuel injector.
• Repair or replace the ignition coil if necessary.
• Multimeter
• OBD-II scanner
• Basic hand tools
$150 - $500
Moderate
• Toyota Camry
• Honda Accord
• Ford F-150
• Regularly inspect and maintain wiring harnesses.
• Ensure proper installation of fuel injectors.
• Avoid exposure to moisture and contaminants.
Engine Performance
• Do not ignore the check engine light.
• Have a professional diagnose the issue if unsure.
• Regular maintenance can prevent such issues.
Check with your vehicle manufacturer for warranty coverage on engine components.
This code has been associated with injector and ignition coil issues in various vehicle models over the years.
Moderate – Address the issue to avoid potential engine damage.
Ignoring this issue can lead to increased emissions and potential engine damage.
• Engine running
• Warm engine temperature
The fuel injector for cylinder 1 is located on the engine's intake manifold, near the first cylinder.
Q: Can I drive with a P31B1 code?
A: It's not recommended to drive for extended periods with this code, as it can cause engine damage.
Q: How can I prevent a P31B1 code?
A: Regular maintenance and inspections of the wiring and fuel system can help prevent this code.
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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.