P0268

Cylinder 3 Injector Circuit High

P0268 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 3 Injector Circuit High. It is logged by the engine control unit when the fuel/inj monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code

P0268

Group

Powertrain

System

Fuel/Inj

Severity

Warning (MIL on, possible limp mode)

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What P0268 means

P0268 is triggered when the ECM detects that the cylinder 3 injector control circuit voltage remains higher than expected during the period the driver transistor should be grounding it. In a healthy injector circuit the ECM's internal driver pulls the control line to near-ground when commanding the injector open; if that line stays elevated — because battery voltage is back-fed through a shorted harness wire or because the ECM driver transistor has failed in the on position — the ECM recognises the discrepancy and sets P0268.

A short to battery voltage in the injector harness is the most common external wiring cause: a chafed wire touching a 12 V feed or an adjacent circuit can hold the control line high and prevent the ECM from detecting the normal low-side voltage collapse that confirms the injector fired. Internally, a solenoid winding that has partially shorted can drop the coil's resistance outside the ECM driver's safe operating range, producing an abnormal voltage signature that triggers the high-circuit threshold.

With a circuit-high fault active, cylinder 3 may receive excessive, insufficient, or erratically timed fuel, causing rough idle, misfires, and elevated hydrocarbon emissions. Unresolved faults of this type can cause catalyst overheating and eventual damage, so prompt diagnosis is warranted.

Common causes

Most-frequently reported root causes when P0268 is logged.

1
Short circuit to battery voltage in the wiring harness between the ECM and the cylinder 3 injector, back-feeding the control line high.
2
Failed ECM injector driver transistor for cylinder 3 stuck in the energised (conducting) state, holding the line high despite no command.
3
Internal solenoid winding short inside the cylinder 3 injector reducing coil resistance below the ECM driver's minimum threshold.
4
Corroded or high-resistance connector at the cylinder 3 injector causing the ECM to measure an elevated voltage due to resistive drop in the circuit.
5
Water or oil contamination inside the injector connector creating leakage paths that artificially raise the measured circuit voltage.
6
Adjacent chafed wiring conducting battery voltage onto the cylinder 3 injector signal wire intermittently.
7
Incorrect replacement injector fitted with a coil impedance incompatible with the ECM's drive strategy (e.g. saturated driver receiving a peak-and-hold injector).

Symptoms drivers notice

MIL illuminated with P0268 stored; a flashing MIL indicates an active severe misfire on cylinder 3.

Rough idle and noticeable engine vibration attributable to cylinder 3 firing abnormally.

Hesitation and stumble on acceleration, particularly from rest or at low throttle openings.

Reduced engine power and slower throttle response under load.

Possible fuel smell from the exhaust if cylinder 3 receives an uncontrolled fuel pulse.

Increased hydrocarbon emissions and potential catalytic converter overheating if raw fuel enters the exhaust stream.

How to diagnose P0268

A typical diagnostic flow when this code is present.

1
Scan for all stored codes and freeze-frame data; confirm P0268 is present and note any companion P0303 misfire or P0263/P0264 codes that could indicate a related pattern.
2
Visually inspect the cylinder 3 injector connector and harness for chafing, melted insulation, or contact with adjacent high-voltage or battery circuits; repair obvious damage before proceeding.
3
Disconnect the cylinder 3 injector and measure solenoid resistance with an ohmmeter — compare against OEM specification (typically 12–16 Ω saturated or 0.5–2 Ω peak-and-hold); a value below minimum indicates a shorted winding.
4
With the injector disconnected and ignition on (engine off), backprobe the ECM driver wire at the harness connector and measure voltage to ground — any significant voltage present on the driver wire when the ECM is not commanding injection indicates a short to battery voltage in the harness.
5
Use a lab-scope to capture the injector drive waveform while cranking or at idle — a normal high-impedance injector shows a rapid voltage collapse to near ground during the pulse; a line that stays elevated confirms the circuit-high condition and narrows the fault to the harness or ECM driver.
6
Swap the cylinder 3 injector with a known-good unit to rule out an internal solenoid short; if the fault stays on cylinder 3 position after the swap, the fault is in the harness or ECM.
7
After repairs, clear all codes, run a drive cycle that exercises both idle and loaded conditions, and rescan to confirm P0268 does not return.

Related powertrain codes

Frequently asked questions

Why does a high-circuit fault (P0268) still cause a misfire on cylinder 3 if the injector is held open?

If the control line is held permanently high by a short to battery voltage, the ECM driver cannot pull it low, meaning it cannot actually open the injector at all — the injector remains shut. The 'high' refers to the voltage the ECM reads on its driver output, not whether the injector is mechanically open. The result is no fuel delivery to cylinder 3, causing a misfire just as an open-circuit low fault would.

Can a failed ECM driver cause P0268 even when the wiring and injector are fine?

Yes. The ECM uses an internal transistor to switch the injector's control line low. If that transistor fails in the conducting state it holds the output pin in a driven-high condition. A lab-scope will show the drive line staying elevated regardless of injector command. If harness and injector tests are normal, ECM driver failure should be suspected and the ECM bench-tested or replaced.

What is the difference between P0267 and P0268 on cylinder 3?

P0267 (circuit low) means the control line is being held at ground when the ECM expects it to be at supply voltage during the off-state — indicating an open circuit or short to ground. P0268 (circuit high) is the reverse: the line stays elevated when the ECM is trying to pull it low — indicating a short to battery voltage or a stuck-on ECM driver. The repair approach is different for each.

Does P0268 damage the fuel injector or ECM if left unrepaired?

A sustained short to battery voltage through the injector driver circuit can overheat the ECM's output transistor and cause permanent ECM damage over time, particularly if the short is low-impedance. The injector itself may also overheat if excess current flows through a partially shorted coil. Early diagnosis and repair protects both components.

Disabling P0268 in software

RaceTune can permanently disable P0268 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent

The monitor is disabled in the ECU itself — not just cleared. It cannot return.

Tailored to your file

Each patch is matched to your specific software version — never a one-size-fits-all file.

Reversible

The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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