2018 Chevy Silverado k3500 fuel signal wiring

Sean Owner Arizona Posted   Latest  
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Driveability
2018 Chevrolet Silverado 3500 HD WT 6.6L (Y L5P) 6-spd (1000)
P228B — Fuel Pressure Regulator "B" - Forced Engine Shutdown
P228C — Fuel Pressure Regulator "A" Exceeded Control Limits - Pressure Too Low
P2635 — Fuel Pump "A" Low Flow/Performance
Customer Complaint Of Low Power Intermittently

Customer dropped off this Silverado 3500 can and chassis with a complaint of low power intermittently. I scanned the pcm, and the current codes are P228B, P228C, and P2635. Identifix shows that all 3 codes are almost always a fuel sender issue. On the datastream, the secondary fuel level shows 1.06 volts, with intermittent spikes to 4.98 volts while. The is actually an access panel in the flatbed right over the sending unit, and I scoped it, but I only read .22 volts on the signal wire, and a square wave 5 volts on the low reference. Data shows 4.98 volts with it unplugged. According to the wiring diagrams, both wires are supposed to go to the fuel pump driver, but the repair info states that cab and chassis is different, but doesn't state what the difference is, or where it is. I tried locating it, and I cannot. What I am trying to do, is scope the signal at the driver, but I need to know if this application even uses one, and if it does, where it is. I would also like a better description of how this circuit is supposed to work with a square wave reference. I have never seen that before.

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Marvin Mechanic
Mississippi
Marvin
 

Is tank wrinkled off straps

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Sean Owner
Arizona
Sean
 

What do you mean by wrinkled? Top of tank is covered in stucco, and I had to chisel it away to get to the sending unit. Bed is loose, and I will look at that once I get it on the hoist to change the oil.

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Marvin Mechanic
Mississippi
Marvin
 

There is a service bulletin about dirt stopping up tank vent and collapsing tank hard enought to bend the sending unit .

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Sean Owner
Arizona
Sean
 

Not collapsing at all. I am more concerned about the square wave on the reference, which I have never heard of.

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Marvin Mechanic
Mississippi
Marvin
 

Is this pump different than most ..most diesels they just run all the time engine is running..have you checked fuel pressure .pump not running at all would or could cause the main common rail pump to not profuse max pressure ..especially if is pulling thru a dead tank pump ..I have not worked on a l5p yet but it’s just a denso instead of bosch

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Justin Educator
California
Justin
 

Any time you get 4.98 Volts on a signal wire that means you either lost the sensor ground or the signal shorted to the 5V ref. It is most likely a pin fit issue with the sensor ground for the fuel sending unit at least.

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Sean Owner
Arizona
Sean
 

I understand that, what I don't understand, is why the scope reads .22 volts, even when the data is acting up, and why there's a square wave reference when al I have ever seen is voltage, or ground that pulls the signal wire down, or up. I am reading .22 volts regardless of whether it's plugged in, or not, back probing, or straight to pin with it unplugged. The pid reads 1.06 unless I am…

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