P0300 Code, What to try next? - TerrainForum.net: GMC Terrain Forum
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post #1 of 12 (permalink) Old 08-20-2019, 11:16 AM Thread Starter
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P0300 Code, What to try next?

For the last two months I have been battling the dreaded P0300: Random Multiple Misfire Detected.

So far I have replaced plug and ignition coils, and the intake and exhaust solenoids (a different code).

2010 Terrain SLE 2.4L I4

Any ideas on what I should look for next?

Thanks!

2010 Terrain SLE 2.4L I4 FWD Onyx Black

Last edited by brisket_lover; 08-20-2019 at 11:42 AM.
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post #2 of 12 (permalink) Old 08-20-2019, 11:18 AM
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It would help to know year and power train.

2018 Equinox LT1 1.5 L 4 cyl, AWD, S/R Cajun Red Tintcoat/Black

2010 Equinox LTZ 2.4 L 4 cyl, FWD, S/R Cardinal Red/Black
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post #3 of 12 (permalink) Old 08-20-2019, 11:41 AM Thread Starter
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2010 Terrain SLE 2.4L I4 , sorry it was in my signature but it would be helpful in the post.
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2010 Terrain SLE 2.4L I4 FWD Onyx Black
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post #4 of 12 (permalink) Old 08-20-2019, 11:59 AM
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Throttle or Idle Learn
Description
The engine control module (ECM) learns the airflow through the throttle body to ensure the correct idle. The learned airflow values are stored within the ECM. These values are learned to adjust for production variation and will continuously learn during the life of the vehicle to compensate for reduced airflow due to throttle body coking. Anytime the throttle body airflow rate changes, for example due to cleaning or replacing, the values must be relearned.

An engine that had a heavily coked throttle body that has been cleaned or replaced may take several drive cycles to learn out the coking. To accelerate the process, the scan tool has the ability to reset all learned values back to zero. A new ECM will also have values set to zero.

The idle may be unstable or a DTC may set if the learned values do not match the actual airflow.

Conditions for Running the Idle Learn/Reset Procedure
Scan tool Idle Learn or Idle Learn Reset Procedure
•DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0171, P0172, P0201–P0204, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0300–P0304, P0351–P0354, P0496, P0506, P0507, P0601–P0604, P0606, P062B, P062F, P0630, P0641, P0651, P0697, P06A3, P1101, P1248, P1249, P124A, P124B, P1516, P16F3, P2101, P2119, P2122, P2123, P2127, P2128, P2135, P2138, P2147, P2148, P2150, P2151, P2153, P2154, P2156, P2157, P2176, or P2610 are not set.
•Ignition ON, engine OFF.
•The vehicle speed sensor (VSS) is 0 km/h (0 mph).
Service Bay/On Road Learn Procedure
•DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0171, P0172, P0201–P0204, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0300–P0304, P0351–P0354, P0496, P0506, P0507, P0601–P0604, P0606, P062B, P062F, P0630, P0641, P0651, P0697, P06A3, P1101, P1248, P1249, P124A, P124B, P1516, P16F3, P2101, P2119, P2122, P2123, P2127, P2128, P2135, P2138, P2147, P2148, P2150, P2151, P2153, P2154, P2156, P2157, P2176, or P2610 are not set.
•The engine speed is between 450–4,000 RPM.
•The engine vacuum is greater than 5 kPa.
•The mass air flow (MAF) is greater than 2 g/s.
•The ignition 1 voltage is greater than 10 V.
Reset/Learn Procedure
Scan Tool Idle Learn or Idle Learn Reset Procedure – Performed after the throttle body is cleaned or replaced
 1. Ignition ON, engine OFF, perform the Idle Learn or Idle Learn Reset in Configuration/Reset or Module Setup.
 2. Engine idling, observe the scan tool Throttle Body Idle Airflow Compensation parameter. The Throttle Body Idle Airflow Compensation value should equal 0 % and the engine should be idling at a normal idle speed.
 3. Clear the DTCs and return to the diagnostic that referred you here.
Service Bay/On Road Idle Learn Procedure – Performed after the ECM is programmed or replaced
Note: Do NOT perform this procedure if DTCs are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

 1. Engine idling for 3 minutes.
 2. Observe the scan tool Desired Idle Speed and the actual Engine Speed parameters.
 3. The ECM will start to learn the new idle cells and the Desired Idle Speed should start to decrease.
Ignition OFF for 60 s.
 5. Engine idling for 3 minutes.
 6. After the 3 minute run time the engine speed should return to normal.
Note: During the drive cycle monitor the DTC information with a scan tool to verify DTC P0506 and P0507 do not set. If DTC P0506 and P0507 set, clear the DTCs so the ECM can continue to learn.

