P0306 Code on a Cadillac: Cylinder 6 Misfire Detected (Cadillac Guide)

P0306 on a Cadillac is "Cylinder 6 Misfire Detected." Like P0305, it can only set on a Cadillac V6 or V8. The four-cylinder ATS, CTS, CT4, CT5, CT6, XT4, XT5 and XT6 have no cylinder 6. Cylinder 6 is also the cylinder GM opened an engineering investigation on for the 2017 Cadillac XT5. GM's PIP5493 told dealers that a first-time P0306 on an XT5 should be cleared and re-driven, without replacing parts, and that it could appear after a cold start, a short drive and a hard highway merge. On the Escalade, cylinder 6 is one of the AFM cylinders. GM documents it alongside cylinder 4 for collapsed lifters, alongside cylinder 8 for crossed injector connectors after engine work, and in a 2025 coil bulletin that warns against blaming the injector. This guide covers all of it.

What Does P0306 Mean on a Cadillac?

The ECM counts a misfire whenever cylinder 6's power stroke fails to speed up the crankshaft as expected. Enough of them sets P0306, usually with P0300. For multi-cylinder misfires, use our P0300 Cadillac hub.

Which Cadillacs Can Set P0306

• Yes: all Cadillac V6 engines (3.6L, 3.0L, 2.8L turbo, the twin-turbo V6s and the Catera 3.0L) and all Cadillac V8s (Northstar, Escalade, CTS-V, CT5-V, CT6 4.2L).
• No: any four-cylinder Cadillac, and Cadillac EVs.

Where Cylinder 6 Is on Your Cadillac

On a transverse XT5 or XT6, cylinder 6 is on the front bank, so its coil is easier to reach than cylinder 5's. That makes the coil swap test quick.

The 2017 XT5 Cylinder 6 Investigation (PIP5493)

GM's PIP5493 series (first released April 2017) covered misfires with P0300 and P0301–P0306 on Gen 2 V6 engines. In NHTSA's summary, GM describes it as covering "engineering investigations into cylinder 6 misfire on XT5." The June 2017 version, PIP5493B, gave XT5 dealers this specific instruction:

• If it is the first visit for a P0300 or P0306 misfire in history on cylinder 6, clear the codes. Drive the vehicle under the conditions the customer described.
• If the conditions are unknown, GM described the typical trigger on the XT5: a cold start, a one-to-three-mile drive to a highway, then heavy acceleration to merge.
• If that reproduces it, do not replace any parts. Document the driving conditions on the repair order. "Engineering is aware of this specific condition and is working on a solution."
• If it's a repeat concern, follow normal service diagnostics.

By August 2018, PIP5493G had replaced that with a broader procedure for the 2016–2019 ATS, CTS and CT6 and the 2017–2019 XT5:

1. On 2016–2017 vehicles, confirm the latest ECM calibration and reprogram if a related one is available. GM said not to reflash 2018 vehicles for this.
2. Test the spark and fuel components normally: coil grounds and wiring, injectors, plugs.
3. Inspect for broken or dislodged rockers (SRFFs) while turning the engine by hand. The camshaft carrier may have to come off.
4. Remove the camshaft actuators on the misfiring bank and look for a bent actuator pin or camshaft damage.
5. If broken parts are found, replace them and the AFM oil control valves in both cam covers. On vehicles built before November 1, 2017, also replace the exhaust lash adjusters on the misfiring cylinder.

GM separately issued PIE0391 for 2017 XT5 LGX engines with a repeat P0300 visit. Dealers were asked to capture a GDS2 session without clearing the code and to contact engineering. The PIP5493 series itself has since been replaced by 21-NA-278, which lists P0306 among the codes for spongy lash adjusters, damaged rockers or actuators, and a left-bank timing chain tensioner gasket. Cylinder 6 is on the left bank (bank 2).

Escalade: Cylinder 6 Lifters, Wires and Coils

AFM lifters

GM's 20-NA-038 lists cylinder 6 as a deactivating cylinder on the 2015–2020 Escalade L86 and the LT4 engines. PIP5259D names "cylinder 4, 6" on the 2015 Escalade 6.2L, caused by collapsed AFM lifters from oil aeration. GM replaced that bank's AFM lifters and guide plus the oil pump pick-up seal. PIP4568S covers cylinders 1, 4, 6 and 7 on 2007–2014 AFM Escalades, and 15-06-01-002O covers 2015–2020. Our P0304 guide walks through GM's AFM compression test.

