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99 BMW Z3 2.8, Coil-overs, PowerStop Brakes, 7.5inX16 Alloy Rims, & Personal Enhancements
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Discussion Starter · #1 ·
On a recent road trip this week, I had an issue with the cruise control cutting out on its own or not engaging at all. It seemed to be random. I had about a 3hr drive and it worked perfect at first, but when I went to engage it half way thru my trip, it would not. On the way home it was working as needed and then would cut off on its own. It would reactivate a couple minutes later when I'd try, but then drop off randomly later. Any specific areas to start checking? Is this common? Thanx in advance for your help.
 

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It sounds like a faulty brake switch that cancels the cruise when the brakes are applied. When it wont engage, try putting your left foot under the pedal and lifting slightly and try engaging again. Will sometimes help the switch make contact again.
 

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24 years professionally and counting. Blacklane is also correct. I just typically go straight to the brake switch first since there are many automatics. Not much else will usually cause an erratic, intermittent cruise operation typically.
My manual '98 cruise hasn't worked at all. Check fuses first? Brake/clutch switches? I have only basic tools. Also, bending, crouching, and twisting don't come so easy anymore, so I tend to leave the non-trivial stuff to my mechanic.
 

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My manual '98 cruise hasn't worked at all. Check fuses first? Brake/clutch switches? I have only basic tools. Also, bending, crouching, and twisting don't come so easy anymore, so I tend to leave the non-trivial stuff to my mechanic.
Sounds like the best place to start. Not sure if the 98 has electronic throttle control or not? If not, there might also be a cruise relay you might try to swap with another like relay. If so, try to pick something not running related: horn - fog lights - etc. Most cruise units give very few problems. Usually an input failure. On ETC systems, cruise is controlled by the PCM which controls the throttle body, the same as it does the throttle as there is no cable. No wiring diagrams in front of me so just going off common thoughts.

PS: Wifesauto - I started as solo mechanic for a wrecker service with over 20 trucks at the time. Went to cars due to the nasty diesel oil and weight of parts. Everything easier to get to, just weighed a ton. Also did tank hydraulics and electronics in the Army prior (45K). Later, owned a Snap On Franchise for 7 years. Wish I would have opened a shop instead. Just didn't want to deal with employees.
 

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99 BMW Z3 2.8, Coil-overs, PowerStop Brakes, 7.5inX16 Alloy Rims, & Personal Enhancements
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288 Posts
Discussion Starter · #9 ·
Thanx everyone for the input. I'll "twist" myself under the dash and check out the switches. Thanx again.
 

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Another place to look would be the wiring harness that goes into the trunk lid.

Broken or chafed wires here will cause all kinds of strange and unusual electrical gremlins, including cruise control failure, gas guage flakiness, and dash light malfunctions.

Its a high stressed area due to the trunk opening and closing.
 
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