GMC Sierra: Intermittent Starting Problem. Diagnosing and Solving the Issue

Permanent faults can be very annoying, but as soon as the issue becomes intermittent, making it even more difficult to diagnose, things become quite a pain. Sometimes things work just fine, sometimes everything seems out of control. Frustrating, right?

Intermittent starting issues highlights

• Level of urgency:Medium
• Can you drive?Yes
• DIY inspection:Impossible
• DIY repair:Impossible
• Price for repair:$300 - $600
• Common Reasons:Anykind ofstarting problem
• Ways to fix:Take it to professional mechanics and let them find the solution

What causes intermittent starting?

Intermittent starting can be caused by several factors, even though, at first, they might seem unrelated to the issue, since most people think that they have a faulty engine before they think of anything else. Here are some of the reasons the GMC Sierra might have intermittent starting:

• Bad positive/negative terminals

Even though you might have not messed with them in the past, with time and because of vibrations, they might have become loose, making contact with the contacts of the battery only from time to time.

• Faulty ground points

Ground points are one often overlooked cause not only of intermittent starting but also of many other electrical issues. After a certain period and usage, they might have become loose, or because of water ingress, they might be corroded, so they should be checked from time to time, regardless of the vehicle having an issue or not.

• Bad relays

Faulty relays will fail to activate the components they control and if they are on their last legs, they will almost certainly work only when they'll feel like it. It's better to check the relays before replacing the components they control since they are usually much cheaper and much easier to replace.

• Clogged fuel filter/fuel injectors

When was the last time you changed the fuel filter on your car? If the answer to this question is "I can't remember", then it's probably the right time to do so. This is usually a very cheap component to replace and most of the time it doesn't take a space engineer to do so. Also, bad fuel quality might have clogged the injectors, so they could also do with a cleanup.

• Dead battery

A battery that is no longer doing its job properly will become very temperamental. Sometimes, it won't prevent the engine from starting every single time you try to turn it over, but the issue can be intermittent.

• Bad starter

If the vehicle has been used mostly in towns with frequent on-and-off cycles, or if it's a bit older, or if you hear strange noises coming from the starter, then this might be your problem. Remember to check its ground point and its relay before deciding to replace it, since many times they are the actual culprits. Also, many times they can be refurbished by specialized shops, which should cost you less than buying a brand-new part.

• Faulty key fob

For the last few decades, cars have been equipped with clever key fobs and immobilizers, their role being to prevent starting the car without the use of an authorized key. If the key fob starts to fail because of age or because of physical damage, it might only work from time to time, thus making your engine start possible only from time to time as well.

• Bad ignition coils

Ignition coils provide the necessary electricity to the spark plugs for them to create the spark that causes the fuel to ignite. Since they are electrical and therefore can be quite temperamental, it would be a good idea to check them. Many times, they will also throw an error code. While in there, remember to check or even replace the spark plugs too.

• Bad ignition switch

A bad ignition switch could cause an intermittent starting problem, but it could also cause many other electrical components to behave in a very strange way. It might even stop the horn from working, or the buttons from the steering wheel, if it's the case.

• Faulty electric steering lock

Newer vehicles that don't have keys anymore and only have a button to start the engine are also fitted with electronic steering locks as opposed to the mechanical ones that were used before.

If they are on their last legs, they might fail to disengage from time to time, thus preventing the engine from starting. This is also a safety feature since you wouldn't want your steering wheel to suddenly lock up while driving, would you?

• Immobilizer issues

As mentioned above, in conjunction with a key fob, immobilizers are there to prevent unauthorized access to your vehicle. When they fail, they will almost certainly prevent the engine from starting, since the car's ECU won't be able to tell whether the actual key of the vehicle has been used or if someone simply decided to try with another one.

• Faulty fuel pump

Fuel pumps are one of those components that most of the time when they fail, they will simply do so without any prior warning. However, if you happen to hear strange noises coming from it, or if you encounter intermittent starting issues, it's a good idea to check it. As with the starter, always check the relay first.

• Bad crankshaft position sensor

The crankshaft position sensor is responsible for the actual running of the engine and if it were to fail, then the starting would become impossible since the ECU won't know the crankshaft's position and therefore it can't properly trigger the fuel injectors and the ignition coils at the right time.

There have been cases in which they failed due to long exposure to heat, usually giving signs such as intermittent starting before failing completely.

How to fix this problem?

Some of the possible causes can easily be investigated at home by any amateur mechanic, such as the ground points or the battery terminals. With the help of tools like a multimeter, the battery and the relays can also be checked quite easily.

However, when it comes to other components, you should be aware that there is no point in trying to guess which one of them is starting to fail since that would be a complete waste of time. The best thing to do, before anything else, would be to use a diagnostic tool. It will almost certainly tell you exactly what's wrong with the car, eliminating most of the other causes.

If you're not confident enough to attempt any of the mentioned operations at home, you don't have to worry, since pretty much any of your local shops will help you with this issue. Issues such as intermittent starting can be common in many vehicles, regarding their make and models, so this is not an issue specific to the GMC Sierra.

However, if you have the possibility, try to always go for a GMC specialist before going to any other shop, since such people have much more experience with these specific vehicles.

How to avoid this issue in the future?

Basically, avoiding this issue consists only of a couple of things, the first one is regular servicing of the vehicle, and the second one is regular checking of various components, such as the ground points that can become corroded or loose with time.

Other than that, most problems cannot be avoided simply by doing a certain operation and it would definitely be a waste of money to replace every single thing preventatively, especially when everything seems to work just fine. Also, you could end up buying a part that is of lower quality than what was originally fitted to your vehicle, thus increasing the chances of premature failure.

Is it safe to drive a car in this state?

This depends a lot on the actual cause of the intermittent starting. If the starter itself is faulty, while it can be annoying not being able to start the car as you normally could and having to push it, this wouldn't necessarily be one of the most dangerous things you could do (avoid, however pushing your car on busy roads!).

If we're talking about a faulty ignition lock, then we definitely recommend you have the vehicle towed to the nearest shop and avoid driving it. Even though it might have worked fine when you tried to start the engine, you might have a big surprise later if it decides to act up and suddenly engage while driving.

Final thoughts

Intermittent starting issues can be very frustrating, especially because, at first, it can be quite difficult to actually tell what exactly is wrong with the car. However, with a little bit of time and patience, most amateur mechanics out there should be able to find what the problem is. Local shops are also more than happy to help you in this regard.