Aura won't crank

[imaddicted2u]

The radio on your car is turned on/off by the BCM.

U0100 could have been caused by the low battery voltage while cranking.

[rochvids]

Originally Posted by imaddicted2u

The radio on your car is turned on/off by the BCM.

U0100 could have been caused by the low battery voltage while cranking.

Update: Engine is not seized.

The reason I think I should focus on the BCM is because the starter solenoid gets power when hooked directly from the battery or jump started from the relay. When I turn the ignition to start, power should be sent through the purple wire, which I believe is coming from the ignition. Let's assume that the starter is bad, when I turn the key, why no power is sent through the ignition wire? I did 2 tests to confirm this:

1. I unplugged the wire from the starter, hooked a multimeter to it, then tried to start the car, no power.

2. I connected a wire directly from the battery to where I unplugged the purple wire, and the starter was trying to crank the engine.


Would you happen to have a wiring diagram of the ignition system? I'm just trying to figure out how the BCM is wired and if it can interfere with the ignition system.

[fdryer]

This may help; http://www.saturnfans.com/forums/sho...d.php?t=234451. Severely corroded ground lug with wires disintegrating, electronic starting circuit controlled by the ecm. PNP is the park neutral switch. I'm presuming Aura starting circuits are the same for the model years.

[imaddicted2u]

Good it's not seized. You may well have a BCM problem too but step one is still to get the starter working right otherwise you'll never know when you are making headway with starting with the key.
The starter should spin the engine when jumped at the relay, irregardless of the BCM. It's connected directly from the battery to the solenoid. This has the all the symptoms of a bad contact inside the solenoid.
Jump across the two large studs on the starter, if it turns the engine now, it's a bad solenoid.
Pull the starter off the engine, hook it up with booster cables and see if it turns.
The red line in the pic is the path the jumper takes, bypassing the start relay.
The green line in the pic is the path when touching the two studs on the starter together, bypasses the solenoid contact.
Of course this all assumes the basics, that the ground connection from the battery to the engine block and that the positive connection from the battery to the starter are in good shape.

[imaddicted2u]

Originally Posted by rochvids

Update: Engine is not seized.

The reason I think I should focus on the BCM is because the starter solenoid gets power when hooked directly from the battery or jump started from the relay. When I turn the ignition to start, power should be sent through the purple wire, which I believe is coming from the ignition. Let's assume that the starter is bad, when I turn the key, why no power is sent through the ignition wire? I did 2 tests to confirm this:

1. I unplugged the wire from the starter, hooked a multimeter to it, then tried to start the car, no power.

2. I connected a wire directly from the battery to where I unplugged the purple wire, and the starter was trying to crank the engine.


Would you happen to have a wiring diagram of the ignition system? I'm just trying to figure out how the BCM is wired and if it can interfere with the ignition system.

Your test 2 is the same as hooking the jumper at the relay...the engine should have spun like crazy, not just tried to crank the engine, did it still sound like the audio clip you posted earlier?

[rochvids]

Originally Posted by fdryer

This may help; http://www.saturnfans.com/forums/sho...d.php?t=234451. Severely corroded ground lug with wires disintegrating, electronic starting circuit controlled by the ecm. PNP is the park neutral switch. I'm presuming Aura starting circuits are the same for the model years.

I looked into the parking neutral switch, no issues there. Same symptoms even when I put it in neutral.

I also replaced all ground wires and made sure everything is making good contact. I left nothing unchecked, voltage and resistance wise. The only wire that's not receiving power is the ignition/signal purple wire that's going to the starter.

[rochvids]

Originally Posted by imaddicted2u

Good it's not seized. You may well have a BCM problem too but step one is still to get the starter working right otherwise you'll never know when you are making headway with starting with the key.
The starter should spin the engine when jumped at the relay, irregardless of the BCM. It's connected directly from the battery to the solenoid. This has the all the symptoms of a bad contact inside the solenoid.
Jump across the two large studs on the starter, if it turns the engine now, it's a bad solenoid.
Pull the starter off the engine, hook it up with booster cables and see if it turns.
The red line in the pic is the path the jumper takes, bypassing the start relay.
The green line in the pic is the path when touching the two studs on the starter together, bypasses the solenoid contact.
Of course this all assumes the basics, that the ground connection from the battery to the engine block and that the positive connection from the battery to the starter are in good shape.

Thank you for the diagram and info!

