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AtlGuy

join:2000-10-17
Marietta, GA

Computer Not Ready - GMC Sonoma - Dealer Mechanic Here?

About a month and a half ago, I had a problem with my truck where I had to have a wire replaced due to a short. Approximately 3 weeks after that, I went for my emissions test, and was told my truck was failing because the computer was "not ready."

After looking at my invoice I saw I had already driven around 400 miles, and when asking around found out the computer should've readied itself around 150-200 miles. After driving it another 300 miles and still being told the computer was "not ready," I took the truck to a GMC dealership. It looks like they downloaded a software update, and the service rep I dealt with told me the truck should pass "right now." When I had the truck checked, it failed again. I called the dealership and spoke with another service rep who told me that I still had to drive it about 150 miles.

I drove 200 miles and the truck still failed emissions for the same reason. My battery seemed like it wasn't quite right, and I confirmed that I needed a new one...which I now have in my truck, so from what I understand the readying period starts over, again.

Every emissions test I've had done indicates that Misfire, Components, and Fuel System are Ready.

O2 Sensor, EGR System, Catalyst, Evap. System, and O2 Heater have all shown Not Ready on every test.

I don't live far from my job, so the trips I've taken on my truck have all been short trips. A guy I work with, who used to be a Nissan mechanic, told me that certain sensors won't even begin to ready themselves until you're at a certain speed for a certain amount of time.

He suggested I take it on the interstate for a nice long drive. Is there anyone here that can confirm if what he's telling me is true?

My truck is a 1996 GMC Sonoma, with a 4.3Liter V6, in case that info is needed.

Thanks in advance.



Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
kudos:18

If you short trip the vehicle, then it never fully heats up and it makes the oil and other systems overly contaminated with unburned hydrocarbons plus the sensors can get lazy/covered in soot/carbon. Go road trip it for an hour and blow out the soot.
--
What’s the point of owning a supercar if you can’t scare yourself stupid from time to time?



mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3
reply to AtlGuy

said by AtlGuy:

A guy I work with, who used to be a Nissan mechanic, told me that certain sensors won't even begin to ready themselves until you're at a certain speed for a certain amount of time.

He suggested I take it on the interstate for a nice long drive. Is there anyone here that can confirm if what he's telling me is true?

Yes, he is correct. The "not ready" message is indicative of short trips, and insufficient time to build a data "baseline" for the computer to compare itself against. A long drive including a good amount of "steady throttle" miles should do the trick. Once it is set, you can get the test done and go from there.

-Matt


r81984
Fair and Balanced
Premium
join:2001-11-14
Katy, TX
Reviews:
·row44
reply to AtlGuy

There are certain driving patterns that trigger those tests. If you have access to Alldata you can look them up. (try a local library)
It can take a while for those driving patterns/sequences to happen to trigger the test.
On my sisters Toyota Corolla, it took almost 2 weeks for it to run the gas tank pressure test.

You might want to try searching google for the sequence to trigger the tests.

The dealer should have equipment to force the tests to run if they will not run on their own.
--
»www.ryanoneill.us



AtlGuy

join:2000-10-17
Marietta, GA
reply to mattmag

Thanks everyone for the information. I'm glad my coworker told me what he did, because it was 100% more specific than what I got from the dealer. Needless to say I'm not happy at all with their "service."

mattmag, do you think if I took, lets say, 100 mile drive on the interstate going 70mph or so, that would do the trick, or does the trip need to be longer in your opinion?



r81984
Fair and Balanced
Premium
join:2001-11-14
Katy, TX
Reviews:
·row44
reply to AtlGuy

General Motors Driving Cycle
A complete driving cycle should perform diagnostics on all systems. A complete driving cycle can be done in under fifteen minutes.

To perform an OBDII Driving cycle do the following:

Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.

Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.

Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

»www.obdii.com/drivecycle.html
--
»www.ryanoneill.us



AtlGuy

join:2000-10-17
Marietta, GA

Sweet! Thanks man. I tried searching Google but didn't use the right search criteria apparently. Drive cycle never even entered my mind.

I appreciate that greatly.



Amr8
Pointing out the obvious
Premium
join:2001-12-03
Wichita, KS
reply to AtlGuy

piggybacking on what someone said earlier, when your on the interstate floor the engine a few times and get the RPMs up to break out all that carbon and soot out of the cylinders that might have built up. Do that 3 or 4 times just lay the accelerator down and let it get up and just let go and do that a few more times.
--
Mastering others is strength. Mastering yourself makes you fearless



TheHarvester
Premium
join:2006-08-25
Dana Point, CA
kudos:3
reply to AtlGuy

You don't need to do the drive cycle completely. Where in the hell can you find a location to do it here is So. Cal. If you just take a 40-50 mile round trip on the interstate (as you people over there call it). You should not need ALL the monitors to set but more than likely most of them. We have real good luck telling our customers to drive to a specific location and back. The location is about 20-25 miles from the shop via the freeway (as we people call it over here) and enough of the monitors have set to pass the inspection.



IllIlIlllIll
EliteData
Premium
join:2003-07-06
Hampton Bays, NY
kudos:7

1 edit
reply to AtlGuy

some good advice (as i was told)
to change your engine oil the day before you get it inspected. (if it hasnt been changed)