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Old 12-02-2012, 05:46 AM   #1
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Location: Hernando Beach, FL
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Dead speedometer, Christmas tree on the dash

My wife's low-mileage Boxster (138,000+ and holding) developed a group of symptoms at the same time two weeks ago. I should mention that they happen simultaneously and usually after the car has warmed up and been driven 5-10 miles:

The speedometer quits
The odometer quits
No cruise control
The spoiler stays up
The brake fluid and ABS lights light up

After searching this and other forums, I figured that it was a ABS speed sensor, specifically at the left rear; I read that this wheel triggers the ABS computer's speedo/cruise/spoiler functions. So I replaced the LR sensor and still had same problem. Brake fluid is OK, no fuses out and all other systems working well.

My wife has a great attitude and has been using a HUD from her iPhone GPS app, but I'd like to fix this gremlin. It appears the next thing to check is the ABS brake pump, but I'd like to be sure it's bad before throwing another $2-500 at it for a used unit.

Anyone else have this happen?

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Old 12-02-2012, 07:11 AM   #2
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Location: Frederick, MD
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what year? has the ignition switch ever been replaced? have you checked fuses? any water get in the passenger compartment?
"Speed has never killed anyone, suddenly becoming stationary... that's what gets you."
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Old 12-02-2012, 07:49 AM   #3
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It's an '01, non-S. Original ignition switch, fuses are AOK, no water inside. I'll check the ig switch; it's felt a little worn recently (to be expected, considering the miles).
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Old 12-03-2012, 09:01 AM   #4
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My bet is a bad ground. Why, because you have multiple, simultaneous failures that have very little in common except maybe a ground.

If you hunt down the widely distributed & available 986 fworkshop manual PDF, there are pretty good wiring diagrams. One page is devoted to ground points, about 10 total. Find the one(s) possibly related to all your problems, take of the nuts and with a wire brush or what ever get all mating surface shinney.

Put it (them) back together and put some grease (yup) or wd40 on the assembly ( or go to radio shack for there overpriced version of the same). Give a good jiggle and cinch them tight. Might be the fix.

Regards, PK

P.S. Your wife is a trooper.
99 Supercharged 2.5L
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Old 01-20-2013, 02:45 PM   #5
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She's got a speedometer again! Just a follow-up here, with good news. Since last post, I tested the wheel sensors (all ok), changed the ignition switch and had the battery and alternator tested (AOK).

Still the same symptoms, spoiler up, no speedo after first 2-5 miles and abs and brake fluid lights on.

Bought a used abs control unit, installed it with fresh brake fluid and car is back to normal. Well, as normal as a high-mile 986 gets.....which is still better than any regular car!
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Old 03-24-2016, 09:43 AM   #6
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Location: AR
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March 2016 - Any updates or identified causes

I'm having nearly the same issue on my '99 boxster. No water, blown fuses, etc.

In fact, a great independent shop here has replaced the ABS controller x 2 only to have the problem repeat. Alternator and speed sensors both test ok.

Any ideas? We are at a total loss.

Of note, the problem appeared upon engine restart. In other words, it worked fine. Car was turned off, then ABS light and no speedometer (electronic or guage). The rear trunk light comes on at the same time.

The brake light has never come on when this problem occurs; however, I can confirm that the light does function as it does illuminate at test/ignition on.

Many thanks!

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