P0295 – Cylinder 12 Injector Circuit High

P0295 is an OBD-II trouble code that points to a problem with one specific cylinder in your engine’s fuel and air control system: cylinder 12. You’ll usually see this code on larger engines, especially V12 or some heavy-duty applications. When the powertrain control module (PCM/ECU) detects that cylinder 12 isn’t responding as expected, it sets P0295 and may drop the engine into a reduced-power mode. If you’re noticing rough running, loss of power, or a check engine light, this guide will walk you through what P0295 means, why it happens, and how you can fix it.

What Does P0295 Mean?

P0295 is defined as “Cylinder 12 Injector Circuit High” or “Cylinder 12 Contribution/Balance Fault,” depending on the manufacturer. In plain language, the ECU sees an electrical or performance issue specific to cylinder 12, usually related to the fuel injector circuit or how that cylinder is contributing to overall engine power.

On most vehicles that can even have a cylinder 12, this code means the injector for that cylinder is drawing the wrong amount of current, has an open circuit, short to voltage, or the cylinder isn’t producing the expected power. The ECU compares crankshaft speed changes and injector feedback to flag the problem.

Quick Reference

• Code: P0295
• Meaning: Cylinder 12 injector circuit high / contribution fault
• Common Symptoms: Rough running, low power, misfire feel, check engine light
• Risk Level: Moderate to high if driven long-term
• Typical Fixes: Injector replacement, wiring repair, connector cleaning, ECU testing

Real-World Example / Field Notes

In the shop, I usually see P0295 on high-end V12 cars or heavy-duty trucks with multi-cylinder diesel engines. A common scenario: the owner complains of a subtle shake at idle and poor acceleration, but no obvious misfire code. Scan shows P0295 only. A quick injector balance test and a wiggle test on the harness often reveal a corroded connector or a broken wire near the injector plug. Once the connector is cleaned and the terminal tension restored, the code stays gone and the engine smooths right out.

Symptoms of P0295

• Check engine light on: The MIL/SES light will usually illuminate and store P0295 as a current or pending code.
• Rough idle: You may feel a subtle to noticeable vibration at idle from the missing or weak contribution of cylinder 12.
• Loss of power: Acceleration can feel flat or sluggish, especially under load or at higher RPM.
• Engine hesitation: You might notice a stumble or hesitation when you first step on the throttle.
• Increased fuel consumption: The ECU may compensate by enriching the mixture, leading to worse MPG.
• Exhaust odor or smoke: On diesels, you may see light white or gray smoke if that cylinder’s fueling is off.
• Possible limp mode: Some vehicles reduce power to protect the engine and emissions system.

Common Causes of P0295

Most Common Causes

• Faulty injector on cylinder 12: Internal electrical failure, coil open, or shorted windings can cause high circuit readings or poor fuel delivery.
• Damaged injector wiring harness: Chafed, pinched, or broken wires between the ECU and injector 12 are extremely common, especially near the valve cover or rail.
• Corroded or loose injector connector: Moisture, oil, and vibration can loosen terminals or cause green corrosion, raising resistance and confusing the ECU.
• Poor terminal tension: Spread terminals inside the connector can cause intermittent high resistance and random P0295 occurrences.
• ECU driver issue (less common but real): The injector driver circuit inside the ECU can fail and over- or under-supply voltage to that one injector.

Less Common Causes

• Low fuel pressure or rail issues: While this usually affects multiple cylinders, some systems will flag a specific cylinder if the imbalance is most noticeable there.
• Mechanical problem in cylinder 12: Low compression, valve issues, or a damaged piston can cause contribution faults that get coded as P0295.
• Aftermarket tuning or injector upgrades: Incorrect injector size or poor-quality tuning can throw off cylinder balance calculations.
• Ground or power supply problems: Shared grounds or power feeds to the injector bank can cause one cylinder to show up as the “weak link.”
• Water intrusion in harness: On some trucks and SUVs, water wicks into the loom and raises resistance right at the end of the circuit.

