28 May 2018


Sun load sensor:  $40 from the Chevy dealer.
HVAC control module:  $300 from ebay.
Finding out it's apparently a 2¢ fuse:  Priceless.

It was working fine when I left to a friend's house yesterday.

It wasn't working when we got done with lunch.

I am amazed that I didn't scream.

Being car guys we tore The Precious apart in his driveway.  He's paid for the digital version of the service manual and it's 1,000% easier to use than the paper version I have at home.

This is where I discover that there are TWO 10a fuses for the HVAC inside the car, and a 40a fuse under the hood.

Since the 40a runs to the blower motor, and looked fine, we checked the fuses in the car.  They too looked fine.

Check the codes with his Tech 2.  U1000 and U1153.  Those add up to "something on the bus has failed, but the troubleshooting section are all about wiring.

Get out the test light and find that there are two switched leads and one B+ lead going into the HVAC module.

We find that we have a good ground.
We find that we have power at both switched leads that switches like it's supposed.
We find that we don't have power at the B+ lead.

Check fuse again.  Still looks fine.

Install new fuse.

We find we have power at the B+ lead.

Put everything back together and clear codes.

It works fine all the way home.

I'm not completely confident we've fixed it, but I have hope!


  1. Fuses that LOOK good are not fuses that have been TESTED good. I have been bitten by failed fuses that looked good but were open under test more times in a 30+ year career as a tech than I'd care to admit.

  2. Thanks, for sharing the information, it’s very informative post!

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