Faulty ignition coil for cylinder 6 (most common); Damaged or corroded wiring or connector at the coil; Open or shorted feedback circuit between the coil and PCM; PCM driver circuit failure (rare but possible); Poor ground connection for the ignition coil; Aftermarket or incorrect coil installed that does not provide proper feedback

DTC codes / GM codes / P1366

P1366 · GMIC Cylinder 6 Not Toggling After Enable

Q: What does code P1366 mean?

IC Cylinder 6 Not Toggling After Enable. P1366 on GM vehicles means the powertrain control module (PCM) has commanded the ignition coil for cylinder 6 to fire, but the coil's feedback circuit is not toggling between high and low voltage as expected. The PCM detects this lack of switching after the enable signal is sent, indicating a fault in the coil, its wiring, or the feedback circuit itself.

P1366 on GM vehicles means the powertrain control module (PCM) has commanded the ignition coil for cylinder 6 to fire, but the coil's feedback circuit is not toggling between high and low voltage as expected. The PCM detects this lack of switching after the enable signal is sent, indicating a fault in the coil, its wiring, or the feedback circuit itself.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Check engine light (malfunction indicator lamp) illuminated
Engine misfire or rough running, especially under load
Noticeable loss of power or hesitation during acceleration
Shaking or vibration from the engine bay
Often no symptoms besides the warning light, especially if the misfire is subtle

Common causes, most likely first

Faulty ignition coil for cylinder 6 (most common)
Damaged or corroded wiring or connector at the coil
Open or shorted feedback circuit between the coil and PCM
PCM driver circuit failure (rare but possible)
Poor ground connection for the ignition coil
Aftermarket or incorrect coil installed that does not provide proper feedback

How to diagnose and fix it

Perform a visual inspection of the cylinder 6 coil, connector, and wiring for damage or corrosion
Swap the cylinder 6 ignition coil with a known-good coil from another cylinder and see if the code moves
Check for spark at cylinder 6 using a spark tester or by swapping coils
Use a multimeter to check continuity and resistance of the feedback circuit between the coil and PCM
Inspect and clean the coil ground connection; verify ground integrity
If the coil is faulty, replace it with an OEM-quality part
If wiring or PCM is faulty, repair wiring or replace PCM as needed

What the feedback circuit is telling you

The 'IC' in the definition stands for Ignition Coil, and the feedback signal is a small current that toggles as the coil fires; a coil can still spark while failing to toggle, leading to a code without a noticeable misfire.
A common misdiagnosis is replacing the coil when the real problem is a chafed wire in the harness near the coil or a loose ground, so always check the circuit before condemning the coil.
On some GM engines, the ignition coil feedback circuit is shared with other cylinders, so a fault in one coil can affect the feedback of another; check for codes for other cylinders as well.
Aftermarket coils sometimes lack the proper feedback circuitry, causing P1366 even though the engine runs fine; always use OEM or equivalent coils.
The PCM may set P1366 only after the engine has run for a certain time and reached operating temperature, so intermittent faults can be missed during a quick scan.

Can I keep driving with P1366?

You can usually drive the vehicle with P1366, but if you notice a misfire or rough running, avoid heavy acceleration and have it diagnosed soon to prevent damage to the catalytic converter from unburned fuel.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.