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Discussion Starter · #1 ·
I have a 2002 Chevy trailblazer LS and it won't start. I've replace the alternator, starter, battery and starter relay and nothing. I really need help cause I been stuck in my car for four weeks. Any ideas?
 

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"Won't start" is far too vague.

You put the key in the ignition, turn the key, and ...? EXACTLY, what happens? Descriptions of sounds are helpful. Why did you replace all of that stuff? Just guessing? That gets expensive fast.

If you're looking at a key turn and it's just plain dead - like nothing at all happens, put in neutral and try again. See what happens.
 

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Does the engine turn over (referred to as cranking)?

Follow Joe_67's advice.
 

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Discussion Starter · #4 ·
When I try to start the car u only hear a click but very low click. Something is draining my battery. The reason I replace the alternator and starter is ok let me tell you what happen from start to end. I replaced my left front brake and about a few days later I felt I didn't put the brake on right so I went to fix it and when I was done I started my truck and had it in park and when I came back to my truck it turned off by itself and when I tried to start it nothing. But if my truck was parked for like overnight I would have to jump start my truck.. ok back to when truck stop working. So wouldn't start so changed the alternator first then the starter and it still won't start so went and got a new starter relay and nothing but the first thing i got was a new battery. Someone told me it the ECU. When I try starting the truck the lights that stay on are the air bag, abs, sit belt
 

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OK, thanks.

Now, please stop replacing parts and start diagnosing the problem. Could it be the ECU? Yes it could, but it could also be a lot of other things that are more likely to cause a no crank situation. Diagnosing the problem can actually save you a great deal of money in the long run.

In order to proceed, you will need a couple of specialized tools. One - an OBDII code reader/scanner, Two - a digital multimeter (DMM), and (this next one is nice to have on hand) an Automotive Logic Probe.

Here is a link to the Logic Probe:


It is just like a test light, but is computer safe and will let you know if power or ground is present rather than just power like with a test light.

So, do you have these tools?

Please respond so we can continue down the diagnostic tree.
 
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Discussion Starter · #8 ·
OK, thanks.

Now, please stop replacing parts and start diagnosing the problem. Could it be the ECU? Yes it could, but it could also be a lot of other things that are more likely to cause a no crank situation. Diagnosing the problem can actually save you a great deal of money in the long run.

In order to proceed, you will need a couple of specialized tools. One - an OBDII code reader/scanner, Two - a digital multimeter (DMM), and (this next one is nice to have on hand) an Automotive Logic Probe.

Here is a link to the Logic Probe:


It is just like a test light, but is computer safe and will let you know if power or ground is present rather than just power like with a test light.

So, do you have these tools?

Please respond so we can continue down the diagnostic tree.
Don't have Automotive logic probe
 

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OK. Sounds good! I purchased one a couple of years ago and it is very nice to have when checking for power or ground (especially ground).
 

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OK, now using your DMM, check and see what the battery voltage is when the engine is not running and the ignition key is in the OFF position. It should be at least 12.5 VDC. Now have a helper turn the ignition key to the start position and measure the battery voltage. What is it? If it is above 10.5 VDC the battery then the battery is likely good and is adequately charged.

Now, inspect both battery cables and make sure there is no green grunge disease at either end where the insulation meets the battery terminal or the connecting lug. You might want to see if you can lift the insulation slightly to see if you see any of the green grunge corrosion or if the wire is clean and shiny.

Now we get to see how well your battery cables are doing. With the negative lead of your DMM connected to ground, measure the voltage at each battery terminal using the DMM's positive lead. You should see battery voltage at the positive terminal that equals the battery voltage measured between the positive and negative terminals. You should see 0.00 VDC between vehicle ground and the negative battery terminal. If not, then inspect and clean the various connections going to the battery for both cables.

Now measure the voltage between vehicle ground and the positive cable at the junction box where you can connect a positive jumper cable should you need to jump start the vehicle. This voltage should match the battery voltage give or take a few tenths of a volt (say 12.5 VDC vs 12.45 VDC). Now move the positive meter lead to where the battery cable connects to the starter and measure the voltage. Again, this voltage should match the battery voltage give or take a few tenths of a volt.

OK, now take the meter's positive lead and measure the voltage at each end of the negative battery cable. You should see 0.00 VDC.

If any of the voltages are out of line, then the battery cable or cables are likely bad.

More steps coming. I just wanted to let you have something to begin with and let you know I am working the problem.

Good Luck & more soon.
 
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Attached are the starting and charging schematics for our vehicles. The systems are the same between 2003 and 2004.

I want you to have the schematics before I tell you what I would like you to check.

Circuit one, highlighted in yellow, is for the starter relay control circuit.

Circuit two, highlighted in sort of a purple color, is for the starter power circuit.
 

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Discussion Starter · #15 ·
OK, now using your DMM, check and see what the battery voltage is when the engine is not running and the ignition key is in the OFF position. It should be at least 12.5 VDC. Now have a helper turn the ignition key to the start position and measure the battery voltage. What is it? If it is above 10.5 VDC the battery then the battery is likely good and is adequately charged.

Now, inspect both battery cables and make sure there is no green grunge disease at either end where the insulation meets the battery terminal or the connecting lug. You might want to see if you can lift the insulation slightly to see if you see any of the green grunge corrosion or if the wire is clean and shiny.

Now we get to see how well your battery cables are doing. With the negative lead of your DMM connected to ground, measure the voltage at each battery terminal using the DMM's positive lead. You should see battery voltage at the positive terminal that equals the battery voltage measured between the positive and negative terminals. You should see 0.00 VDC between vehicle ground and the negative battery terminal. If not, then inspect and clean the various connections going to the battery for both cables.

