99 Chevy S10 Relay Diagram
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Discussion Starter · #1 ·
Ok the backstory. I have a 2000 S10 xtreme and last week while driving down the road it just died on me out of nowhere. Got it to a parking lot and cycled the key and don't hear the usual fuel pump prime signal.
Been there done that, I'm thinking it's the ECM B Fuse, Fuel Pump Relay or Fuel Pump. Got the truck home after checking the fuse and swapping relay with a new one, then moved on to swap out the fuel pump. After finishing all that, still no fuel pump prime noise sent to fuel pump.
Back at the fuse panel, double checking that I have constant to the ECM B fuse (Good). Checked for the constant on signal at relay pin (Good). Made a Jumper wire from the constant on relay to the Fuel Pump Prime pin and Fuel Pump runs fine (Great). So this tells me that the wiring and circuit is good from the relay to the fuel pump so now I'm looking at the ECM side of the relay wiring.
Now I check the Ground side pin for the fuel pump relay and that seems fine. I also checked the ground wire off the MAF sensor as it uses the same ground and while there I get a 5V reference signal from the yellow MAF sensor wire to the ECM.
So here's the part I'm thinking is very strange. I have my test light hooked up to the input pin of the fuel pump relay and cycle the key to see the 2 second prime signal. What I'm getting is a split second pulse of a signal being sent to the fuel pump relay. I'm guessing this is not normal and I should see a full 2-3 second prime signal right?
So from there I do more testing at the wiring harness at the ECM. I'm getting ground, I'm getting an always on from the orange wire, I'm getting Key On signal to the Dark Green/White wire.
I'm running out of ideas of what and where to check for problems. Please let me know of any other ideas. I feel like if I can get the fuel pump prime signal worked out, then everything else will fall in place.
Thanks!
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You may be needing a new ignition switch. The contacts inside build resistance over time due to carbon build up from arcing and can cause the issue you are having.
When the contacts go bad
For the 98+ trucks, the most common issue is the "security" light on the dash illuminating. But the problem can also manifest itself as an inoperative fuel pump, unresponsive cluster, ABS and/or SIR lights being illuminated on the cluster, as well as a no start condition (either related to the inoperative fuel pump or a failure of the starter to turn over). The ignition switch can also cause PASSLOCK issues.
Looks like this:
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Discussion Starter · #3 ·
You may be needing a new ignition switch. The contacts inside build resistance over time due to carbon build up from arcing and can cause the issue you are having.
When the contacts go badFor the 98+ trucks, the most common issue is the "security" light on the dash illuminating. But the problem can also manifest itself as an inoperative fuel pump, unresponsive cluster, ABS and/or SIR lights being illuminated on the cluster, as well as a no start condition (either related to the inoperative fuel pump or a failure of the starter to turn over). The ignition switch can also cause PASSLOCK issues.
Looks like this:
Thanks for the response. I forgot to mention in the original post that the engine is cranking over so I didn't think it could be that harness but I'll start probing wires with a multimeter and see if anything unexpected shows up from there.
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The MAF shares ground with A/C. Fuel pump grounds at the back on the frame rail drivers side.
When the ignition is initially turned to the RUN position, the PCM activates the fuel pump relay by applying battery voltage through the dark green/white stripe wire for 2 to 3 seconds. If the PCM does not receive data from the crankshaft position sensor during this time, it will deactivate the fuel pump relay. While the relay is activated, battery voltage from ECM B 20 amp fuse is applied to the grey wire that runs directly to the fuel pump.
The fuel pump relay should be activated continuously when the ignition is in the START position.
My truck would crank over fine and run. It would shut off briefly as I was driving. Very scary. There are 4 contacts inside that power different circuits.
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Discussion Starter · #5 ·
I was referring to the ground off the control side of the fuel pump relay.
So if the crankshaft position sensor is bad, that could likely be the cause of my problems then?
ECM tries to send prime signal to the fuel pump relay but crankshaft position sensor interrupts it immediately?
I'll check that sensor first thing in the morning.
Thanks a ton!
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Discussion Starter · #7 ·
I noticed some frayed wiring at the connector for the crank sensor, so that's getting replaced anyways when the part shows up today.
So a bad ignition switch can result in no fuel but engine still turns over scenario?
Thanks for all the help
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Discussion Starter · #8 ·
So new crank sensor, connector as well as new ignition switch/harness installed. Now I'm dealing with a No Crank issue. Battery became weak from all the testing last week I'm suspecting a bad cell since I'm getting just barely over 12 volts on the multimeter but getting a weak spark. Friend is suspecting a bad ICM. Thoughts?
