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Amedee
Amedee, Buick Mechanic
Category: Buick
Satisfied Customers: 21878
Experience:  ASE Master Technician advanced level specialist. Wisconsin certified emissions state inspector
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2003 Buick LeSabre: Mass Air Flow Sensor code..run fine..bank 1 sensor

Resolved Question:

I have a 2003 Buick LeSabre 3.8 4dr It had a Mass Air Flow Sensor code and ran rough. We replaced MAF and seemed to run fine. Customer came back a few days later and simluar symptom with an O2 sensor caode so we replaced O2 sensor bank 1 sensor 1. It seemed to run fine for 20 to 30 miles and then it starts to kick and buck hesitate violently and stalls at stops. Restart engine and will rev to 2500 rpms then it will almost stall the check engine light comes on then goes out. Snap On scanner loses comunication then the engine comes back just like someone shut it off and turned the key back on. It has no codes and now it starts revs up then stalls. It is like the PCM is losing power and restarting. Any ideas of what could be wrong.
Submitted: 3 years ago.
Category: Buick
Expert:  Amedee replied 3 years ago.

Hello!

You might just have a bad ignition switch. This is very common! Check the fuses inside the vehicle to see if they all have battery voltage. If any of them have low voltage, the ignition switch might just be at fault.

Customer: replied 3 years ago.

Checked all fuses and they all have 12 volts. Starts and Stalls unplugged the MAF sensor and the vehicle runs fine plug it back in and the vehicle stalls. We have installed two standard ignition MAF and a GM MAF and vehicle still stalls. Any other ideas?

Expert:  Amedee replied 3 years ago.
Have you checked the voltage going to and coming from the mass air flow sensor?
Customer: replied 3 years ago.
Scanner is reading it but we have not checked it to and from.
Expert:  Amedee replied 3 years ago.
WHen did this problem all start? Was there recent work done to the engine?

Try removing the oil cap with the engine running. See if there is engine vacuum inside the crankcase.
Customer: replied 3 years ago.
It started before we replaced the intake gasket.
Expert:  Amedee replied 3 years ago.
Check the crankcase for engine vacuum and let me know!

Customer: replied 3 years ago.
The tech is gone for the day so he can try it tomorrow.
Expert:  Amedee replied 3 years ago.
Just start the vehicle up and remove the oil cap and see if the engine dies or starts to idle funny.
Customer: replied 3 years ago.
The only way that we can make it run is to have the MAF unplugged can we test it that way?
Expert:  Amedee replied 3 years ago.
Sure.. that would work...
Customer: replied 3 years ago.
We took the oil cap off and it ran fine as soon as we plugged the MAF in it died within 10 seconds.
Expert:  Amedee replied 3 years ago.
Ok.. the next step is to check the engine vacuum at idle and at 2500 rpm in park.

Let me know!
Customer: replied 3 years ago.

The tech is gone do we have to hook a vacuum gage to it, if so we will have to do it tomorrow when he comes in.

Expert:  Amedee replied 3 years ago.
Yes.. you do..

That will be fine...

Talk to you then!
Customer: replied 3 years ago.
Engine vacuum is at 18 to 20 pounds
Expert:  Amedee replied 3 years ago.
Hello!

I take it you are still have the same problem?

Is there still no communication with your scanner?

Do you have power on pin 16 of the diagnostic connector?
Customer: replied 3 years ago.
Yes we are having the same problem. When the car goes to stall the SES light comes on and the scanner looses communication and just before it stalls the engine comes back to power and idles and the scanner recommunicates. It seems to repeat this symptom. Cold start I can drive 20 miles and it runs fine and you shut the car off and then let it cool a few min restart and then wants to stall. Unplug MAF sensor then the engine will run. Can you call us it would be much easier.
Expert:  Amedee replied 3 years ago.
I wish I could... but it is against just answer rules.

