Intermittent no start condition

MLBC 1216

MEMBER
2008 CHEVROLET IMPALA
6 CYL
4WD
AUTOMATIC
180,000 MILES

Battery died put in new one. Three or four days later wouldn't start, let set for some time, then it started. Took it back to where I got battery they checked it out, battery fine. Showed I needed a new alternator, put that in few days later no start again. Took it into the garage two different times their diagnostic won't show nothing unless it won't start while it is hooked up, left it with them three days first time and four days the second time and it never failed to start thank goodness they didn't charge me. I'm at my wits end. I never know when it is going to act up. Everything else works it just won't crank. Does the computer have to be reset after changing the battery? According to owners manual if the battery goes completely dead it does. Help I'm about to blow the whole thing up. Thank all help will be appreciated.

5 Replies

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello,

This could be a problem with your vehicle's Crankshaft Position Sensor (CKP) starting to fail. Before I go on, I understand how frustrating intermittent problems can be to track down. With a little patience, we will get it tracked down so you can get it fixed. Okay, your vehicle's Power-train Control Module (PCM) or "computer" uses the signal from the CKP to determine the rotational speed of the crankshaft for rpm's and misfire monitoring. If it does not get a signal from the CKP it will not know that engine is rotating and will not send signals to the coils and fuel injectors to turn on to start your engine. Unfortunately, in order to test the CKP you need an oscilloscope to check the wave forms, but the good news is they are relatively inexpensive. You can pick a decent one up on Ebay or Amazon for $15.00 to $20.00. I have included a few links below for you to go to:

https://www.2carpros.com/articles/how-a-crank-shaft-angle-sensor-works
https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor
https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

I have also included in the diagrams down below a diagram of the location for the CKP for three different engine options for your vehicle because I was unsure of your vehicle's engine size as well as a factory description of what your vehicle's CKP does. Please go through this information and get back to us with what you find out. If this is not the problem, we have other options available to track the problem down.

Thanks,
Alex
2CarPros

Images (Click to make bigger)

SPONSORED LINKS

Was this

answer

helpful?

Yes

No

+1

Saturday, March 6th, 2021 AT 12:32 PM

MLBC 1216

MEMBER
3 POSTS

Hi Alex. Thanks for answering me back, I have never had any trouble with it stopping while moving or idling just starting this all started last November 2018 when I had a dead battery replaced. Had a couple days wouldn't start, took it back checked battery was fine, needed starter got one. Couple days no start back again, needed alternator, couple days again no start back again. Nothing showed up. Took it to an electronics place they had it for several days couldn't get it to do anything bring it home and sure enough it starts doing it again. It does this anywhere from once to twice a week, drive it somewhere park it, come back try to start absolutely nothing no clicks or anything yet the lights work radio etc. Let it set anywhere to ten minutes to half an hour or more she will start. I'm no mechanic so what you tell me to do I'll have to relay to a mechanic here in DesMoines Iowa. Happen to know of a good one? I'm not very happy with all the ones I've had so far. Thank you for your help it is very much appreciated. Marie

Was this

answer

helpful?

Yes

No

Saturday, March 6th, 2021 AT 12:32 PM

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello again,

Okay, don't worry. With a little patience we will get it figured out. Okay, let's get on the same page so we know exactly what we are working on. Could you please give me the exact engine size of your vehicle. This will help me tremendously because your year, make, and model of vehicle has three different engine options available.

Thanks,
Alex
2CarPros

Was this

answer

helpful?

Yes

No

Saturday, March 6th, 2021 AT 12:32 PM

MLBC 1216

MEMBER
3 POSTS

Hi Alex, it's me again. I couldn't get things to match up on my manual so I got this off the emissions sticker on the motor. It has a 3.5L V6 engine. The car is a 2008 Impala LT, and if you need it the 8th character of my VIN number is N. It didn't even dawn on me to send it before. I know better too, because that is the first thing they ask at the garage. Anyway, thanks again. Marie

Was this

answer

helpful?

Yes

No

Saturday, March 6th, 2021 AT 12:32 PM

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello again, That is what I need. Thank you. So, let's start with some basic stuff. Sometimes it's this easy. 75% of all electrical problems on a vehicle's electrical circuits is due to poor grounds. I am going to have you check the ground for the control side of the starter relay. The starter relay is located in the under-hood fuse block, but the ground that we want to check is ground #111. It is located on the transmission to engine bolt above the starter. I have included your vehicle's starting circuit wiring diagram and ground #111 location description and diagram in the diagrams down below. Everything we are checking will be hi lighted for you. When we check this ground make sure that it is clean, corrosion free, tight, and making good metal to metal contact. A relay is nothing more than an electro mechanical switch, much like a light switch in your home. It has two sides to it, a control side and a power side. The control side will be like your arm which you use to turn the light switch on in your home. In the relay though power is supplied by the Engine Control Module (ECM) and energizes a n electromagnetic coil. When the coil is energized it affects the other side of the relay, the power side. This side is like the actual light switch in your home. It has battery voltage going to it and it continues on to your vehicle's starter, but the switch is left open all of the time, except when the electromagnetic coil from the control side of the relay is energized then it pulls the switch closed, allowing the battery voltage to reach your vehicle's starter, making it work. The ground we are checking is the ground wire coming from the electromagnetic coil. If this is bad, the electromagnetic coil can't energize, the switch can't close, and the battery voltage can't reach the starter, and it will not work. If it is loose or has unwanted resistance, i.E. Corrosion, it could work intermittently. Please get back to us with what you find out. If it's okay, we will continue from there.

Thanks,
Alex
2CarPros

Images (Click to make bigger)