Crossed injector connectors 6–8

PIP5169 (2002–2013 Escalade, 2006–2013 CTS-V) says that after engine repairs, injector connectors can be swapped between cylinders 6 and 8 (and 5 and 7). The resulting misfire may only happen on deceleration. A P0306 that appeared right after intake or injector work deserves this check before anything else.

Plug wires and coils

• PIP4819A (2010–2013 CTS-V and Escalade): P0300–P0308 from a plug wire loose at the coil. Replace that cylinder's wire.
• PIP5159C (2015–2019 Escalade L86, 2016–2019 CTS-V LT4): loose plug wire at the coil, often from a missing or damaged "C" clip.
• PIP5298B (2015–2019 Escalade L86): loose terminal tension on the ignition coil power feed causing P0300 and rough running.
• PIP6073 (June 2025): 2025 Escalade 6.2L L87 or LT4 and 2025 CT5-V Blackwing with P0300–P0308 from a faulty ignition coil. GM says to swap the coil with an adjacent one and make sure the plug wire is fully seated. It warns not to replace injectors or the ECM unless testing proves them faulty, noting that injectors returned for this concern were inspected and no trouble was found. The coil part number GM lists is 12726023.

Symptoms of P0306

• Check engine light after a cold start, short drive and hard merge (2017 XT5 pattern)
• Misfire on cylinders 4 and 6 with a tick (Escalade AFM lifter pattern)
• Rough running that started after engine work (crossed injector connectors)
• An intermittent stumble that a coil swap moves (Escalade coil and wire bulletins)
• Flashing light during heavy misfire

Causes and How to Confirm Each

How Is P0306 Diagnosed on a Cadillac?

1. Confirm it's a V6 or V8 and locate cylinder 6 on GM's diagram.
2. Note recent repairs. If injectors or the intake were just off a V8, verify the injector connectors first.
3. Swap the coil with a neighbor and re-seat the plug wire (V8). If the misfire moves, you're done.
4. Test the injector before replacing it. GM's 2025 coil PI specifically warns against unnecessary injector replacement.
5. On an Escalade with AFM, run the AFM compression test and check for a tick at camshaft speed.
6. On a Gen 2 V6, check the calibration level (2016–2017), then inspect rockers and the bank 2 camshaft actuator per GM.
7. Reproduce the conditions — on an XT5, GM's cold-start, short-drive, hard-merge sequence.
8. Check your VIN for current bulletins and recalls.

Parts and Cost

GM Documents That Name P0306 or Cylinder 6 on Cadillacs

Have a dealer check your VIN for open recalls and bulletins. The check is free, and it is more reliable than any article, including this one.

What Other P0306 Pages Get Wrong

• "A misfire code means a part has failed." GM's first instruction for a first-time 2017 XT5 cylinder 6 misfire was to clear it and re-drive, without replacing parts.
• "Replace the injector if the coil swap doesn't help." GM's 2025 Escalade PI says returned injectors were inspected and no trouble was found. Test first.
• "Cylinder 6 is on the same bank as cylinder 5." On every Cadillac V6, cylinder 5 is on bank 1 and cylinder 6 is on bank 2.
• Ignoring the last repair. GM documents crossed 6–8 injector connectors after engine work on V8s.

Frequently Asked Questions

My 2017 XT5 set P0306 merging onto the freeway. Is something broken?

Not necessarily. GM described that exact pattern (cold start, short drive, hard merge) in PIP5493B and told dealers not to replace parts on a first occurrence. If it comes back, normal diagnostics apply, and later GM documents point to rockers and cam actuators.

Where is cylinder 6 on an XT6?

On the front, radiator-side bank at the transmission end. It's the easier bank to reach on the transverse V6.

Does AFM turn off cylinder 6 on my Escalade?

Yes on 2007–2020 Escalades with AFM. GM lists cylinders 1, 4, 6 and 7. On the 2021+ L87, any cylinder can deactivate.

P0306 started right after my injectors were replaced. Why?

GM's PIP5169 documents injector connectors crossed between cylinders 6 and 8 (and 5 and 7) after engine repairs on Escalade and CTS-V V8s. Check the routing against the service information.

Which coil does GM list for the 2025 Escalade misfire PI?

PIP6073 lists ignition coil 12726023. Confirm fitment for your VIN, and replace it only after a swap test shows the coil is at fault.

Can a four-cylinder Cadillac show P0306?

No. Four-cylinder Cadillacs only have cylinders 1–4. A P0306 reading on one means the tool or the vehicle record is wrong.