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 electrical circuit that controls the fuel injector for cylinder 5 in your car's engine. It's like a light switch not working properly to turn on a light.
The code indicates an issue with the high side circuit of the high-pressure injector for cylinder 5, suggesting that the circuit is not getting enough voltage or is grounded.
The P31C8 code is triggered when the Engine Control Module (ECM) detects a low voltage condition in the high side circuit of the high-pressure fuel injector for cylinder 5. This could be due to a short to ground, an open circuit, or a faulty injector.
• Engine misfire
• Rough idling
• Decreased fuel efficiency
• Faulty fuel injector
• Open or shorted injector circuit
• Poor electrical connection in the injector circuit
ECM: Engine Control Module
OBD-II: On-Board Diagnostics II
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for cylinder 5 injector.
• Test the injector for proper resistance and operation.
• Repair or replace damaged wiring or connectors.
• Replace the faulty fuel injector.
• Clear the code and test drive to ensure the issue is resolved.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $400
Moderate
• BMW 3 Series
• Audi A4
• Mercedes-Benz C-Class
• Regularly inspect and maintain the fuel injector system.
• Use high-quality fuel to prevent injector clogging.
• Perform regular engine diagnostics.
Engine Performance
• Avoid driving with a misfiring engine to prevent further damage.
• Schedule a diagnostic check with a professional mechanic.
Check your vehicle's warranty for coverage on fuel injector issues.
This code is commonly associated with high-mileage vehicles or those with known injector issues.
Moderate – Addressing this issue promptly can prevent further engine damage.
Ignoring this code may lead to increased emissions and potential engine damage.
• Engine at operating temperature
• Under load conditions
The fuel injector for cylinder 5 is located on the engine block, typically accessible from the top of the engine.
Q: Can I drive my car with this code?
A: It's not recommended, as driving with a misfiring engine can cause further damage.
Q: How can I prevent this issue?
A: Regular maintenance and using quality fuel can help prevent injector issues.
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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.