P0305 Code on a GMC: Cylinder 5 Misfire Detected (GMC Guide)

P0305 on a GMC is GM's "Cylinder 5 Misfire Detected," and only GMCs with five or more cylinders can set it: the V6 and V8 Sierras, Yukons and Savanas, the V6 Acadia, Terrain and Canyon, the inline-five Canyon and the inline-six Envoy. Cylinder 5 means something different on each. On a 2017-and-later Acadia or Canyon V6, it's one of the two cylinders GM shuts off for fuel economy. On the 3.5L or 3.7L five-cylinder Canyon, it's the last cylinder in the row, the one GM's fuel-contamination bulletin calls the "opposite end." The surprise: on a V8 Sierra, Yukon or Savana that just had engine work, GM has a document about P0300 caused by the cylinder 5 and 7 injector connectors being plugged in crossed, a misfire the monitor may not even catch. This guide covers where cylinder 5 is on each GMC engine and what GM has published about it.

What Does P0305 Mean on a GMC?

The ECM tracks crankshaft speed between firing events. When cylinder 5's power stroke repeatedly fails to accelerate the crank, it logs P0305, usually with P0300. A four-cylinder Terrain, Acadia or Canyon can't set it, so if you see P0305 on one of those, re-check the code. If several cylinders are counting, start at our P0300 GMC hub. GM's general misfire monitor is explained in our P0300 GM guide.

Where Cylinder 5 Is on Your GMC

On a transverse Acadia, cylinder 5 is on the rear bank, so it's harder to reach than its partner AFM cylinder 2 on the front bank. That matters for GM's test, which swaps parts between the two banks.

Acadia and Canyon V6: Cylinder 5 Is an AFM Cylinder

GM's 21-NA-036 says cylinders 2 and 5 are the active fuel management cylinders on the 3.6L LGX and LGZ, naming the 2017–2022 Acadia and Canyon with P0300, P0302 and P0305. GM's two causes are oil leaking past the AFM oil control valve solenoid in the cam cover, so the cylinder deactivates from oil bleed-off, and rockers that don't latch.

The swap test, from the cylinder 5 side

PIP5824D (2021–2023 Acadia, 2021–2022 Canyon) describes misfires on cylinder 2 or 5 that can happen all the time, after an AFM event, or on a cold start. GM's correction starts with no parts at all: swap the AFM rocker oil control solenoid side to side between the cam covers. If the misfire goes away or moves to the other bank — P0305 becoming P0302 — replace the solenoid. If it stays on cylinder 5, remove that bank's cam cover (the rear cover on an Acadia, the passenger-side cover on a Canyon) and turn the engine by hand while watching the valves. If a valve doesn't open, GM replaces all four rockers (SRFFs) and all four lash adjusters for that cylinder. Our P0302 GMC guide covers the same test from the other side.

P219A can be a cylinder 5 problem

Not every damaged cylinder 5 rocker sets P0305. GM's 22-NA-193 (2017–2024 Acadia LGX, Canyon LGZ) covers P219A and P219B air-fuel imbalance codes and says injectors usually pass GM's AFIT test. Its instruction is to remove the cam cover of the affected bank ("A is Bank 1, B is Bank 2") and inspect the lash adjusters and rockers "for cylinder 5 or cylinder 2." Because cylinder 5 is on bank 1, a P219A on an Acadia or Canyon V6 points to cylinder 5's valvetrain.

Solenoid wiring and early builds

17-NA-292 covers 2017–2018 Acadia and Canyon V6s with P3409 and/or P3433 from a wiring issue on the cylinder 2 and/or cylinder 5 deactivation solenoid circuits. If the vehicle was built between April 13 and August 7, 2017, GM replaces both the right- and left-bank solenoids (12679721, quantity 2). Outside that window, the first check is the connector terminals. PIP5493G (2017–2019 Acadia and Canyon) adds broken or dislodged rockers and bent camshaft actuator pins on the misfiring bank, and says to replace the AFM solenoids in both cam covers if broken parts are found.

Cold-start misfire on cylinder 5

On every 3.6L Acadia, the 2010–2017 Terrain V6 and the 3.6L Canyon, GM's 18-NA-115 describes a cold-start misfire "always occurring on one or two cylinders" that fades as the engine warms, from block porosity letting coolant in at the liner-to-deck face. On a Gen 2 V6 that also has AFM hardware on cylinder 5, separate the two: a coolant leak tends to show on a cold-soaked pressure test and a blacklight borescope, while a solenoid problem follows the swap.

Five-Cylinder Canyon: The End Cylinder

The 2004–2012 Canyon was offered with GM's Atlas inline five, the 3.5L L52 and later the 3.7L LLR. Cylinder 5 is at the back of the block. GM's PIP3472C explains why it gets singled out: these engines have a returnless fuel rail, so contaminants can stay trapped in the rail. GM says they pass through the number 1 injector during deceleration "and through the opposite end fuel injector on acceleration," and that "the injector at the end will depend on the RPO of the engine (4, 5 or 6 cylinder in-line engine)." On the five-cylinder Canyon, that end injector is cylinder 5. A P0305 that appears during or after hard acceleration fits the pattern. GM's correction is to clean the tank, lines and rail, then the injectors, and it warns that a sticking valve can remain. GM also says fuel-contamination repairs are not warranty repairs.

