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Category: Chevy
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Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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2004 Impala: intermitent..Good battery and new starter and crank relay

Customer Question

Please help with 2004 Impala 3.8 intermitent no start. Good battery and new starter and crank relay. I am an old school mechanic out of the trade for 24 years but still try and do what I can. This has been going on for a month now. Car may start 30 times no problem and then does not crank. Then starts after a short wait (20 - 30 minutes).
First time it happened I pulled the relay out marked crank relay and banged it a few times, put it back and it started so I replaced it. A week later same thing.
Next time it happened I banged the starter with a hammer and it started so I replaced the starter. Went on a 1,000 mile trip with no problems. Got home and same thing. This time waited 10 minutes and it started.
I have also noticed the security light comming on from time to time and it has been only since the intermittent no start has been occurring.
Today I thought I would get old school smart and put a jumper button under the hood to activate starter solenoid from jumper button if it happened again. When I tried it it cranked but when I turned the key to on and jumped the starter it cranked but did not start. Security light came on so obviously the security circuit disabled fuel supply. I pulled the jumper button out and again had a no start condition from key. I rebooted the battery and still no start. I finally but the car in neutral, rolled back a few feet, put it in park and it started.

What do you think is going on. What is left? Neutral switch, ignition switch or security system malfunction???? Can the security system be disabled? No body would want to steel this P.O.S. anyay. Please help.

Tom Fitsell [email protected]
Submitted: 6 years ago.
Category: Chevy
Expert:  AMEDEE replied 6 years ago.
Hello and Welcome to Just Answer. My name is XXXXX XXXXX I will try my best to assist you and your 100% satisfaction is my goal. I have been working on these vehicles for over 10 years so I am very familiar with this system and how they work. However, keep in mind, that I need some solid concrete facts/evidence/clues from you in order to give you a good answer about your vehicle. Please realize that all my answers are based solely on the info that you provide me with.

Chances are you just have a bad pass lock sensor inside the ignition switch. This sensor inside the ignition switch receives a reference voltage from the BCM when turning the key on. This means that the sensor inside the ignition switch is considered to be a hall affect sensor. When turning the key on, the pass lock sensor receives 5 volts from the BCM. IT will then send a voltage reading back to the BCM after it goes through the resistor. The voltage going back to the BCM will be considerably lower than 5 volts because it went through the resistor thus lowering the voltage. The BCM "learns" this reading over time. The voltage reading coming back into the BCM needs to be the same every time the key is turned on. If not, then this is what causes the no start condition. Sometimes the BCM will "forget" this value or sometimes the ignition switch will start to go bad and will not send out the same voltage reading each time the key is turned on thus resulting in this no start condition. That is when a relearn procedure usually does the trick. If not, the ignition switch usually needs to be replaced.

Here is the relearn procedure.

Turn ON the ignition, with the engine OFF.

Attempt to start the engine, then release the key to ON, vehicle will not start.
Observe the SECURITY telltale. After approximately 10 minutes , the telltale will turn OFF. The vehicle is now ready to relearn the Pass lock Sensor Data Code and/or password XXXXX the next ignition switch transition from OFF to CRANK.
Turn OFF the ignition, and wait 5 seconds .
Start the engine, the vehicle has now learned the password.
AMEDEE and 3 other Chevy Specialists are ready to help you
Customer: replied 6 years ago.
I am glad you e-mailed back. I lost the page while I was clicking around and was not able to accept answer. You got me on the right track. I did the re-learn process but it happened again so I guess I need an ignition switch. Reading about this problem on the net many people are re-experiencing same problem after replacing ignition switch. Is there a way to by pass pass-lock security system?
Expert:  AMEDEE replied 6 years ago.

Thanks for the accept!

Unfortunately, no.. there is no way to by pass this security system. You will need to replace the ignition switch if you are are planning on fixing this problem the correct way.