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Vehicle starts and immediately stalls intermittently

Tiny
AL514
  • MECHANIC
  • 2001 CHEVROLET IMPALA
  • 3.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 144,000 MILES
Vehicle starts and immediately stalls intermittently, of course this is the same Impala I have been having all kinds of problems with, one after the other. *No check engine light. I am going to go through the motions of regular checks (fuel pressure, sensor checks, scans etc). This car has a dual hall effect crank sensor (3x and 18x). The book reads that the lose of either of these signals will prevent the car from restarting at all. It also has a camshaft position sensor that controls SFI. The cam sensor signal can be lost and the vehicle will be able to be restarted and run in Limp in mode. I think I am dealing with a fuel pressure issue although I have not got to this test yet (i am getting there). My question is, I pulled the vacuum line off the fuel pressure regulator and had no change in engine performance, even with throttle snap test. Just wondering if I should chase the cam sensor next if my fuel pressure tests come out okay (considering I have a no code condition)? This stalling issue will happen cold or hot and car will start right back up and run fine. But the stalling is happening more often now but only on start up. Changing the crank sensor on these is a lot of work considering it is behind the harmonic balancer. Any tips my friends?
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Friday, September 23rd, 2016 AT 8:08 AM

29 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
Just remember, any testing you do has to be done while the problem is present.

Are you sure you do not have any security indicators when this happens?
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
AL514
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No, I have not had any security lights on. The problem is getting worse, so I do not suspect any security systems causing this.
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
Those are the exact symptoms of Passlock activation.
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
AL514
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I have not had any of these problems before, should I pull the security fuse here or whats my next check for pass-lock, I am not trained on Chevrolet's security systems.
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
WRENCHTECH
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The first thing is look for the indicator which may be a very small LED flashing. Diagnosing the system will require a professional, bidirectional scan tool.
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
AL514
  • MECHANIC
  • 4,118 POSTS
I guess anything is possible at this point. I am finding this car has been hacked, there are cut wires and an ACC module tie rapped up under the dash. Someone has made a mess under here =/. Im assuming like a lot of other cars this security system runs through the radio or such? Looking like a nightmare so far.
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
AL514
  • MECHANIC
  • 4,118 POSTS
Can I bypass this system some how? It is a real mess under the dash.
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
WRENCHTECH
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I am sorry no you cant.
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-1
Friday, March 12th, 2021 AT 9:24 AM
Tiny
AL514
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Okay, so there is a way to turn the PASSLOCK system off through the Radio settings, I have no light on my dash for any locking or security system being on.
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
AL514
  • MECHANIC
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And also I thought the PASS LOCK system caused a no crank situation?
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
WRENCHTECH
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You cannot shut off Passlock and a Passlock failure will cause an immediate start and stall.
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Friday, March 12th, 2021 AT 9:24 AM
Tiny
AL514
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Is Passlock light same light as change engine oil light on dash? Or different light all together? You mention small blinking LED?
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Friday, March 12th, 2021 AT 9:25 AM
Tiny
AL514
  • MECHANIC
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Pass-lock is part of ignition switch correct? Can I just replace the switch if this is the problem? These GM's are starting to be a real pain lately. I am having to replace parts every month now after 140,000 miles.
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Friday, March 12th, 2021 AT 9:25 AM
Tiny
WRENCHTECH
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The ignition switch may or may not be the problem. A new switch will have to be programmed after installation.
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Friday, March 12th, 2021 AT 9:25 AM
Tiny
AL514
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I have not installed any new parts yet, and every other part I have installed was bad, ie MAF etc. I just have not dealt with this pass-lock system as of yet.
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Friday, March 12th, 2021 AT 9:25 AM
Tiny
WRENCHTECH
  • MECHANIC
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There are many independent shops that have the equipment and it costs considerably more than $2,000.00. The diagnostic charge would probably be a lot less than what guessing would cost.
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Friday, March 12th, 2021 AT 9:25 AM
Tiny
AL514
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I'm trying to learn whats involved with the passlock, is there more than just the BCM and ignition switch?
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Friday, March 12th, 2021 AT 9:25 AM
Tiny
WRENCHTECH
  • MECHANIC
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The theft deterrent system has been incorporated into the Body Control Module (BCM). The theft deterrent system prevents the vehicle operation if the correct key is not used in order to start the vehicle. The ignition key turns the ignition lock cylinder. The cylinder rotation produces an analog voltage code in the PASSLOCK sensor. This voltage code is received by the BCM. The BCM compares the voltage code to the previously learned voltage code. If the codes match, a class 2 message is sent from the BCM to the Powertrain Control Module (PCM). The message enables the fuel injectors and the crank relay.

The design of the PASSLOCK system is to prevent vehicle theft by disabling the engine unless the ignition lock cylinder rotates properly by engaging the correct ignition key. The system is similar in concept to the passkey system. However, the PASSLOCK system eliminates the need for a key mounted resistor pellet.

The components of the PASSLOCK system are as follows:

The ignition lock cylinder
The ignition switch
The PASSLOCK sensor
The body control module (BCM)
The SECURITY indicator
The powertrain control module (PCM)
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Friday, March 12th, 2021 AT 9:25 AM
Tiny
WRENCHTECH
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The Passlock system may not even be your problem. You should be checking your fuel pressure with a gauge also.
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Friday, March 12th, 2021 AT 9:25 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,940 POSTS
Hi Al,

Yes I would hang a fuel pressure gauge on there and check if you have spark while the engine is not running.

Here is a couple guides that will help you. please get back yo us with the results.

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

and

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Best, Ken
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Friday, March 12th, 2021 AT 9:25 AM

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