Back to the voltage drop, it was trying too hard because both the alternator and the A/C pulleys are frozen! It's been sitting for months and through the freezing winter, that's probably why. I removed the serpentine and I turned the engine by hand easily, and I didn't even have to remove the spark plugs.

It cranks just like yours, but there is one issue. It does so with or without the key. I'm going to get gas because judging by the needle and the low fuel light, the tank is probably empty. I will post back after I put gas in and try to start it.

[rochvids]

Originally Posted by imaddicted2u

Your test 2 is the same as hooking the jumper at the relay...the engine should have spun like crazy, not just tried to crank the engine, did it still sound like the audio clip you posted earlier?

That makes sense.

It's doing exactly as you mentioned. Take a listen: https://sndup.net/3n24

[imaddicted2u]

Originally Posted by rochvids

Thank you for the diagram and info!

Back to the voltage drop, it was trying too hard because both the alternator and the A/C pulleys are frozen! It's been sitting for months and through the freezing winter, that's probably why. I removed the serpentine and I turned the engine by hand easily, and I didn't even have to remove the spark plugs.

It cranks just like yours, but there is one issue. It does so with or without the key. I'm going to get gas because judging by the needle and the low fuel light, the tank is probably empty. I will post back after I put gas in and try to start it.

When you jumper it to start it will turn with or without the key. If the engine and electronics are capable(and it has gas) it will start when jumpered with the key on. This method bypasses the neutral switch insdide the park neutral switch.
Does it crank when you turn the key now or no? Hard to keep track
Good you got it cranking. Now you can do some proper troubleshooting. One step at a time.

[imaddicted2u]

Originally Posted by rochvids

I looked into the parking neutral switch, no issues there. Same symptoms even when I put it in neutral.

I also replaced all ground wires and made sure everything is making good contact. I left nothing unchecked, voltage and resistance wise. The only wire that's not receiving power is the ignition/signal purple wire that's going to the starter.

The side of the PNP switch in the circle is used by the ECM to determine is the transmission is in park or neutral. The other side is used by the TCM to determine what gear is selected.
Two ways to test it:
1. With an ohmmeter and the connector still plugged in...measure from pin 1 (black/white wire) to the engine block. You should have 0 or near 0 ohms. Next measure from pin 12 (orange/black wire). With the car in park measure You should have 0 or near 0 ohms. Perform the same check with the car in gear and you should have infinite/open resistance.
or
2. With the meter on volts...test from pin 12 (orange/black wire) to the engine block. You should have 5 or 12 volts, can't remember which, when in gear and 0 volts when in park or neutral.

Any faults with this switch or wiring will prevent the starter relay in the fuse box from engaging when you put the key to start, so no power goes to the purple wire on the starter.

[rochvids]

Originally Posted by imaddicted2u

When you jumper it to start it will turn with or without the key. If the engine and electronics are capable(and it has gas) it will start when jumpered with the key on. This method bypasses the neutral switch insdide the park neutral switch.
Does it crank when you turn the key now or no? Hard to keep track
Good you got it cranking. Now you can do some proper troubleshooting. One step at a time.

Yes, it cranks just like yours. See Post #68 for the audio. And yes, it cranks with the key on, it won't start though.

[rochvids]

I put gas in it, tried to start it, nothing. It still cranks.

I checked the fuse in the trunk, it's good and the fuel pump relay clicks when I turn the key on. I also checked schrader valve in the fuel rail, and it had only a couple of drops of gas, which I believe were left from last time it died. I sprayed some starting fluid and it started for like a second.

Can you hear the fuel pump humming when you turn the key on? I never paid attention on this car, I know some are very quiet.

[imaddicted2u]

Making good headway.
I just went and cycled the key on and off. All I hear is a little tick sound, no hum or anything.
Try this. Pull the fuel pump relay. Determine which are the two switched contacts. Set up your multimeter to measure amps. Insert your probes in the fuse box where the switched contacts on the relay would go. The pump should run and you should be reading the current draw of the pump through the meter. You may need the key on and it's important to only put the meter across the switched contacts.

[rochvids]

Originally Posted by imaddicted2u

Making good headway.
I just went and cycled the key on and off. All I hear is a little tick sound, no hum or anything.
Try this. Pull the fuel pump relay. Determine which are the two switched contacts. Set up your multimeter to measure amps. Insert your probes in the fuse box where the switched contacts on the relay would go. The pump should run and you should be reading the current draw of the pump through the meter. You may need the key on and it's important to only put the meter across the switched contacts.