⇒ If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.
 7. After the drive cycle, the engine speed should return to normal.
⇒ If the engine idle speed has not been learned, turn OFF the ignition for 60 s and repeat step 6.
 8. Once the engine speed has returned to normal, clear DTCs and return to the diagnostic that referred you here.
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post #5 of 12 (permalink) Old 08-20-2019, 12:05 PM
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DTC P0300-P0306

DTC P0300Engine Misfire Detected


Diagnostic Aids
•A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the following possible sources:
– A tire or wheel that is out of round or out of balance
– Variable thickness brake rotors
– An unbalanced drive shaft
– Certain rough road conditions
– Transmission operation
– A damaged accessory drive component or belt; remove the belt and safely operate the engine to evaluate
•High resistance in the circuits of the injectors may set a misfire DTC without setting an injector DTC. Test the injector circuits of the affected cylinder(s) for a high resistance if you suspect a condition.
•If the condition is intermittent, observing the scan tool IC Circuit Test and Fuel Injector Circuit Test Status parameters may help isolate the condition. The circuit test status parameters will change from OK or Not Run to Fault if a condition exists.
•A condition in the heated O2 sensor (HO2S) heater control circuits may set a DTC P0300.
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post #6 of 12 (permalink) Old 08-22-2019, 08:25 PM
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You could also have a LEAN fuel condition. Find someone with a scanner that shows live data. Take a look at your fuel trims. A positive value will mean it’s adding fuel due to a lean condition.( not sure of the values on an equinox though ) You could have dirty injectors and or a intake leak allowing un metered air into the engine. Try cleaning the Mass air meter with proper cleaner and also checking for loose hose clamps on the air box and throttle body. Hope this helps a tad.
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Last edited by spartus; 08-22-2019 at 08:43 PM.
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post #7 of 12 (permalink) Old 08-23-2019, 11:16 AM Thread Starter
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Thanks, I have a scanner I just have to learn how to use that functionality. Right now I just lookup codes and clear them once fixed.
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2010 Terrain SLE 2.4L I4 FWD Onyx Black
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post #8 of 12 (permalink) Old 08-29-2019, 11:08 AM
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My 2 cents,,,,
What if your GDI engine has LSPI?
Then a gasoline treatment with Techron ( it has PEA) and/or using Shell premium gas ( it has PEA.) ...might help ...
Might help dissolve and remove carbon from inside your cylinders, lodged between cylinder walls and piston rings, and
Might help clean fuel injector for a better spray pattern.

Do not use a "running engine" intake valve cleaner, like CRC to clean intake valves.
..... Root cause might be CARBON on intake valves, breaking off the intake valves, falling into cylinder, and then getting lodged between cylinder wall and piston ... causing LSPI.
If so... only Walnut blasting would address root cause.
My 2 cents. ^^^ who knows??

"Low speed pre-ignition (LSPI) is a premature combustion event, occurring prior to spark ignition
it occurs when engines operate at low speeds and high loads. It can result in extremely high cylinder-pressures and can lead to heavy knock."

An article in "engine builder" says ....
The article titled "Solving Gasoline Direct Injection Issues: The facts and fictions of GDI"
Says...

“You want small droplets of fuel to intertwine with air,” he says.
“What happens with the direct injection engine is you’re squirting that liquid fuel into the cylinder, it gets on the cylinder walls and absorbs into the oil.
What happens during the combustion event is the oil that is on the cylinder walls contains gasoline
so it ignites and it burns off. That’s why a lot of direct injection engines are experiencing significant oil consumption and flash burns in the cylinder.”

An issue known as Low Speed Pre-Ignition (LSPI) typically occurs in vehicles with GDI engines.
Detonation typically occurs ......
.... at the perimeter of the cylinder in the crevice clearance above the top ring between the cylinder and the crown of the piston.

“So when you are at a high load, low speed operation of the engine and depress the throttle slowly it squirts additional fuel through the accelerator pumps
What happens under this low speed, high load situation is
you get bits of carbon and soot that break off from the valves
and ( falls into) the combustion chamber
which makes its way to the cylinder walls where it sticks to the oil and the fuel that’s on the cylinder walls.
When the piston moves up it loads the crevice clearance with carbon,
and those little groupings of carbon and soot get diluted with fuel and oil
which then smolder and act like a glow plug or a wick to cause pre-ignition.”

^^ article in "engine builder" ^^
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Three Equinox with 2.4 engine, 2013, 2016 and 2016
2017 equinox with 3.6 engine with Elite E2 X catchcan
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post #9 of 12 (permalink) Old 09-04-2019, 09:20 AM Thread Starter
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Thanks, I’m half a tank through a bottle of Techron and typically use Shell gas or Costco.

My code just came back today after clearing it Friday when I added the Techron.

Haven’t had a chance to see what my scanner can do yet. I have the Nexpeak NX501. Hopefully this weekend.

Thanks for all the help so far.
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2010 Terrain SLE 2.4L I4 FWD Onyx Black
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post #10 of 12 (permalink) Old 09-04-2019, 06:21 PM Thread Starter
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Just cleaned the mass flow sensor and reset the code. Should know in about 12 starts if that helped at all.

2010 Terrain SLE 2.4L I4 FWD Onyx Black
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