Rick's Free Auto Repair Advice

P0300 chirp, squeak, squeal or tick noise GM

Fix P0300 chirp, squeak, squeal or tick noise GM

GM has issued a service bulletin #PIP4138J to address a check engine light, P0300 chirp, squeak, squeal or tick noise on the GM vehicles listed below with a V-8 engine


2004-2007 Buick Rainier

2008-2009 Buick LaCrosse, Allure (Canada Only)

2006-2007 Cadillac CTS-V

2002-2010 Cadillac Escalade

2010 Chevrolet Camaro

2002-2010 Chevrolet Avalanche

1999-2010 Chevrolet Express, Silverado, Suburban, Tahoe

2009-2010 Chevrolet Colorado

2003-2009 Chevrolet Trailblazer

2006-2010 Chevrolet Impala SS

2006-2007 Chevrolet Monte Carlo SS

2003-2006 Chevrolet SSR

2005-2010 Chevrolet Corvette

2009-2010 GMC Canyon

2003-2009 GMC Envoy

1999-2010 GMC Savana, Sierra, Yukon

2003-2010 Hummer H2

2008-2010 Hummer H3

2008-2010 Pontiac G8

2005-2006 Pontiac GTO

2005-2008 Pontiac Grand Prix GXP

2005-2009 Saab 97x

P0300 and other symptoms

GM reports that you may find a P0300 random misfire code as well as codes P0300-P0308. The misfires may occur on a single cylinder and may or may not be felt during driving and may be accompanied by a chirp, squeak, squeal or tick noise.

If you hear any of those noises, testing by shutting off individual fuel injectors will not help, so don’t bother. The noise usually occurs at camshaft speed, which is half the speed of the crankshaft.

Cause of P0300 chirp, squeak, squeal or tick noise

GM has determined that the cause may be any of the following:

• worn camshaft lobe and/or lifter roller

• a sticking valve

• valve leakage

• a broken valve spring

• a collapsed AFM (Active Fuel Management) lifter.

Diagnose a worn cam lobe or lifter roller

GM states that a worn cam lobe creates a consistent chirp, camshaftsqueak, squeal, or tick noise at camshaft speed, along with a misfire with trouble codes P0300-P0308. You may or may not feel the misfire. The misfire can occur at all RPMs or just a specific RPM, such as idle only or only at high RPM.

Since the noise and misfires are the result of a worn cam lobe or lifter roller, disabling a fuel injector or performing a static compress test or cylinder leakage will not be conclusive. Compression and cylinder leakage tests will show acceptable results on all cylinders since the engine is not rotating.

GM recommends following this procedure to diagnose a worn cam lobe or lifter roller:

Test 1

Remove the valve covers and use a wooden hammer handle to apply pressure to the rocker arms while the engine is running. Apply pressure to identify which rocker arm is making the noise. Apply pressure to the push rod side of rocker, valve side of rocker and listen for the noise to stop. If the noise changes or stops while applying pressure, the cam lobe or lifter roller for that cylinder is the most likely cause of the problem. However, GM warns that this procedure is not accurate 100% of the time and the accuracy depends on the amount of cam lobe wear.

Test 2 Disconnect rocker and push rod one cylinder at a time

Disconnect the ignition coils and injectors on one bank of the engine. Then run the engine with the valve cover removed. While running, loosen each rocker arm by a couple of turns and

listen for a change in the noise. Or, you can remove one rocker, push rod, ignition coil, and fuel injector at a time and run the engine to see if the noise disappears. If the noise goes away, and you’ve confirmed valve spring, push rod and rocker arm are in good condition, then the cause is most likely a worn cam lobe or lifter roller.

Test 3

Measure the cam lobe lift at the push rod side of the rocker arm. The lift will differ from the shop manual specifications due to wear. But the lift should be similar when compared to other intake and exhaust push rods. The misfiring or ticking cylinder push rod would have less lift than the other cylinders if the cause is a worn lifter roller or worn cam lobe.

Another possibility of no/low lift on cylinders 1, 4, 6, or 7 on an engine with active fuel management (AFM) could be a collapsed AFM lifter. If you suspect a collapsed AFM lifter, refer to PIP4568 for additional information.

