Fuel Pressure Stuck At 31,000

[Utsuh.]

Hello Everyone, Im new around here and im trying to get a bit of help on my 2013 LML. I bought it not working and im starting to see why they didn't even bother to fix the truck as its been quite a electrical cluster. My main problem right now is the FRP sensor it reads 31,000 PSI (about 210 MPa). I have used back probes on the sensor to get no readings at all on the 5 Volt Reference, same thing for the signal and ground wire. So I assumed that the wires leading to the ECM might be where my short is but when doing a continuity test on the pins for the ECM connector Im still not getting anything. I have done the test with Fuel Pressure Switch unplugged and probing from the switch and I still didn't get anything. Im starting to think that either im doing something wrong or the diagrams im using are wrong.

Everything I did to test the sensor

• Unplugged the connector and read what it shows for the pressure with a scanner still reading 31,000 PSI
• Probed from the FRP connector to the ECM
• Probed from the Fuel Pressure Switch to the ECM (mainly trying to make sure there wasn't a short in the small wiring that lead to the switch)
• Continuity test on all the pins for the FRP didn't get a reading my multimeter just stayed the same using the lowest ohms setting and even tried using my power probe
• Unplugged the ECM and FRP to isolate it to do all of this

 

[2004LB7]

Unplug bothe the ECM connectors and the fuel pressure sensor. Test continuity between all the pins on the sensor side since you know what pins those are. Make sure none show continuity. Then probe a single wire a a time with one end of the meter at the sensor side and the other end at the ECM connector. Make sure each wire is making good continuity. Even when moving the harness and wiggling it around.

Might not be a bad idea to load test each wire with a headlight or turn signal bulb just to rule out a poor connection that shows ok on the metal but fails with any significant current

If all checks ok. Might be a bad ECM

 

[Utsuh.]

Unplug bothe the ECM connectors and the fuel pressure sensor. Test continuity between all the pins on the sensor side since you know what pins those are. Make sure none show continuity. Then probe a single wire a a time with one end of the meter at the sensor side and the other end at the ECM connector. Make sure each wire is making good continuity. Even when moving the harness and wiggling it around.

Might not be a bad idea to load test each wire with a headlight or turn signal bulb just to rule out a poor connection that shows ok on the metal but fails with any significant current

If all checks ok. Might be a bad ECM

So I am able to get power to the switch of the FRP turns out on the fuse box someone broke some pins meant for the #60 Fuse but for some reason i am still not able to get anything pass the switch im still testing and trying to find out what going on with it but its progress right now im still getting 31,000 PSI on my FRP. Im getting my scanner back today so that should help me a tremendous amount once i get it back.

 

[Ron Nielson]

Free Car Service Manuals from Operation CHARM — No strings attached!

Get the manual for your truck so you can understand how the wiring should work

 

[NC-smokinlmm]

It could be the fpr has gone bad.

 

[Ron Nielson]

See the attachment

 

[Utsuh.]

I got my scanner back an was able to scan the truck. I have 2 codes which I believe are going to help me find the culprit of my issues they are p0193 and p2294. While I was waiting to get my scanner back I went ahead and kept looking found some shorts and fixed them now my sensor to my FRP is getting 5v reference, signal wire and low reference wire. I’m still getting the same amount of pressure and for the sake of it I did put some new sensor do the regulator and the FRP just so I have clear of mind of those 2. For the p2294 code I have checked the wire both are somehow getting 3.0 to 3.4v. Might be wrong but I believe one of these wires shouldn’t be getting any voltage.

 

[Utsuh.]

I did a little test i unplugged my FRP and my ECM I checked how much voltage my signal wire was getting and it read 0 as expected but once i plug the ECM back in the voltage goes up to 4.8 - 5.0. My thinking behind this was if I unplug my ECM and still get the same reading something on the harness is making that wire get those voltage, but when I plug in my ECM thats when i get those reading. I just want some clarification on the matter is it by chance my ECM is the culprit on this matter? I fixed my other issue today with the p2294 code someone had pluged the wrong plug in when i was reading a diagram i notice that the colors were meant to be purple/white and yellow the wire plugged in was black and yellow. Swapped those 2 connectors and that code went away so i solved that, so I mainly need help on if my ECM is the issue here.

 

[2004LB7]

Fuel pressure regulators are controlled via PWM. So unless your meter is designed to interpret PWM it's going to give you weird readings

A scope or a duty cycle capable meter is needed to really see what you have on the FPR line

 

[Ron Nielson]

I did a little test i unplugged my FRP

You meant FPR (fuel pressure regulator), right? Or did you mean FPRS Fuel rail pressure sensor? It's difficult to keep all those abbrs straight and everyone on the same page.

 

[Utsuh.]

You meant FPR (fuel pressure regulator), right? Or did you mean FPRS Fuel rail pressure sensor? It's difficult to keep all those abbrs straight and everyone on the same page.

I mean the FPRS (Fuel rail pressure sensor) my regulators are okay now the only code i have at the moment is the p0193 (high voltage signal from the Fuel Rail Pressure (FRP) sensor). Thats reads 4.8 volts KOEO.

 

[2004LB7]

I mean the FPRS (Fuel rail pressure sensor) my regulators are okay now the only code i have at the moment is the p0193 (high voltage signal from the Fuel Rail Pressure (FRP) sensor). Thats reads 4.8 volts KOEO.

With the sensor connector removed?

On the sense wire, 5 volts is 0 psi while 0 volts is 31k psi. So if the sensor is unplugged it will show maximum regardless of the actual pressure.

You can always put a jumper across the connector pins and watch with a scan tool what the fuel pressure reading is. Power to signal. Not the ground unless you are using a potentiometer

 

[Utsuh.]

By sense wire you do mean the signal wire right? I tested it again with the sensor also plugged in just now still reading the same thing with 4.8 but also why would the scanner still be showing 31k psi, if 5v is 0 psi and 0v is 31k?

 

[2004LB7]

Signal - yes

Where are you measuring this 4.8V? Because one line is going to be hot all the time when the ECU is powered up

 

[Utsuh.]

Signal - yes

Where are you measuring this 4.8V? Because one line is going to be hot all the time when the ECU is powered up

The signal wire (YE) has been reading 4.8V while the 5 Volt Reference wire (TN) reads 5v and low reference (OG/BK) is just 0. This is the diagram I was using to figure out which is which.

 

[Utsuh.]

UPDATE: The truck now reads .03-.05 Volts on the yellow signal wire and the issue was the ECM it was getting an internal draw from it but even after this for some reason the p0193 code is still there marking that it was high voltage I have back probe this wire from the fuel rail pressure sensor all the way to the ECM connector and it reads the exact same all the way through. I am not sure how what else it could be I have been trying to run some test and thinking maybe a connecter pin isn't crimped properly maybe allowing for the ECM to ignore the signal wire or the connecter just isn't sitting right. If anyone has any information on this or had something like this go on let me know.