A little help with my son’s 2003 Tahoe

[Ash4l]

Hello, my son is having a little trouble out of his 2003 Tahoe. It died on him the other day and we suspected fuel pump because we didn’t hear the pump coming on. We replaced the pump but still no power to pump. Today we hot wired the pump to get it to run but it would still not crank. All fuses and relays seem to be fine. It will try to crank once then when you shut it off again and turn the switch there’s nothing. Any help would be appreciated.

 

[Fless]

Welcome to the forum from Colorado!

Verify that the battery is fully charged and has cranking capacity. How old is it, and has it been tested lately?

Did the pump run when you hot wired it? Use a fuel pressure gauge while you hot wire the pump to see if it runs and brings the pressure up.

I suggest bypassing the starter relay to see if the main cables are intact and can handle the current. This thread shows how to do that, but there will be several YouTube videos, so do some searching if you'd rather:

no crank no start intermittent problem

Sorry to bring this thread back from the dead. My truck does the same thing but it will start with my remote start with no problems. I replace the starter last winter. Should I be looking at the ignition switch? Thanks That would be a good place to look. I don't know what year make/model your...

www.tahoeyukonforum.com

I'd also suggest doing a voltage drop test:

 

[Ash4l]

Thanks for the reply! Yes. The battery is good. It is only about 2 months old. The pump ran when it was hot wired. I’ll look over the video and try that when we get back to it.

 

[rockola1971]

After checking Ign A and Crank Fuse and both negative and positive cable battery connections at the battery, starter and engine block ground(corrosion is usually the culprit here), I would suspect the ignition switch. If you are familar with how to use a voltmeter I can tell you where to check using the following schematics. I own (2) 2003 Tahoe LT's.

 

[Ash4l]

we changed the ignition switch about a year ago. I guess it could have gone bad in that time. We’ll check everything you suggested and maybe replace the switch again.

 

[Fless]

we changed the ignition switch about a year ago. I guess it could have gone bad in that time. We’ll check everything you suggested and maybe replace the switch again.

Have @rockola1971 get you some test info before condemning the switch. In my experience there's nothing worse than introducing new parts as variables.

 

[Ash4l]

Yeah. I would take all the info I can on what to check with a meter.

 

[rockola1971]

Ckeck for 12v at dark green/white wire terminal of fuel pump relay socket. This will be the coil terminals of the relay. One will be ground and the other 12v when ignition is turned to crank. You will have to check this with relay pulled out. Other 2 terminals will be 12v hot at all times and the other is the feed for 12v to your fuel pump. While you have fuel pump relay pulled measure resistance of coil of relay. Diagram on side of relay will tell which 2 terminals lead to the coil.

 

[Ash4l]

I don’t think it’s the wiring of the fuel pump that’s bad. We changed out the ignition switch thinking it may be it. I was wrong about changing it earlier. It was the ignition lock. I couldn’t remember, anyways that wasn’t the cause. We bypassed the relay and and had full voltage on the lines. Something somewhere is causing it not to get the power all the way around to run. It’s very strange. Never had anything like this before.

 

[rockola1971]

I don’t think it’s the wiring of the fuel pump that’s bad. We changed out the ignition switch thinking it may be it. I was wrong about changing it earlier. It was the ignition lock. I couldn’t remember, anyways that wasn’t the cause. We bypassed the relay and and had full voltage on the lines. Something somewhere is causing it not to get the power all the way around to run. It’s very strange. Never had anything like this before.

I went back through your post and it appears you have no crank or intermittent cranking issue. When it comes to relays there are actually 2 circuit going to a relay. Usually a high amp circuit for feeding power to (in this case) a fuel pump and then a low amp (control circuit) to the coil. They are separate from each other. The fuel pump is fed directly from its own fuse. The coil to the Fuel Pump Relay is fed from the PCM after certain conditions are met. The PASSLOCK security system does NOT disable engine crank like most aftermarket alarm systems operate. It strictly disables the fuel pump after 5-10 seconds if the PASSLOCK is not happy or defective.

Quick and dirty check here is check for 12v on small wire (S terminal) of starter solenoid while someone is trying to crank engine. This will tell us whether we have a starter issue or a control issue. Do this check with a fullly charged battery.

 

[Fless]

I may have missed it or simply don't understand.