Test 4 for engines with active fuel management

Using your scan tool, command AFM on with the engine running. That will unlatch the lifters on cylinders 1, 4, 6, and 7. The valves on those cylinder will stop opening. If the noise goes away when you do this, there is a good chance that the noise is coming from the valvetrain of cylinders 1, 4, 6, or 7, thus isolating the problem to just those cylinder.

Next, check the push rods, rockers, or valve springs for those cylinders. If they check out in good condition, then the noise is most likely caused by a worn lifter roller and/or cam lobe on cylinders 1, 4, 6, or 7.

However, if the above tests above do not isolate the cause of the noise, it may be necessary to tear down the engine further to visually inspect the lifter rollers and cam lobes for obvious damage, such as flat spots, pits, grooves. scoring, gouging, flaking, rusting, etc.

GM warns that it is very easy to overlook a damaged cam lobe when inspecting them through the lifter bores. Just because the lifter rollers are not worn, does not mean that the cam lobes are okay. Both components must be carefully inspected.

If you detect a worn cam lobe or roller lifter on an engine with AFM, you should also inspect the VLOM (Valve Lifter Oil Manifold) screen for debris, which is located in the VLOM below the oil pressure sensor. Clean the VLOM screen if any debris is present.

Test 5 Check for a sticking valve

A sticking valve can cause an engine misfire that may or may not be felt and it may occur consistently or intermittently. If the cause is a sticking valve, it’s unlikely that it will produce engine noise. The misfire may be temperature sensitive and it may be more apparent during certain operating conditions, such as driving up a grade, cresting a hill, or during hard acceleration.

Signs of a sticking valve

If the engine misfires continue to increase during aggressive deceleration with engine braking, or if the misfire occurs consistently, a static compression test, running compression test or cylinder leakage test may isolate the sticking valve.

But, it is unlikely that any of these tests will isolate the sticking valve if the misfire only occurs while driving at specific conditions.

Test 6 Test individual valves for sticking

Remove the spark and insert an air chuck into the spark plug hole. Connect to shop air. Remove the valve spring and valve keepers and wrap a rubber band around the valve keeper grooves to prevent the valve from falling into the cylinder.

Release the air pressure from the cylinder and work the valve up and down in the guide while turning the valve 360 degrees. If you feel any binding is felt, you’re dealing with a stem to guide clearance issue which must be repaired.

If you don’t detect any sticking, rotate and snap the valve onto the valve seat to make sure that it easily comes off seat easily. If you have to use force to tap the valve off of the seat, excessive carbon build up exists, which may be repaired by decarboning the engine. Refer to the latest version of PIP4753 for decarboning instructions.

Test 7 Test for valve leakage

Valve leakage on this engine generally causes a consistent engine misfire that may or may not be felt. Plus it most often occurs at idle or low RPM. In addition, valve leakage usually doesn’t cause engine noise. Conduct a Cylinder Leakage Test to detect excessive leakage.

Test 8 Test for a broken valve spring

A broken valve spring on this engine usually causes ticking noise and an engine misfire and may occur consistently or intermittently. If it is causing an engine misfire, it may or may not be felt and it may only occur at specific operating conditions, such as high RPM driving, etc.

In some instances, a static compression test, running compression test, and/or cylinder leakage test may isolate the broken valve spring, while in other instances where the concern is intermittent, it may not if the spring remains stacked together during the tests.

It may be necessary to visually inspect the valve springs by closely examining them. Sometimes, the two broken pieces of the spring will remain stacked together so it may be hard to detect when visually inspecting them. As a result, it may help to lightly push on different places on the springs with a small hammer handle. If a broken valve spring is found, replace the broken valve spring as necessary.

Test 9 Check for a collapsed AFM Lifter (Engines with AFM Only):

If an AFM lifter unlocks as soon as the engine is started, a SES light and DTC P0300 will be found but it is unlikely that any noise will be heard. If an AFM lifter is mechanically collapsed/stuck, a consistent valve train tick noise, SES light, and DTC P0300 will be experienced with engine misfires on cylinder 1, 4, 6, or 7. If either of these AFM lifter concerns is suspected, please refer to the latest version of PIP4568 for additional information.

©, Rick Muscoplat

Posted on by Rick Muscoplat


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