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It will crank, but will not start?

Tiny
KKIRKMAN12
  • MEMBER
  • 2007 GMC YUKON
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 220,000 MILES
My vehicle listed above XL model 1500 will crank but won’t start. We’ve changed the fuel pump, ECM, crank shaft, camshaft, throttle pedal sensor, throttle body sensor, MAP sensor, injectors and fuel rail. Spark plugs are good. It doesn’t have a fuel regulator, fuel module or fuel filter. There's a fuel module and fuel filter on the pump but no on the body or anywhere else. It has half a tank of gas so it’s not out of gas. All fuses and relays have been checked and are good. Battery is good. Still gives codes stating the engine is hot reduce power and turn off AC. We are at a loss as to why it won’t start. It will start then die with starting fluid but that is it. It has compression, spark and fuel but still won’t start. What else could we check or what could the problem be?
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Saturday, October 26th, 2024 AT 12:13 PM

20 Replies

Tiny
AL514
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Hello, exactly what codes are setting? What's the numbers? If the ECT is skewed or one of its wires is shorted to a power wire and the ECM is seeing an extremely high temperature due to the sensor data, but we need the code numbers so we can look up that code criteria.
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Sunday, October 27th, 2024 AT 11:57 AM
Tiny
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Service info states the Cluster will display a Reduced Engine Power message due to high temperatures when the PCM is seeing a temperature reading of 270f, way above operating temperature. If you have a scan tool, check the live engine data with the key On, and see what the Engine Coolant Temperature sensor is reading.

But post all the codes that are set so we can look up their setting criteria. This would be an interesting case study as well.
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Sunday, October 27th, 2024 AT 12:03 PM
Tiny
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But post all the codes that are setting so we can look up their setting criteria. This would be an interesting case study as well.
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Sunday, October 27th, 2024 AT 12:06 PM
Tiny
KKIRKMAN12
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Here’s what it says, along with a video that shows what it sounds like. It gives the throttle pedal code, but it’s already been replaced and the throttle body sensor as well. So not sure why it still throws that code.
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Sunday, October 27th, 2024 AT 12:53 PM
Tiny
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And you are getting the "Engine Hot- Reduced Power Mode" message on the dash I assume?
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Sunday, October 27th, 2024 AT 2:15 PM
Tiny
KKIRKMAN12
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It gives code for everything that has been replaced already. So, I am not sure what else to do or what else it could be. I reran the codes, and this is what it gives me.

List of codes is:
P0107
P0118
P0120
P0122
P0223
P0315
P0443
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Sunday, October 27th, 2024 AT 2:17 PM
Tiny
AL514
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Okay, first of all, does your scan tool give you live engine data?
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Sunday, October 27th, 2024 AT 2:18 PM
Tiny
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Yes I’m getting that message but when we checked the temperature it was reading cold.
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Sunday, October 27th, 2024 AT 2:21 PM
Tiny
KKIRKMAN12
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No it just the one shown in the picture. It’s just a basic one.
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Sunday, October 27th, 2024 AT 2:21 PM
Tiny
AL514
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Just because you're getting a code for a component does not mean that part is bad, never replace a part without testing the circuits that go to it first. Let me look up all these codes and see if there is any circuit that may be related to each sensor.
But also, this P0118 Coolant temperature high code is probably why you are getting that message, let me get the PCM wiring diagrams together really quick.
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Sunday, October 27th, 2024 AT 2:22 PM
Tiny
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Start here, this the coolant temperature sensor, first check the voltage reading from the wiring harness plug with the sensor unplugged. Key On, you should read 5 volts.
Notice it is a 2-wire sensor, with one yellow wire and the other tan.

https://www.2carpros.com/articles/how-to-use-a-voltmeter
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Sunday, October 27th, 2024 AT 2:28 PM
Tiny
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It reads 3.09 but we’ve replaced it when we changed everything else too, thinking that was part of the problem. We changed it with the crankshaft sensor and still having the same issue.
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Sunday, October 27th, 2024 AT 2:44 PM
Tiny
KKIRKMAN12
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The battery is mostly dead as I’m trying to get a reading with a battery charger on it.
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Sunday, October 27th, 2024 AT 2:45 PM
Tiny
AL514
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The Coolant temperature sensor harness plug reads only 3-volts while unplugged from the sensor? It doesnt matter if you replaced it, Im asking about the wiring going to the sensor, not the sensor itself. With this many codes, you have a wiring or PCM issue.
If you read 3volts on the yellow wire with the sensor unplugged, so its out of the picture completely. That 3 volts should be 5volts, and thats the issue here. Low Reference voltage is also what is probably causing all the other codes as well,
The Crank pos sensor code is because you replaced the sensor but did not do the Crankshaft variation Relearn Procedure, so ignore that for now. The 3-volts is a problem.
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Sunday, October 27th, 2024 AT 2:52 PM
Tiny
AL514
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Well, charge the battery overnight, and we will proceed with testing tomorrow then, but you have a wiring or connector issue happening here. Here are all the OEM diagrams for everything setting a code, but you need to have a fully charged battery and then keep and maintainer on it while testing later so battery voltage doesn't drop off.
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Sunday, October 27th, 2024 AT 2:55 PM
Tiny
KKIRKMAN12
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So, am I supposed to test the harness that is unplugged from the sensor or the sensor itself? I did the sensor that is on the motor not the harness and that read 3V.
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Sunday, October 27th, 2024 AT 2:56 PM
Tiny
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Yes, unplugged and check the ECT not the TPS right now but let the battery charge overnight or the readings are going to be incorrect, and the testing will not give accurate results, I'll help you test the harness and these sensors tomorrow, so we have time to go over them correctly. Check the PCM connectors for any green corrosion inside the connector pins on the harness side.
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Sunday, October 27th, 2024 AT 3:30 PM
Tiny
KKIRKMAN12
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Okay
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Sunday, October 27th, 2024 AT 3:38 PM
Tiny
KEN L
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AL514 is one of out best! Please let us know how it goes.
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Tuesday, October 29th, 2024 AT 9:14 AM
Tiny
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Any change on the 3volt reading?
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Tuesday, October 29th, 2024 AT 12:10 PM

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