Now measure the voltage between vehicle ground and the positive cable at the junction box where you can connect a positive jumper cable should you need to jump start the vehicle. This voltage should match the battery voltage give or take a few tenths of a volt (say 12.5 VDC vs 12.45 VDC). Now move the positive meter lead to where the battery cable connects to the starter and measure the voltage. Again, this voltage should match the battery voltage give or take a few tenths of a volt.

OK, now take the meter's positive lead and measure the voltage at each end of the negative battery cable. You should see 0.00 VDC.

If any of the voltages are out of line, then the battery cable or cables are likely bad.

More steps coming. I just wanted to let you have something to begin with and let you know I am working the problem.

Good Luck & more soon.
Something is draining my battery but the battery is new
 

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OK, now for the relay control circuit (highlighted in yellow). In order for the starter to crank when you turn the ignition key to the start position, a whole lot of engine systems parameters must be met and approved by the ECM. When everything is determined to be OK, the ECM commands the starter relay's control circuit to connect to ground in order to make the circuit complete.

Starting in the upper left hand corner of the schematic, you can follow the starter relay's control circuit. When the ignition key is turned to start, voltage is applied through Fuse 22, and current flows through the park-neutral switch and then to the starter relay control circuit. To make the circuit complete and allow current to flow, the ECM allows the ground side of the starter control relay control circuit to complete when that happens battery voltage is allowed to be applied to the stater solenoid's battery terminal (purple highlighted circuit).

Now starting at the lower right hand corner of the schematic, when the ECM sees that the cranking voltage circuit is complete, current flows from the ECM to Fuse 17 and then to the ignition switch. Current then comes out of the ignition switch and flows through the power side of the starter relay (relay 47) and then to the S terminal of the starter solenoid and this allows the starter solenoid to pull in the huge internal contact that is connected to the battery and then the engine cranks.

Following this, the engine should then start.

Now, if you have a no crank situation (which you do), you need to see if the ECM grounds Pin 48 in Connector C1 at the ECM connector. Using your DMM set to resistance, back probe ECM Connector C! Pin 48 and make sure it grounds when the ignition switch is turned to start. Next check to make sure that there is continuity between ECM Connector C1 Pin 48 and both sides of Fuse 22 in the underhood electrical center.

Now for the other side of the starter relay (the power circuit) begin by setting your DMM to resistance and back probe ECM Connector C1 PIn 31 with one test lead and then place the other test lead on the S Terminal on the starter solenoid (where the small gauge wire goes). You should not see continuity until your helper turns the ignition switch to start.

If you do not see continuity here when the ignition key goes to the start position, check and make sure that the ignition switch is not defective. You should see continuity between ECM Connector C1 PIn 31 and Pin D of the ignition switch connector at all times. When you turn the ignition switch to the run position, you should see continuity between ECM Connector C1 PIn 31 and Pin F of the ignition switch connector. If you do not, you have a defective ignition switch.

I'm also attaching diagrams for the above mentioned connectors.

Feel Free to ask any additional questions in case I've lost you.

Good Luck!
 

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OK, now on the subject of something that is draining your battery of power.

What really needs to be done is to use a DMM that will not turn itself off after 5 minutes of non-use, set up a parallel connection between the battery's battery post/terminal and the battery cable's terminal and then put the DMM in series with the battery and battery cable and then remove the parallel connection. This will serve to protect the HVAC actuators buried in the dash from being commanded to perform a calibration routine when power is restored and the internal nylon gears from breaking when the calibration procedure is commanded.

Now, after you have successfully set the DMM up as well as the parallel connection, disconnect the parallel connection and wait 30 minutes and then see what the current draw is from the battery and then start pulling fuses one by one to see which circuit is pulling the excess current.

OK, now for the battery warning and the rationale:

DO NOT DISCONNECT THE BATTERY - REMOVE THE APPROPRIATE FUSE(S). Why? Because when you reconnect the battery, the HVAC actuators inside of the dash are commanded to run a recalibration procedure which stresses the old brittle plastic gears inside the actuators and the brittle plastic gears break and leaves you unable to control where the air comes out, or control the temperature of the air, etc. Replacing at least one of them literally requires the removal of the entire dash! So, if you ever need to actually disconnect the battery, such as in the case of needing to install a new battery, be sure and use some kind of Keep Memory Alive device to avoid the HVAC actuator recalibration routine.
 

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Discussion Starter · #19 ·
OK, now on the subject of something that is draining your battery of power.

What really needs to be done is to use a DMM that will not turn itself off after 5 minutes of non-use, set up a parallel connection between the battery's battery post/terminal and the battery cable's terminal and then put the DMM in series with the battery and battery cable and then remove the parallel connection. This will serve to protect the HVAC actuators buried in the dash from being commanded to perform a calibration routine when power is restored and the internal nylon gears from breaking when the calibration procedure is commanded.

Now, after you have successfully set the DMM up as well as the parallel connection, disconnect the parallel connection and wait 30 minutes and then see what the current draw is from the battery and then start pulling fuses one by one to see which circuit is pulling the excess current.

OK, now for the battery warning and the rationale:

DO NOT DISCONNECT THE BATTERY - REMOVE THE APPROPRIATE FUSE(S). Why? Because when you reconnect the battery, the HVAC actuators inside of the dash are commanded to run a recalibration procedure which stresses the old brittle plastic gears inside the actuators and the brittle plastic gears break and leaves you unable to control where the air comes out, or control the temperature of the air, etc. Replacing at least one of them literally requires the removal of the entire dash! So, if you ever need to actually disconnect the battery, such as in the case of needing to install a new battery, be sure and use some kind of Keep Memory Alive device to avoid the HVAC actuator recalibration routine.
How do I check to see if the starter is good cause I got it from pick n pull?
 

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Is the starter on or off the vehicle?
 
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