Is this a "fuel pump doesn't run" or fuel pump runs but "no crank?" Or "fuel pump doesn't run" AND the engine won't crank over?

 

[Ash4l]

Ok thanks! We probably won’t tinker with it until next weekend because it’s at my fathers house and with my work hours I won’t have time til then.

 

[Ash4l]

It’s more of I don’t know what’s causing the issue. Lol

First we thought fuel pump. No power to the pump. Changed pump and still doing it.

So we straight wired the new pump and worked great but won’t start up. It will try turning over sometimes and sometimes it won’t.

Grabbed another ecm from junk yard and tried that as well and also tried changing the ignition switch.

I feel it’s an electrical or grounding issue but I have no idea where to look.

 

[Fless]

If you bypass the starter relay, will it crank over solidly?

Have you tried the voltage drop test that I posted in an earlier post?

"Plan the work, and work the plan." -- Eric O. SMA

 

[houstontaylor]

On my 2003 Tahoe I have had fuses that did not work due to oxidation of the aluminum prongs on them. It's cheap enough to replace the fuses in the affected circuit as a precaution. Aluminum oxide is non conductive.

 

[Jeff O]

I believe the fuel pump initially charges pressure as soon as the key is inserted, the idea is that this means start is coming next. It seems the troubleshooting has already eliminated that function. I would check the main computer connectors for corrosion, especially on the lowest terminals. This fixed my problem of lack of pressure and shutdowns with no start cranking afterward.. You will note the poor placement of the main computer and its relative lack of total protection mounted on the left frame next to engine.

 

[Ash4l]

I picked my son up after work today since I had some day light left. Tried cleaning the connectors to the computer. Didn’t work.

I started jiggling some of the wires around to see if I could find a short and get the power back to the fuel pump and now it just clicks when you try to turn it over. I’m almost positive it’s coming from that wiring harness from the back all the way to the fuse box.

My son told me my volt meter was in his vehicle and now he can’t find it. So I wasn’t able to check anything today

 

[rockola1971]

If the "clicking" is coming from the starter then you have a low battery, dirty/loose connection at one of the battery cables (either end) or a Bad starter. *READ WARNING BELOW* You can take a wrench and lay it across both large terminals of the starter and it should crank the engine (wont start though). During this test nobody is needed to do anything with the key. A good starter, battery and cable connections will cause the starter to immediately spin engine over when you touch both large terminals with the wrench.

*WARNING* The 2 large terminals on the starter consist of one that is directly connected to the positive of your battery (NO SWITCH AT ALL BETWEEN THEM) and the other large terminal is connected internally to your starter motor winding. DO NOT LET THE WRENCH TOUCH ANYTHING BUT THOSE 2 LARGE TERMINALS. BEWARE OF TOUCH THE ENGINE BLOCK OR ANY OTHER METAL NEAR THE AREA! If you do, you will find out the hard way what happens when you essentially lay a wrench across the battery terminals. SPARKS EVERYWHERE AND THINGS GLOW CHERRY RED.

 

[rockola1971]

I picked my son up after work today since I had some day light left. Tried cleaning the connectors to the computer. Didn’t work.

I started jiggling some of the wires around to see if I could find a short and get the power back to the fuel pump and now it just clicks when you try to turn it over. I’m almost positive it’s coming from that wiring harness from the back all the way to the fuse box.

My son told me my volt meter was in his vehicle and now he can’t find it. So I wasn’t able to check anything today

The fuel pump should kick on for 3-5 seconds when ignition is switched to run.(Prime) During crank position the fuel pump is on full time. Listen for the fuel pump to turn on when someone switches the ignition to run for you. You can pull the gas cap and hear it really good that way, while NOT smoking.

 

[NardDog]

Hello, my son is having a little trouble out of his 2003 Tahoe. It died on him the other day and we suspected fuel pump because we didn’t hear the pump coming on. We replaced the pump but still no power to pump. Today we hot wired the pump to get it to run but it would still not crank. All fuses and relays seem to be fine. It will try to crank once then when you shut it off again and turn the switch there’s nothing. Any help would be appreciated.

So when the pump is “hotwired” HOW were you able to confirm that was OR wasn’t fuel getting to the top of the engine into the rails? With that in mind consider the checking fuel regulator on the fuel rail atop the engine. Could have failed shut.