Engine won't crank over

It sounds like there may be an issue with the ignition system on your 2005 Pontiac Sunfire. Here are a few potential causes for the problem you're experiencing:

1. Faulty ignition switch: The ignition switch is responsible for sending power to the starter, so if it's not working properly, the engine may not crank.
2. Bad starter solenoid: The starter solenoid is responsible for engaging the starter when you turn the key, if it is not functioning properly, the engine will not crank.
3. Wiring problem: If there is a problem with the wiring leading to the starter or ignition switch, it can prevent the engine from cranking.
4. Failed crankshaft position sensor: This sensor is responsible for relaying the engine's position to the car's computer. A bad sensor can cause a no-start condition.
5. Failed PCM (Powertrain Control Module) that can prevent the engine from starting.

It's likely that one of these issues is causing the problem you're experiencing, but it can be difficult to diagnose without proper testing. It would be best to take it to a professional mechanic for proper diagnosis and repair.

When you turn the key to the start position what's happens ? Nothing , do the lights dim ,dome light ? The starter doesn't engage an spin the engine ? Is the security light lit on the instrument cluster ? Anti-theft system problem may disable starter engagement . You say battery is good ? How do you know ? Headlamps shine bright ? Do you know how the starter circuit works ? Does it use a key start ?
Circuit Description (Key Start)
When the ignition switch is placed in the Start position, a discrete signal is supplied to the body control module (BCM) notifying it that the ignition is in the Start position. The BCM then sends a message to the engine control module (ECM) notifying it that CRANK has been requested. The ECM verifies that the transmission is in Park or Neutral. If it is, the ECM then supplies 12 volts to the control circuit of the crank relay. When this occurs, battery positive voltage is supplied through the switch side of the crank relay to the S terminal of the starter solenoid.

https://www.youtube.com/watch?v=SNLcW7FhQFw&t=17s

The starter won't crank. If nothing happens when you turn the ignition key to the "Start" position, it means that the starter motor doesn't turn over the engine. Most commonly this could be caused by a dead battery; here is How to check the battery. ... The starter solenoid control wire could have a bad connection. Why car won start troubleshooting tips

hi Roy.
The starter won't crank. If nothing happens when you turn the ignition key to the "Start" position, it means that the starter motor doesn't turn over the engine. Most commonly this could be caused by a dead battery; here is How to check the battery. ... The ignition switch could be bad - it's a common problem.13 Aug 2013

Why a car won't start - troubleshooting tips - Samarins.com

How do you fix a car that won t start?
When your car responds with silence or clicking:

1. Turn on the car lights. ...
2. Tighten and clean the battery connections and try again. ...
3. Jump start the car.
4. If this works, immediately have the battery tested, especially if it's old. ...
5. Things could still be worse - such as a bad starter or alternator.

Car Won't Start? Here's What You Should Do ' GEICO

https://www.geico.com/more/driving/auto/auto-care/what-to-do-if-your-car-wont-start/ Search for: How do you fix a car that won t start?

Turning ignition switch to start position ! Nothing happens , no click , nothing ?
Circuit Description
Moving the ignition switch to the CRANK position sends a 12 V signal to the PCM Ignition Crank Sense. The PCM verifies that the transmission is in the PARK or NEUTRAL position. The PCM then grounds the control circuit of the START relay. When the START relay is energized it allows voltage to the starter solenoid S terminal.

Starter Solenoid Does Not Click

2
Turn the ignition to the START position.
Does the engine crank?
YES - Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
NO - Go to Step 3
3
Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the Crank Request Signal parameter in the PCM data list.
Turn the ignition to the START position.
Does the scan tool display Yes?
YES - Go to Step 5
NO - Go to Step 4
4
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the Crank Request Signal parameter in the PCM data list.
Turn the ignition to the START position.
Does the scan tool display Yes?
YES - Go to Step 11
NO - Go to Range Selector Displays Incorrect Range in Automatic Transaxle - 4T80- E
5
Turn OFF the ignition.
Disconnect the Starter relay.
Turn ON the ignition, with the engine OFF.
Connect a test lamp between the battery positive voltage of the Starter relay coil circuit and a good ground.
Does the test lamp illuminate?
YES - Go to Step 6
NO - Go to Step 19

This is troubleshooting info from GM factory service testing and repair manual .A scan tool isn't necessary , you could use a test light if you knew which pins at the PCM . For example , testing Crank Request Signal parameter in the PCM data list. Find this wire circuit at the PCM , with a test light .When turning the key to start position ,does the test light light ? A factory scan tool just cuts down the time of diagnoses . A wiring diagram is a must for diagnosing this . Free wiring diagrams can be found at
http://www.bbbind.com/free_tsb.html There are videos on youtube on basic automotive electrical trouble shooting , Control module diagnostics . That is if you don't know how to already .

Ignition switch....the electrical ignition switch. To verify, find the thick white wire in the harness coming from the switch and do two things; first, check for power at this wire, when you switch the key position to start. If nothing, power the wire momentarily with the key in the run position, and your car should start.

What you are saying is the key switch is worn out, and there is a separate problem with the engine performance.
Either an import shop or the dealer are your options here.

not sure if any off this will help you o The starter won't crank. If nothing happens when you turn the ignition key to the "Start" position, it means that the starter motor doesn't turn over the engine. Most commonly this could be caused by a dead battery; here is How to check the battery. ... The ignition switch could be bad - it's a common problem.13 Aug 2013

Why a car won't start - troubleshooting tips - Samarins.com

www.samarins.com/diagnose/ut...or try this link. Car wont start Google Search

You mean that the starter is turning (cranks) the engine but the engine won't start? Be sure it is getting fuel. Turn the key to the on position and you should hear the fuel pump in the fuel tank run for a few seconds. If so that is good. If the fuel is being delivered then possibly you have no spark which usually is the electronic ignition module. The only way to test it is to replace it. Your timing chain or belt could be broken or "jumped" as the third possibility. I am leaning toward ignition module being bad as they just die without warning and nothing can revive them.

Ignition switch maybe ? Do you know how to do automotive electrical testing with a volt meter ? Pull the covers off the steering column to get at ignition switch electrical connector , then look at a wiring diagram to see which wires should have B+ voltage in the on - run position ! See if the B+ voltage drops out or just isn't there . You can find free wiring diagrams here
http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model and engine . Under system click electrical distribution ,then under subsystem click on power distribution .Click the search button then the blue link . scroll down the diagrams till you see any that show the ignition switch . Check all the wires that should have B+ power in the run position . I know GM has had ignition switch issues .
The starting of the vehicle is computer controlled ,when you turn the key to start ,this sends B+ voltage to the PCM - engine computer which will then energize the starter relay ,thier by cranking the engine .