Thank you, we're getting there.

I bridged the relay diagonally to give power to the fuel pump, and because I was in the trunk, I could hear it humming. I went beck under the hood and checked the fuel rail, it had plenty of gas. I tried to start it, still just cranking. At this point I am thinking either the fuel injectors are turned off or there is no spark. I am going to check for spark today and make sure the spark plugs are firing. What's interesting is that when I sprayed the starting fluid initially, it started for a second, now it wouldn't, maybe the fuse for the coil packs is now blown? I will go back to testing the reply as you described, I just want to make sure the ignition system is working as it should so I can focus on fuel.

[imaddicted2u]

Now that you are at this stage...is the check engine light on? Are there any codes?
This link should match your fuel injector circuit and has some other handy injector testing info.
https://easyautodiagnostics.com/gm/2...cuit-diagram-1
This link is on coil testing.
https://easyautodiagnostics.com/gm/2...n-coil-tests-1

[rochvids]

Still working in it... I will post results tomorrow.

[rochvids]

Originally Posted by imaddicted2u

Now that you are at this stage...is the check engine light on? Are there any codes?
This link should match your fuel injector circuit and has some other handy injector testing info.
https://easyautodiagnostics.com/gm/2...cuit-diagram-1
This link is on coil testing.
https://easyautodiagnostics.com/gm/2...n-coil-tests-1

I tested all coils, there is no spark. I applied power to the trigger wire on one of the coils, but it did not produce any spark. I have not tested the fuel injectors yet as I wanted to focus on getting the spark plugs to fire up first.

I used a test light to make sure all ground wires are making good contact, including the engine block, no issues there. The battery is at 12.6, and as you heard it, it cranks and there is no shortage of power.


While I was testing the ignition the coils, I noticed the check engine light does not light up when I turn the key on. When I plugged in the scanner, the code of lost communication (U0100 Lost Communication With ECM/PCM A) was thrown again. Now I am thinking it's the ECU.

I did some further testing with ECU as shown in this video: https://www.youtube.com/watch?v=mYBzj086Ips. I don't have the tool that he has but if you skip over to 7:30, the testing he does on the wires reflects mine exactly. I have good connection to the connector, there are no bent pins, there is no corrosion, everything looks clean.

[imaddicted2u]

If the engine cranks but doesn't start with the key. The ECM must not be completely dead.
If the engine cranks but doesn't start with the key. There must be some communication, at least between the ECM amd BCM, since the ignition switch is wired to the BCM and start circuit is wired to the ECM.
Since it tried to fire before with starting fluid, Try disconnecting the battery cables and hold the + and - together for a few minutes to ensure all circuits are depleted. Then reinstall the + then the - on the battery. Read the codes to see if U0101 has reappeared. Try to start is, cross your fingers, see what happens.
I've read some things about the GMLAN network being impacted by the reference voltage being pulled down by faulty sensors, bad communication grounds, bad B+ to modules, shorted network connections and often a failed ECM as in this Malibu video.
https://www.youtube.com/watch?v=5--r_W0w9mE

[rochvids]

Originally Posted by imaddicted2u

If the engine cranks but doesn't start with the key. The ECM must not be completely dead.
If the engine cranks but doesn't start with the key. There must be some communication, at least between the ECM amd BCM, since the ignition switch is wired to the BCM and start circuit is wired to the ECM.
Since it tried to fire before with starting fluid, Try disconnecting the battery cables and hold the + and - together for a few minutes to ensure all circuits are depleted. Then reinstall the + then the - on the battery. Read the codes to see if U0101 has reappeared. Try to start is, cross your fingers, see what happens.
I've read some things about the GMLAN network being impacted by the reference voltage being pulled down by faulty sensors, bad communication grounds, bad B+ to modules, shorted network connections and often a failed ECM as in this Malibu video.
https://www.youtube.com/watch?v=5--r_W0w9mE

It cranks but only if I jump the starter relay. With the key on, it cranks but does not start. If trying to start it with they key on, it does not do anything.
I disconnected the cables and held them as you mentioned, U0101 reappeared. I will check out the video, thank you.

Question, if it is the ECU, does it need to be reprogrammed if I pull one from the salvage yard?

[imaddicted2u]

ECU must be programmed to the vehicle. Some ebay and Amazon sellers ship ECMs programmed, you provide the VIN of the car to them.