Main computer location

Tiny
MAZURREXAM@GMAIL.COM
  • MEMBER
  • 2007 BUICK LUCERNE
  • 3.8L
  • 6 CYL
  • AUTOMATIC
  • 56,000 MILES
I need to change it but the dealer will not say where it is.
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Saturday, June 9th, 2018 AT 6:47 PM

9 Replies

Tiny
CARADIODOC
  • EXPERT
There are two possible reasons for this. First, unless you spoke with a mechanic who is familiar with this model, ninety five percent of the people at a dealership do not know where specific parts are located. This includes service writers you speak with at the desk. If you did speak with a mechanic he knows that unless someone actually diagnosed the computer as being defective, it is the last thing on a long list of suspects for a no-start condition you listed in your other post. He might think he is preventing you from wasting your money on an expensive part that needs to be programmed by them to your vehicle, and it likely will not solve the problem.

Also, be aware that "will not start" tells us as much as phoning your doctor and telling him, "I am in pain". He will not know if you have a hang nail, a stomach ache, you cut your foot off with a chainsaw, or your ex-girlfriend came back! You need to list the exact symptoms including whether or not the starter spins the engine and at the proper speed, if you only hear a light click, a single, rather loud clunk from the starter, or nothing at all. What happens to the brightness of the interior lights or head lights when you try to start the engine. We need a lot of observations and clues to figure out where to send you first and what to test.

Your Engine Computer is listed as being "front left side of the engine compartment, inside the air filter housing. I found this drawing that shows its location. In case it is hard to read, I put a nifty red circle around Item number 2.
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Saturday, June 9th, 2018 AT 9:22 PM
Tiny
MAZURREXAM@GMAIL.COM
  • MEMBER
  • 2007 BUICK LUCERNE
  • 3.8L
  • 6 CYL
  • AUTOMATIC
  • 56,000 MILES
Will not start.
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Sunday, June 10th, 2018 AT 12:08 PM (Merged)
Tiny
ASEMASTER6371
  • EXPERT
Good morning.

You need spark, fuel and compression to run.

Have you checked any of these items?

Does the battery crank the engine over?

We need as much information as you can provide.

Roy

https://www.2carpros.com/articles/car-battery-load-test

https://www.2carpros.com/articles/car-cranks-but-wont-start

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-test-an-ignition-system
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Sunday, June 10th, 2018 AT 12:08 PM (Merged)
Tiny
MAZURREXAM@GMAIL.COM
  • MEMBER
Thanks, I just needed to no where the main computer is located?
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Sunday, June 10th, 2018 AT 12:08 PM (Merged)
Tiny
MAZURREXAM@GMAIL.COM
  • MEMBER
The car starts and runs for two minutes then shuts off.
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Sunday, June 10th, 2018 AT 12:33 PM
Tiny
MAZURREXAM@GMAIL.COM
  • MEMBER
I found the computer then I put on plastic gloves to handle it checked the wires they were in good shape opened it up no green corrosion, but I still cleaned it with electrical cleaner placed it back in and started it and it still starts for a minute then it shuts off. So I do not know should I buy a computer and then what do they have to reset it at the dealer or what should I do? Thanks Steve.
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Sunday, June 10th, 2018 AT 6:29 PM
Tiny
CARADIODOC
  • EXPERT
You are still fixated on the computer, but that should be your last suspect after all other potential causes have been eliminated. You need to start by determining what goes missing when the stalling occurs. As ASEMASTER6371 said, you need spark, fuel, compression, and correct timing for the engine to run. Compression and timing will not be intermittent, but loss of spark and fuel commonly are. In fact, loss of spark causes perhaps three percent of stalling and crank/no-start problems. Loss of fuel pressure causes maybe another two percent of those problems. Loss of spark and fuel pressure is responsible for a good ninety five percent of stalling problems.

A good suspect on all car brands other than Chrysler products is the mass air flow sensor. They do not cause as many problems as they did back in the late 1980's and early 1990's, but sometimes if you tap on them while the engine is running, that will cause the stalling to occur. Same with the Engine Computer. If it has broken solder connections inside, tapping lightly on it can cause the problem to occur.

Another cause of stalling I read about quite often is corroded ground connections, particularly inside the car. They are tight and secure, but unbolting them and shining up the terminals seems to cure a number of issues.

If you connect a fuel pressure gauge to the fuel rail and find pressure drops when the stalling occurs, and you still have spark, suspect the fuel pump or the strainer attached to the pump's housing. Chrysler fuel pumps almost always fail by failing to start up, leaving you sitting in the driveway. Once running, they rarely stop running while you are driving. GM pumps are just the opposite. They almost always start up, then fail later while you are driving, leaving you sitting on the side of the road. To my knowledge, time is not a good symptom in diagnosing a bad fuel pump, meaning it will fail after ten minutes one time and maybe it takes twenty five minutes to fail the next time. Therei s no regular pattern like you observed.

A real big cause of stalling on all car brands is the crankshaft position sensor or camshaft position sensor, and those commonly fail by becoming heat-sensitive, then they work again after cooling down for about an hour. The typical symptoms are the engine runs fine as long as you are driving and natural air flow keeps those sensors cool, then, once you stop for a short time, as in when filling with gas, heat from the engine has time to migrate up to the sensors, causing one to fail. On most cars, a failed sensor will result in no spark, no injector pulses, and no fuel pressure. Fuel pressure can be misleading because the pump will still run for one second when you turn on the ignition switch. That keeps the pressure up, but it will not resume running when you are cranking the engine.

The first thing you should have done was to have the diagnostic fault codes read and recorded. A code can be set related to one of those failed sensors, but by disconnecting the Engine Computer, that valuable data was lost. Disconnecting the battery in a misguided attempt at resetting something is another way people loose this information. Very often a fault code for a failed sensor will not set again just from cranking the engine. They need more time to set, as in when a stalled engine is coasting to a stop. At this point, I would find a code reader to see if any fault codes have set, but if there is none related to those two sensors, that is not conclusive the sensors are not failing when one gets hot.

The next thing is to connect a scanner to view live data. The two sensors will be listed under the "Inputs/Outputs" menu with some way to show if their signals are showing up at the Engine Computer. They will both be listed as missing once the engine has stopped rotating, so you have to watch if one switches to missing just before the engine stalls, or if it is listed as missing while cranking the engine.

The scanner also has a test mode that allows you to command the Engine Computer to fire ignition coils and injectors, and turn on the fuel pump. If one of those does not respond appropriately, you have to decide if the circuit needs to be diagnosed or if it is being caused by the computer.

If you do need to replace the Engine Computer, the engineers at GM have designed in a number of tricks to separate you from your money after the sale. One of those is requiring you to buy a new computer from one of their dealers, and having them program it to your vehicle's ID number. They sure do not do that for free. That can be done by independent shops for many other car brands, but from all the complaints I hear from GM owners, it is likely you will need to visit the dealer for that. Of course they will not want to reprogram a computer you found at a salvage yard, and in fact, there are some computers that can only be reprogrammed to different vehicles three times before that no longer works. That prevents mechanics from having used computers on hand to try on multiple vehicles as tests.
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Sunday, June 10th, 2018 AT 8:28 PM
Tiny
MAZURREXAM@GMAIL.COM
  • MEMBER
Thank you, Steve.
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Monday, June 11th, 2018 AT 5:36 PM
Tiny
KEN
  • ADMIN
Did you find the location of the PCM? There is a diagram in the first reply post did you see it?
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Thursday, June 14th, 2018 AT 10:51 AM

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