A single-cylinder misfire at idle only is a different document. GM's PIP4013D (2006–2012 Canyon, 2005–2009 Envoy inline engines) blames a damaged valve, valve seat or piston ring. GM asks for a leakage test with the piston held at top dead center and the air regulated to 50–60 psi. If a cylinder head is replaced, GM warns that installing it with the camshafts in place, without the J44221 camshaft holding tool or without the #1 piston at TDC, can bend a valve and leave an idle misfire that looks like the original problem.

NHTSA's summaries also list an early GM special coverage, 03039, for the 2004 Canyon with misfire and possible P0300–P0305, with a reference to an engine exchange program. We could not read the GM document itself, and any coverage from that era has long since ended for practical purposes. A dealer VIN check is still free.

Cylinder 5 on the Sierra, Yukon and Savana

On AFM V8s, GM deactivates cylinders 1, 7, 6 and 4 (20-NA-038), so cylinder 5 always fires, and on the 4.3L LV3 it's 3 and 6. A P0305 on these trucks points first at ignition, injectors and connections. The most cylinder 5-specific GM document is PIP5169, which covers 1999–2013 Savana, Sierra and Yukon, 2002–2014 Sierra HD, 2003–2009 Envoy and 2009–2013 Canyon V8s. GM says P0300 can set after engine repairs because the injector connectors for cylinders 5 and 7 (and 6 and 8) were crossed, that the misfire may not be detected, and that it may happen on deceleration. Cylinders 5 and 7 are neighbors at the rear of the driver-side bank. If your truck started misfiring right after an intake, head or harness job, check the injector connector routing against the service information first.

Other truck documents apply to cylinder 5 like any other cylinder: PIP4819A (2010–2013 Sierra, Yukon, Savana and Canyon V8s, P0300–P0308) for a plug wire loose at the coil, PIP5159C for a missing "C" clip on 2014–2019 Sierras and 2015–2019 Yukons, and GM's lifter documents for DFM trucks, where any cylinder can deactivate.

Symptoms of P0305

• Check engine light, flashing during a heavy misfire
• Roughness after cruising on an Acadia or Canyon V6 (V4 mode exit)
• A stumble during or after hard acceleration on a five-cylinder Canyon
• A misfire that appeared right after engine work on a V8 truck
• A cold-start miss that clears when warm on a 3.6L
• Companion codes: P219A, P3409/P3433 or P0016–P0019 on a Gen 2 V6; P0205 or P0355 (cylinder 5 injector or coil circuit)

Causes and How to Confirm Each

How Is P0305 Diagnosed on a GMC?

1. Confirm the engine. P0305 needs a V6, V8, inline five or inline six. Read the RPO code on the glovebox label.
2. Record when it misfires: after V4 mode, under hard acceleration, at idle, cold only, or since a recent repair.
3. Swap the coil and plug and test the injector before anything else.
4. On a Gen 2 V6, swap the AFM solenoids and see whether the code becomes P0302. Check for P219A and P3433.
5. On a five-cylinder Canyon, inspect the fuel rail and tank for contamination if the miss follows hard acceleration.
6. On a V8 after engine work, verify the cylinder 5 and 7 injector connectors.
7. Watch the valves or run leak-down if the misfire stays on cylinder 5.
8. Check your VIN for open bulletins and recalls, then confirm the repair under the conditions that set the code.

Parts and Cost

GM Documents That Name P0305 or Cylinder 5 on GMC Models

Have a dealer check your VIN for open recalls, bulletins and special coverages. The check is free.

What Other Pages Get Wrong

• "P0305 can happen on any engine." A four-cylinder Terrain, Acadia or Canyon has no cylinder 5.
• "Buy a new AFM solenoid." GM's PIP5824D test swaps the two solenoids first. If the misfire moves to cylinder 2, you know which part to buy.
• "P219A means injectors." On the Acadia and Canyon V6, GM's 22-NA-193 points to cylinder 5's lash adjusters and rockers.
• "New misfire after a repair means a new failure." GM's PIP5169 says crossed cylinder 5 and 7 injector connectors on a V8 can cause it.
• "Clean the injectors and you're done" on a five-cylinder Canyon. GM says the whole tank and rail must be cleaned or the problem comes back.

Frequently Asked Questions

Where is cylinder 5 on a GMC Acadia V6?

On the rear, firewall-side bank (bank 1), at the transmission end. It's one of the harder cylinders to reach.

Why does my Canyon V6 misfire on cylinder 5 after highway driving?

On 2017-and-later Canyon V6s, cylinder 5 deactivates in V4 mode. GM's documents describe misfires after an AFM event from a leaking solenoid or rockers that don't re-latch.

My old five-cylinder Canyon misfires on cylinder 5 when I floor it. Why?

GM's PIP3472C says contaminated fuel trapped in the returnless rail passes through the end injector under hard acceleration. On the 3.5L and 3.7L, that's cylinder 5.

Can a Sierra V8 get P0305 from AFM?

Not on AFM engines, where cylinder 5 always fires. On DFM engines (5.3L L84, 6.2L L87), any cylinder can deactivate, so a lifter is possible.

My truck started misfiring right after a repair. What should I check?

On a GMC V8, GM's PIP5169 says to verify the injector connector routing, because cylinders 5 and 7 (and 6 and 8) can be crossed.

Can I drive with P0305?

If the light is flashing, reduce load and have it checked soon to protect the catalytic converter. A steady light still needs diagnosis before a small valvetrain fault grows.