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#1
12-07-2004, 07:08 PM
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service engine soon light
why does my service engine soon light come on when i go over 65mph on the freeway? this is the only time it comes on. everything seems to be fine. does anyone have any ideas?
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#2
12-07-2004, 08:13 PM
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Re: service engine soon light
My 96 sierra used to do the same thing , only come on when on the highway......turned ouyt to be a bad O2 sensor
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**2007 Avalanche LT. **  6" Pro Comp lift 305/55/20 BFG A/T KO'S K&N FIPK GENII Flo Pro V force muffler & 4" slash cut stainless tips Color matched front and rear Bowties 3" polished stainless bull bar and Nerf bars
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#3
12-07-2004, 09:42 PM
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well my o2 sensor is brand new... any other i ideas?
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#4
12-07-2004, 09:50 PM
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Re: service engine soon light
Quote:
Sometimes a loose gas cap will make that light come on.
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1996 K2500 Reg Cab Long Box 5.7 Vortec, HD 5-speed manual (NV4500) LT265/75R16E Toyo Open Country M/T Hypertech Power Programming (AWESOME) K&N Air Filter, Flowmaster Exhaust Centerforce Dual Friction Clutch Pioneer Head Unit, MTX 200 Watt Amp, MTX 10" Thunder 4500 sub "To be old and wise you must first be young and stupid"   
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#5
12-08-2004, 08:16 PM
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Re: service engine soon light
What year is your truck. My 88 had 1 O2 sensor, my 96 had 3 and my 2000 has 4.
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**2007 Avalanche LT. ** 6" Pro Comp lift 305/55/20 BFG A/T KO'S K&N FIPK GENII Flo Pro V force muffler & 4" slash cut stainless tips Color matched front and rear Bowties 3" polished stainless bull bar and Nerf bars
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#6
12-09-2004, 06:54 PM
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mine is a 90 and i think it only has one o2 sensor... the light stays on until i turn it off for a sec and when i turn it back on its off....
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#8
12-10-2004, 10:50 PM
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im going to assume that everything that has to do with smog is in good working order because i just had to fix it to pass... wich it did with flying colors.
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#10
12-14-2004, 11:43 AM
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Re: service engine soon light
my 88 had the same problem and it ONLY showed up when I drove over 55mph. It turned out to be the Vehicle speed sensor. I don't know why this did the trick, but i realized that it only did it after I changed the tranny. It still worked but it wasn't quite right.
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Matthew Brough  1997 Geo Prizm -- 301,000 miles 2000 Honda Accord -- 225,000 miles 2004 GMC Yukon XL -- 223,000 miles 1987 Jeep Comanche -- 116,000 miles 
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#11
12-14-2004, 12:08 PM
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Re: service engine soon light
How about you pull the code..this will give you a wealth of information.
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Why do you never have enough time or money to do the job right the first time, but enough time and money to do it again? Got all the certifications 25 years ASE Certified Master Technician GM WCT Yea..I work at a DEALERSHIP....got a problem with that? Want to diagnose cars like the Pros? FOR SALE: OTC Perception 2 channel Labscope (badged as a Matco Reality) This is my personal labscope that I use to diagnose waveforms, like new, comes with leads and training video PM Me for details
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#12
12-14-2004, 02:35 PM
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ok. where is the speed sensor? and how many do i have? and what do you mean by pulling the code? how do i do that
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#13
12-14-2004, 11:27 PM
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On a 1990? You take a little piece of wire (about 2-3 inches) strip ends, bend in a U, and jumper the dianostic terminal. turn ign. to ON, CES lite will flash 12 three times (I think) thats the "handshake" or system ready code, then it will start giving trouble codes in morse code (three times for each bad code) then it will finish with the same #12 three times. Example 12,12,12 32,32,32 12,12,12 that would be one trouble code #32 you look up 32 and see EGR malfunction...etc. It's been awhile since I had a OBD 1 ,so someone back me up please.
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