If the engine is stalling and you are loosing communication and you do have power on pin 16 of the ALDL connector when the engine stalls, it is going to be a bad ignition switch or a bad module on board your vehicle. SOmetimes one of the modules shorts out and goes bad pulling the other modules off line causing the engine to stall.
Customer: replied 3 years ago.
We have replaced the ignition module
Expert:  Amedee replied 3 years ago.
No.. I am talking about the computers... ABS module, PCM, BCM and so on...
Customer: replied 3 years ago.
This car is a real pain and has no codes, the symptoms are always the same though with a cold start runs good and can drive for 20 miles or so and shut car off, try to restart then stalls. If I rev the engine to2-3,000 rpms it will stay running in a XXXXX XXXXXke condition with black smoke comming out of the exhaust. I h tested all wires from the PCM under hood to every engine control sensor on the car and all checks out ok, trying to eliminate possible shorts or open in wiring.
Expert:  Amedee replied 3 years ago.
When this happens, check the voltage on the fuses inside the vehicle. If they have anything less than battery voltage, the ignition switch is bad and will need to be replaced.
Customer: replied 3 years ago.
So your saying when the start stall symptom is happening to leave the ign. key in run position and test the fuses under the back seat next to the battery for full battery voltage?
Expert:  Amedee replied 3 years ago.
You got it! Check to see how much voltage the fuses have... not if they are good...
Customer: replied 3 years ago.
Ok I'll go and try to get the car to act up and check the volts and get back to you, thanks.
Expert:  Amedee replied 3 years ago.
SOunds good!
Customer: replied 3 years ago.
Just got back from a test drive of approxiamtly 20 miles and it ran good from a cold start. Pulled inside the garage and shut off the car and got out DVOM Meter out and removed rear seat and hooked up meter to a maxi fuse and tried to start. Car 2003 Le Sabre started and stalled repeatedly, left key on and checked volts through all fuses on both post of fuses, and are all 12.7 volts. Tried to start and keep engine running needed to rev 2-3000 rpm's as soon as let off throttle engine dies. Scanned for codes and there were none. When I Kept the engine running after the volts test SES light will come on and the engine will almost die then the Snap-On scanner (Solos) will lose communication then will come back to 2-3000 rpm's and do this repeatedly untill I let off throttle then engine dies as I described earlier. What do you think?
Expert:  Amedee replied 3 years ago.
IT sounds to me like you just have a bad module on board your vehicle. PCM, BCM or even a ABS module.
Customer: replied 3 years ago.
I've been suspecting the PCM myself for a while, I didn't think these newer cars had PCM failure like the older cars as they don't have removable proms in them and have to be burned at the dealership as I'm sure you already know. I had worked on this car for 2-3 weeks off and on in between other cars and my boss said lets take it to the dealer so we did and they couldn't figure it out either. I'm in agreement with you on the possibility of the PCM, without offending you or your tech abilities, how would the BCM or ABS module interfere with the runability of the engine for my own future reference.
Expert:  Amedee replied 3 years ago.
That is a very good question... Have you ever heard of the BUS system? THe BUS system is the circuit that all of the modules talk to each other on. If one of these modules shorts out, it will pull the BUS system down and short out the PCM which will in turn cause your running condition.
Customer: replied 3 years ago.

I've heard mention of it but nothing more. So are you confident in Just replacing the PCM by itself, or will there be further diagnostics needed to confirm this?

Expert:  Amedee replied 3 years ago.
TO be honest with you, when this problem happens, you will need to check ALL powers and ALL grounds going into the PCM to be sure that they check out good. IF that checks out, then you need to get a lab scope on your BUS circuit and see if it is being shorted out. IF it is, then you need to disconnect one module at a time until the problem goes away. IF the BUS system checks out ok along with the powers and grounds going into the PCM, then the PCM is bad and will need to be replaced.
Amedee, Buick Mechanic
Category: Buick
Satisfied Customers: 21878
Experience: ASE Master Technician advanced level specialist. Wisconsin certified emissions state inspector
Amedee and 9 other Buick Specialists are ready to help you
Customer: replied 3 years ago.
Ok, I will check the power and grounds to the PCM tonight and get back with you tomorrow as were almost ready to close here. thanks
Expert:  Amedee replied 3 years ago.
Sounds good!
Customer: replied 3 years ago.
Hi, I checked the PCM's power wires(4) and ground wires (4) specific to PCM only, and they check out good. In fact earlier in my diagnostics I removed and cleaned all grounds from battery to body to engineto make sure there wasn't a ground problem, but made no difference. We do not have a lab scope in our shop to test the BUS circuits, so I belive it will need to go back to a dealership different then the last one.
Customer: replied 3 years ago.
Hi, I checked the PCM's power wires(4) and ground wires (4) specific to PCM only, and they check out good. In fact earlier in my diagnostics I removed and cleaned all grounds from battery to body to engineto make sure there wasn't a ground problem, but made no difference. We do not have a lab scope in our shop to test the BUS circuits, so I belive it will need to go back to a dealership different then the last one.
Expert:  Amedee replied 3 years ago.
Hello!

Sorry for the delay!

Are you saying that all of the powers and grounds check out ok at the PCM?

Are you sure you checked them when this problem was acting up?

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