# Check engine light

**URL:** <https://community.cartalk.com/t/check-engine-light/25153>\
**Category:** Maintenance/Repairs\
**Created:** [January 19, 2009, 12:23am UTC](https://community.cartalk.com/t/check-engine-light/25153 "2009-01-19T00:23:46Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![lainey](https://avatars.discourse-cdn.com/v4/letter/l/e95f7d/32.png) [@lainey](https://community.cartalk.com/u/lainey)\
**Post date:** [January 19, 2009, 12:23am UTC](https://community.cartalk.com/t/check-engine-light/25153/1 "2009-01-19T00:23:46Z")

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I have a 2002 Volvo S40 with about 62,000 miles. The check engine light first came on 2 mos. ago and at that time, I changed the gas tank cap, which the Auto Zone Computer said. The light stayed off for about 2 mos. and then back on. Went back to Auto Zone and this time code indicated low cooent, replace sensor or replace thermostat. Coolent was ok and wasn’t overheating and getting adequate heat, etc. As a matter of eminiation I had the sensor replaced. Light stayed off for 1 days and is now back on…any suggestions?

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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:** [January 19, 2009, 12:35am UTC](https://community.cartalk.com/t/check-engine-light/25153/2 "2009-01-19T00:35:59Z")

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How about getting the actual error codes? They should be in the format [P0123]

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**Author:** ![lainey](https://avatars.discourse-cdn.com/v4/letter/l/e95f7d/32.png) [@lainey](https://community.cartalk.com/u/lainey)\
**Post date:** [January 20, 2009, 1:06am UTC](https://community.cartalk.com/t/check-engine-light/25153/3 "2009-01-20T01:06:39Z")

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I think it was P0128

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**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\
**Post date:** [January 20, 2009, 1:15am UTC](https://community.cartalk.com/t/check-engine-light/25153/4 "2009-01-20T01:15:27Z")

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If it was P0128, here is a pretty good discussion of it:

> **[P0128 Coolant Temperature Below Thermostat Regulating Temperature](https://www.obd-codes.com/p0128)**
>
> How to quickly diagnose, repair, and info on symptoms and causes of a P0128 code which generally indicates a failed thermostat.

It would be good to get the actual coolant temp checked (rather than relying on gauge and heat level), and make sure that your cooling fan isn’t stuck on.

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**Author:** ![lainey](https://avatars.discourse-cdn.com/v4/letter/l/e95f7d/32.png) [@lainey](https://community.cartalk.com/u/lainey)\
**Post date:** [January 23, 2009, 4:01am UTC](https://community.cartalk.com/t/check-engine-light/25153/5 "2009-01-23T04:01:59Z")

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Thanks so much for post…I’m having the thermostat replaced next week. We’ll see.