GM Releases Fix For GMC Sierra Heater Auxiliary Coolant Pump Issue

GM has released a service update for certain units of the 2020 GMC Sierra 1500, 2021 GMC Sierra 1500, and 2022 GMC Sierra 1500 Limited over an issue related to the pickups’ heater auxiliary coolant pump.

The problem: units of the GMC Sierra 1500 affected by this issue are equipped a manual HVAC system (RPO code CP4) and HVAC Control Module (RPO code K33), the latter of which may not activate the auxiliary coolant pump during an engine auto stop event. The pump is required to maintain cabin heater temperature.

The hazards: this particular issue does not pose a safety hazard. That said, it may affect passenger comfort.

The fix: GM technicians are instructed to reprogram the HVAC Control Module with updated software to correct the issue.

Affected components: HVAC Control Module (RPO code K33).

Affected vehicles:

  • 2020 GMC Sierra 1500
  • 2021 GMC Sierra 1500
  • 2022 GMC Sierra 1500 Limited

Number of affected vehicles: it’s unclear how many vehicles are affected by this GM Service Bulletin.

Owners should: GM will notify owners of affected vehicles and advise them to make an appointment with their local dealer in order to correct the issue. Owners who are unsure if their vehicle is affected by this service bulletin can reach out to GM directly with questions or concerns by using the Service Update number and contact information listed below.


  • Service Update number: N222375000
  • GMC Customer Service: 1-800-462-8782

As a reminder, the 2020 GMC Sierra 1500, 2021 GMC Sierra 1500, and 2022 GMC Sierra 1500 Limited were offered with a wide range of powerplant options. Among these is the atmospheric 4.3L V6 LV3 gasoline engine, turbocharged 2.7L I4 L3B gasoline engine, atmospheric 5.3L V8 L82 gasoline engine, atmospheric 5.3L V8 L84 gasoline engine, atmospheric 6.2L V8 L87 gasoline engine, and 3.0L I6 LM2 turbodiesel Duramax engine. Under the skin, the GMC Sierra 1500 rides on the GM T1 platform.

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Jonathan Lopez: Jonathan is an automotive journalist based out of Southern California. He loves anything and everything on four wheels.

View Comments (9)

    • Don't dealerships want you to come in? Although the fixed compensation they get from GM is not exciting they can say "while it's here it's due for an oil change, tire rotation" not covered by warranty.

    • It's a service update, basically a non-safety recall. You get a letter, it shows up if you do a recall search on the GM website, it may or may not expire or be linked to the warranty period, the dealer is supposed to tell you about it when you take your car in, and unrepaired cars may not be sold by the dealer.

      All brands have some type of this. Toyota calls it a Service Campaign, FCA's got Customer Satisfaction Notification, Ford is a Customer Satisfaction Program, etc.

  • stop/start is a nuisance.
    you are not going to save much fuel unless you are doing a lot of stopping with long periods of idling.

  • Why is this only an issue for the Sierra and not the equivalent Silverado? Did I not pay enough when I bought my truck? Is the 10% higher price tag for the Sierra really worth that kind of customer care?

  • Transmission 8L45 & 6L50 experience shutting at about 45mph. I would like to know why GM will not come clean about this problem?