P0294 code: Cylinder 12 Injector Circuit Low
P0294 means cylinder 12 Injector Circuit Low. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0294 means
P0294 covers the last injector on the largest common engine layout: it sets when the ECM measures below-expected voltage on the cylinder 12 injector control circuit, and only twelve-cylinder engines (V12 and W12 layouts) can generate it. The low-voltage fault pattern points to a short to ground in the wiring, an open circuit, or an injector coil that has shorted internally. Like the rest of this code family, it judges the electrical path exclusively — a clogged injector is a mechanical fuel restriction that leaves circuit voltage untouched and shows up as a misfire code instead. With eleven identical healthy circuits available for comparison, diagnosis is methodical: resistance-check cylinder 12's injector against a neighbor, inspect its connector, and swap-test if results are unclear. Companion codes are P0212 (cylinder 12 injector circuit) and P0312 (cylinder 12 misfire). Confirm cylinder 12's physical position from your engine's numbering diagram, as twelve-cylinder conventions differ across manufacturers.
P0294 symptoms
- Misfire on cylinder 12, typically well-masked by the other eleven
- Slight coarseness at idle or under load
- Minor power and refinement loss
- Check-engine light, flashing if the misfire is sustained
- Possibly no symptoms at all when the fault is intermittent
What it costs to fix P0294
Typical range: $60–$450 · about ~0.5–2 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Fuel injector (single) | $50–$300 | ~0.5–2 hrs |
| Wiring/connector repair | $5–$50 | ~0.5–2 hrs |
Cylinder 12 usually sits at the rear of a bank in a densely packed twelve-cylinder bay — access labor tends toward and beyond the top of the range, and direct-injection injectors for these engines are premium-priced. The wiring-repair outcome is far cheaper.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0294 for my exact vehicle →
How to fix P0294
Advanced — usually a shop job unless you’re well equipped
- Rule out a shared fault across the bank
Scan all engine modules first. If several injectors on cylinder 12's bank have circuit codes too, check what they have in common — the injector feed fuse or relay and any inline harness connector — before chasing anything specific to cylinder 12. A lone P0294 points at the cylinder 12 injector or its own wiring leg.
- Inspect the rear of the engine for heat damage
Cylinder 12 is often the rearmost cylinder on its bank, close to the firewall where heat collects and the harness is clipped tight against the body. Look for insulation that has hardened, cracked, or melted against an exhaust component, and for wires rubbed through where the engine moves against the bulkhead.
- Compare injector 12 with its neighbours on a meter
Unplug injector 12 and two others on the same bank and measure each across its terminals. Similar values clear the injector; a figure on 12 well below the others means internal shorting in the coil. Compare with the spec for your engine where the service manual lists one, but trust the comparison first.
- Watch the circuit while flexing the rear harness
With the engine idling, back-probe injector 12's control wire with a scope (port injection only) or watch live misfire data, then flex the rear harness a little at a time. A trace that collapses to ground, or a stumble when one spot moves, locates the chafe more precisely than any visual inspection.
- Swap to confirm, then replace and retest the driver
Moving injector 12 to another position on the same rail is the definitive test; if the code follows it, replace it. If the fault stays with cylinder 12 after the wiring checks out, the module's driver may be failing — on dual-module engines, that's the module controlling cylinder 12's bank.
DIY or shop? The scan, bank-wide code check, and visual inspection are worth doing yourself even on a twelve-cylinder car, because they can point a shop straight to the fault. Past that, cylinder 12's spot against the firewall usually means removing covers, cowl panels, or the intake just to see the injector, and a swap test doubles that labor. Most owners should hand over the hands-on work once the plenum has to come off, especially on an engine they haven't worked on before.
Tools for the DIY steps: Scan tool that reads all engine modules · Digital multimeter · Lab scope with back-probe leads · Flashlight and inspection mirror · High-temperature harness sleeve
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0294.
Start a case with P0294 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0294?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0294: common questions
Which engines can set P0294?
Only twelve-cylinder engines — V12s and W12-style layouts. There is no cylinder 12 on anything smaller, so this code simply cannot occur on four-, six-, eight-, or ten-cylinder vehicles.
Is P0294 a clogged injector?
No. A clog is mechanical and invisible to this monitor, which watches circuit voltage. P0294 means the cylinder 12 injector circuit read electrically low — short to ground, broken wire, or shorted injector coil. The fix is electrical, not a cleaning service.
Why fix it if the car drives beautifully?
Because a V12 masking the misfire doesn't stop the chemistry: unburned fuel from cylinder 12 can overheat that bank's catalytic converter, and exhaust repairs on twelve-cylinder cars cost multiples of an injector or harness fix. The warning light is the only symptom you may get.
What's the first test a shop will run?
Usually injector resistance: unplug cylinder 12's injector, measure it, and compare with a neighbor. That single measurement splits the problem — matching values send the diagnosis to the harness and connector, while a shorted or open reading condemns the injector itself.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0294 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0294 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.