# GMC Sonoma

**URL:** <https://community.cartalk.com/t/gmc-sonoma/57063>\
**Category:** Maintenance/Repairs\
**Created:** [November 1, 2010, 3:34pm UTC](https://community.cartalk.com/t/gmc-sonoma/57063 "2010-11-01T15:34:23Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![han205](https://avatars.discourse-cdn.com/v4/letter/h/ea666f/32.png) [@han205](https://community.cartalk.com/u/han205)\
**Post date:** [November 1, 2010, 3:34pm UTC](https://community.cartalk.com/t/gmc-sonoma/57063/1 "2010-11-01T15:34:23Z")

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I have a 2001 GMC Sonoma (6 cyl). Heater does not work though the hose is hot near the pump but cold at firewall. I also occasionally hear fluid behind the dash. Did replace thermostat. Do I need to replace heater core or is there a relay/servo that may not be opening to allow coolant to flow? Thanks in advance.

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**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\
**Post date:** [November 1, 2010, 4:44pm UTC](https://community.cartalk.com/t/gmc-sonoma/57063/2 "2010-11-01T16:44:41Z")

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There may be a blockage in the line to the heater core or after it. The core itself may have a blockage in it. I assume that the coolant is at the correct level in the system. To see if the heater core is blocked you could try bypassing the heater with a connection between the ends of the two lines. If the return line is still cool then the trouble is within the supply line.

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**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\
**Post date:** [November 1, 2010, 8:00pm UTC](https://community.cartalk.com/t/gmc-sonoma/57063/3 "2010-11-01T20:00:54Z")

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Cougar: I also occasionally hear fluid behind the dash. sounds to me like the heater core is air blocked. Did you consider that?

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**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\
**Post date:** [November 1, 2010, 9:35pm UTC](https://community.cartalk.com/t/gmc-sonoma/57063/4 "2010-11-01T21:35:27Z")

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Yes I did JEM and was one reason I mentioned the coolant level. I suppose there could be an air bubble in the heater core.