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So new crank sensor, connector as well as new ignition switch/harness installed. Now I'm dealing with a No Crank issue. Battery became weak from all the testing last week I'm suspecting a bad cell since I'm getting just barely over 12 volts on the multimeter but getting a weak spark. Friend is suspecting a bad ICM. Thoughts?
Weak spark would be the coil or the cap/rotor. Depending on where your testing from. The ICM commands the coil to fire and has nothing to do with the intensity of spark. Test the coil, it should be a nice blue spark and able to jump 1/2".
AC Delco is the brand you want to get if replacing coil or cap/rotor
Dont forget to get a crank relearn after you get everything working. Whenever a crank sensor is removed/replaced it should be done.
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Discussion Starter · #10 ·
Something I can't get past in my head is I'm not getting a 2-3 second fuel pump prime signal. Just a split second of a signal enough to hear the relay click but not stay on. This is making me super suspicious of the ECM. Can you think of any wires and/or sensors I should check that the ECM might rely on before cranking over the engine? It must either be something wrong with the ECM itself or something telling it to not run the fuel pump prime signal. Again, I greatly appreciate your patience, advice and input.
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Discussion Starter · #11 ·
The silence is deafening to my last questions. Maybe I should re-phrase the question. If it's not the ECM, what other possible components could it be?
Also, I'm seeing conflicting information on a few different areas where the ECM requires additional programming even after it is installed on sites where they say they program it to your vin and mileage before sending it to you. I'm worried that I'll go through this process and end up no further than before.
ADDITIONAL VEHICLE SPECIFIC ON-CAR PROGRAMMING MUST BE PERFORMED AFTER INSTALLATION TO PREVENT DRIVABILITY AND STARTING ISSUES
Thanks!
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If you are referring to me. I am not on this site as much. I sold my S10 and my wife just had a baby.
Try unplugging the oil pressure sensing unit, turn the key from OFF to RUN, and see if the pump comes on for 2 seconds and then shuts off.
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Burned is great at this stuff ! Follow his advice 
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Discussion Starter · #14 ·
No burned you're absolutely awesome! I was just hoping anyone out there had any knowledge to lay down regarding ECM troubleshooting other than the ones I find following the wiring diagrams.
Anyways, I finally got a hold of another friend to come over and hook up a second obd II to the truck to see if he had any different results (mine simply wasn't connecting to my tablet so I wasn't sure if it was bad itself since it was a cheap one or pointing to a bad ecm). Results of the real obd II tester is that it could not communicate to the ecm, yay something conclusively tested wrong!
I'm now 99% sure it's the ECM, the other 1% is a bad ground wire or a wire in the harness or something else altogether. So I'll be getting a hold of a used one and have it flashed for the truck to see how it goes.
I'll still check out your latest suggestion for sure burned and for sure and if you'd like provide some input to some other circuits or wiring I can check into and test while waiting for the new module to show I'd certainly appreciate it immensely.
Again, thanks a ton for your help and knowledge!
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Did this get fixed? Was it ecm?
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The MAF shares ground with A/C. Fuel pump grounds at the back on the frame rail drivers side.
When the ignition is initially turned to the RUN position, the PCM activates the fuel pump relay by applying battery voltage through the dark green/white stripe wire for 2 to 3 seconds. If the PCM does not receive data from the crankshaft position sensor during this time, it will deactivate the fuel pump relay. While the relay is activated, battery voltage from ECM B 20 amp fuse is applied to the grey wire that runs directly to the fuel pump.
The fuel pump relay should be activated continuously when the ignition is in the START position.
My truck would crank over fine and run. It would shut off briefly as I was driving. Very scary. There are 4 contacts inside that power different circuits.
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I have a question on my 2000 s10 5 3 swap headlights and taillights com on when switch is on and or truck running but when I apply the brake they both go off plus I'm haven't the same issue with fuel pump not priming but can pull relay and cross it out and it works fine any suggestions could it also be the ignition switch
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When you quote another post, make sure you start below the last [/QUOTE]
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30,918 Posts
I have a question on my 2000 s10 5 3 swap headlights and taillights com on when switch is on and or truck running but when I apply the brake they both go off plus I'm haven't the same issue with fuel pump not priming but can pull relay and cross it out and it works fine any suggestions could it also be the ignition switch
Start your thread in the Lighting/Electrical forum.
BTW, If you're using Talk to Text, or posting from your phone, make sure you include punctuation and check spelling before you post. It makes reading you posts easier.
Thanks.
Source: https://www.s10forum.com/threads/2000-s10-no-start-no-fuel-pump-prime-signal.772722/
Posted by: alfredproming1963oad.blogspot.com
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