Will not start when hot?

MARIA9116

MEMBER
2009 PONTIAC G6
3.5L
6 CYL
2WD
AUTOMATIC
150,000 MILES

A few weeks ago, my car wouldn’t start, we got the starter tested it tested bad, so we installed a new one.
Ever since installing the new starter, the car will not start when it is hot. It will cold start every time and after driving short distances. If the car has been on for a while and I shut it off to pump gas or run into the grocery store it will not start until it cools off down. The car is not overheating, the battery, alternator and starter are all fairly new. The check engine light is not on, and the car throws no codes at all.
I suspect Vapor lock but don’t think that’s a thing with fuel injected vehicles.

3 Replies

JACOBANDNICKOLAS

MECHANIC
108,217 POSTS

Hi,

When you say it won't start when at operating temperature, do you mean the starter won't engage or does it engage but the engine fails to run?

If it fails to run, my first suspect is a faulty crankshaft position sensor. When they begin to fail, heat adversely affects them. As a result, the ignition spark is lost, and you need to wait until it cools off for it to run again.

Do me a favor. Take a look through this link and let me know if it seems to mirror what you experience:

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

If it does seem to mirror what you experience, I attached the directions below specific to this vehicle for the replacement of the sensor.

On the other hand, if it is the starter motor that won't work, let me know that as well.

Take care,

Joe

See pics below.

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Tuesday, August 8th, 2023 AT 10:08 PM

MARIA9116

MEMBER
2 POSTS

When I say it won’t start, I mean no crank at all. It most happens in the afternoon when the sun is hottest. Yesterday I drove it to a few places in the morning and it started with no problems. When I got home around 1:00pm I shut the car off and tried restarting it just to check and it wouldn’t turn on until about 5:00pm when the sun was starting to go down.

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Wednesday, August 9th, 2023 AT 5:39 AM

JACOBANDNICKOLAS

MECHANIC
108,217 POSTS

Hi,

Okay, so the starter doesn't engage. First, take a look at link 1. It covers different possibilities that can cause the starter to fail when hot. Also, link two explains what and how to check the starter motor:

https://www.2carpros.com/articles/comprehensive-guide-why-doesnt-your-car-engine-crank-when-hot-and-how

https://www.2carpros.com/articles/starter-not-working-repair

The issue could be the result of a faulty starter relay. This is an easy thing to check but should be done when the starter won't engage.

I attached a pic below of the fuse box under the hood. I highlighted the starter relay. Switch it with a different relay having the same part number and see if the starter then engages. If there isn't a relay with the same part number, here is a link that explains how to test one:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know what you find.

Take care,

Joe

See pic below.

Image (Click to make bigger)