Diagnosis: Step-by-Step Guide

You’ll want a decent scan tool (preferably one that can read live data and Mode $06), a digital multimeter, basic hand tools, and ideally a noid light or injector test light. For diesels, an injector balance or contribution test function on your scan tool is very helpful.

1. Confirm the code and freeze-frame data. Connect your scan tool, read P0295, and note engine speed, load, and temperature when it set. Clear the code and see if it returns immediately or only under certain conditions.
2. Check for related codes. Look for misfire codes, other injector circuit codes, or fuel pressure codes. Multiple injector codes often point to a shared wiring or power issue.
3. Perform a visual inspection. Locate injector 12 (consult a service manual for bank and cylinder numbering). Inspect the connector, wiring loom, and nearby components for rubbing, oil saturation, broken clips, or melted insulation.
4. Wiggle test the harness. With the engine idling, gently move the harness and connector for injector 12 while watching live data or listening for a change in engine sound. If the idle stumbles or the code sets, you likely have an intermittent wiring fault.
5. Check injector resistance. With the key off and connector unplugged, measure resistance across the injector terminals using a multimeter. Compare to spec and to other injectors. A significantly higher or infinite reading indicates a bad injector.
6. Verify power and ground at the connector. With the key on, back-probe the injector connector. Confirm that you have proper voltage and a good ground or ECU control signal, depending on system design. A noid light can help verify pulse.
7. Swap components if possible. On some engines, you can swap injector 12 with another cylinder. If the code follows the injector (for example, becomes P0293 for cylinder 11), the injector is faulty. If it stays on cylinder 12, suspect wiring or ECU.
8. Run an injector balance or contribution test. Many scan tools can disable injectors one at a time or measure contribution. Cylinder 12 will show a different value or less RPM drop if it’s not working correctly.
9. Check ECU outputs and continuity. If wiring and injector test good, perform a continuity test from the injector connector back to the ECU pins. Look for high resistance or open circuits. If wiring is solid, the ECU driver may be failing.

Pro tip: Always inspect the entire length of the injector harness, not just at the connector. I’ve fixed many P0295 cases by repairing a hidden break where the loom bends around a bracket or rubs on the intake manifold.

Possible Fixes & Repair Costs

Repairs for P0295 depend on whether the issue is the injector, wiring, or ECU. A new or remanufactured injector for cylinder 12 typically runs $150–$600 for parts, plus 1–4 hours labor depending on engine access. Wiring repairs can range from a simple connector clean and re-pin (around $100–$250) to more extensive harness work ($300–$800). If the ECU injector driver is bad, replacement or repair can run $500–$1,500 or more. Costs vary by vehicle make, engine type (gas vs. diesel), and how buried that rear cylinder bank is.

Can I Still Drive With P0295?

You can usually drive short distances with P0295, but it’s not ideal. If the engine is only slightly rough and there’s no severe misfire, you might limp it to a shop. However, driving long-term with a dead or weak cylinder can increase stress on the rest of the engine, foul spark plugs (on gas engines), overload the catalytic converter or DPF, and cause poor fuel economy. If the engine is shaking badly, smoking, or going into limp mode, park it and have it towed to avoid further damage.

What Happens If You Ignore P0295?

Ignoring P0295 can turn a relatively simple injector or wiring repair into a much bigger problem. A cylinder that’s not fueling correctly can wash down cylinder walls, dilute engine oil, overheat the catalytic converter or DPF, and lead to internal engine wear. Over time, you risk costly damage like burned valves, piston issues, or emissions system failure, plus the constant risk of breakdown.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0295

P0295 is most often seen on vehicles with large multi-cylinder engines, especially V12 gasoline and diesel setups. You’ll find it on some Mercedes-Benz and BMW V12 luxury sedans and coupes, as well as certain high-end sports cars. In the diesel world, it can appear on heavy-duty trucks and commercial vehicles from manufacturers like Ford, GM, and various European brands that use multi-cylinder diesel engines. Because cylinder 12 is involved, you generally won’t see this code on typical 4-, 6-, or 8-cylinder daily drivers.