Mystery Check Engine Light

[Andrew Selinger]

I have 2021 AT4 with the 6.2L, just recently a check engine light has come on and am a bit stumped on it.  I have read the codes on the ODB11 and the reader I have shows a P2CB9 code but it give me an "information unknown" reading.  My GMC app however tells me that nothing is wrong and all systems are normal.

 

I search online and find that the P2CB9 code is a "cooling fan 2 underspeed" however I live in Canada, its -25 degrees Celsius outside and there should be no reason that cooling fan 2 needs to run, or if I need to get it to run, its too cold out to try and get it to engage.

 

Would taking the negative battery post off reset this code?  its not like its immediately urgent in my life to get it to the dealership due to im not worried about it overheating, but its blocking my command start from working and its pissing me off because its cold outside.

 

Am I chasing the right rabbit?

 

Thanks in advance

[Transient]

This may be horrible advice, but have you tried disconnecting the battery for 10 minutes or more to clear the code and see if it comes back on later on down the road?  In Transient's world of figuring things out, step 1 is to figure out if you really have a problem.  If it comes back you have a problem.  If it doesn't, you had an electrical gremlin.  It's probably horrible advice, but it has worked for me.

[Andrew Selinger]

19 minutes ago, Transient said:

This may be horrible advice, but have you tried disconnecting the battery for 10 minutes or more to clear the code and see if it comes back on later on down the road?  In Transient's world of figuring things out, step 1 is to figure out if you really have a problem.  If it comes back you have a problem.  If it doesn't, you had an electrical gremlin.  It's probably horrible advice, but it has worked for me.

I dont think this is horrible advice at all.  I guess I am just making sure that pulling the battery would fix this issue.  I'll give it a try, the unit is currently in the garage defrosting.

[Transient]

2 hours ago, Andrew Selinger said:

I dont think this is horrible advice at all.  I guess I am just making sure that pulling the battery would fix this issue.  I'll give it a try, the unit is currently in the garage defrosting.

I honestly don't know if it would fix the problem.  You'll find out if you try it.  There are other more credible people on this subject than I.  Hopefully they'll chime in soon. 

[Gangly]

P2CB9 - Cooling Fan 2 Underspeed Performance

 

There was a bulletin somewhere within GM saying that some vehicles will randomly show this code and there is no clear reason why yet, but its not something to worry about.  

 

Basically, it doesn't appear like its anything to worry about unless you get it repeatedly.  Disconnect the batter, let it sit for 10 minutes, then reconnect it.  

 

Involved Region or Country North America

Condition:  If the customer did not bring their vehicle in for this concern, DO NOT proceed with this.

 

Some customers may comment on the Service Engine Soon Lamp Illuminated. Technicians may find one or more of the following DTCs set.

– P0494 - Engine Cooling Fan Speed Too Low

– P2CB9 - Cooling Fan 2 Underspeed Performance

– U0632 - Lost Communication with Engine Cooling Fan

– U0633 - Lost Communication with Engine Cooling Fan 2

 

Cause: GM Engineering is attempting to determine the root cause of the above condition. Engineering has a need to gather information on vehicles PRIOR to repair that may exhibit this condition. As a result, this information will be used to "root cause" the customer's concern and develop/validate a field fix.

Edited February 7, 2022 by Gangly