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Old 01-12-2018, 08:40 AM
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Default Clicking sound from under drivers side of dash

Thanks for any help in advance.
I have a 2000 Blazer 2wd, 2dr, automatic, 121,000 miles, 4.3 v6 still running good.
Most everything on Blazer still working or fixed so far. Problem I cannot figure out is a few weeks ago I noticed the cruise control does not engage, and when I accelerate from a stop around the 15 - 25 miles per hour range (normal driving) there is a clicking sound like a relay clicking on and off 3 or 4 times rapidly under the drivers side of the dash? I have checked all the internal and under hood fuses, all OK. All this started since the winter weather started here in Illinois?
Anyone have any ideas what to look for?
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Old 01-15-2018, 10:24 PM
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Short answer: I think your cruise control module, the box the cruise control throttle cable goes into that is mounted on the engine compartment firewall, is bad.

Long answer: I've had the cruise control module go out on me that is mounted on the engine compartment firewall but I cannot remember if I also noticed a clicking sound from under the dash when it was bad.

Also, there is what is called the Body Relay Block located under the driver's side dash, above the parking brake pedal. It has relays on it that control multiple circuits, including the cruise control.

A couple possibilities are that the cruise-control hardware is bad and what you are hearing is a good relay trying to activate a bad circuit in the module OR you are hearing a bad relay not working correctly while trying to active functioning cruise-control module.

I've attached scanned pages from my 1999 GM manual for reference. There are a couple references to the cruise-control system. According to a schematic I have, the B2 connection also is used to get/give information from engine controls electronics (throttle?) when the vehicle has an automatic transmission. (For manual transmissions it uses instead a circuit with a clutch pedal switch.)

Also, my manual makes reference to a "low-speed lockout" circuit in the cruise control module itself that that prevents the cruise control engagement below about 25 mph.

It would seem that the low-speed lockout circuit is causing a relay on the Body Relay Block to engage/disengage as you accelerate or decelerate through 25 mph.

My guess is that your cruise control module is bad and the relay you are hearing is good. Living in the engine compartment, the cruise control module lives in a nasty environment; extreme temperature swings, moisture, salt, all very bad for circuitry.

If you figure it out, let us know.

Good Luck
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