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Old 01-16-2018, 11:59 AM   #1 (permalink)
AHGSP
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GM Service Manual Diagnostics for P0088?

Wonder if anyone can provide a link or image of the diagnostics steps to be taken by a tech when the P0088 "High Fuel Rail Pressure" code is set?

Long story short, I threw this code on my 08 3500 Silverado LMM 222k miles while at the farm and after much research and going as far as I could with my lmited tools and knowledge, had narrowed it down to what I believed were either the fuel pressure regulator on the back of the CP3, the fuel pressure sensor, or possibly a kinked fuel line. When recording data on my cheap scan tool, upon startup, my rail pressure would spike to around 31,200 psi and then drop down to about 12-13,000 psi at idle right before it threw code. Research told me it should be around 5000 psi. I don't have a manual fuel pressure tester, nor the ability to call for specific parameters for comparison, but from what I researched, a manual pressure tested should be hooked up to test the supply pressure first to rule out a kinked line after visual inspection, then to compare the rail pressure to what the scan tool was reading to verify the sensor was giving accurate feedback, which would either verify the pressure sensor was good or bad, or the regulator was good or bad.
So off to the dealer it went and from their diagnostics, it was the pressure regulator... they called this morning after 5+ hours of billable labor and waiting 2 weeks for the new thermostats to come in that I had asked they replace, since they already had it open and... it's not the regulator, it's now the sensor... He forced regen on the dpf, because it had apparently coded while they had it and ran it for several hours with no problem yesterday, but when he started it this morn, it threw P0088 again. When asked, he had yet to manually test fuel pressure.

I asked if they were willing to eat the part and labor if it wasn't the Pressure Sensor and they are, but I'd like to see and have the actual step by step diagnostics that SHOULD HAVE been performed.

As an aside, factory fuel filter is deleted and has been replaced several years back with a FASS Titanium when the injectors kicked it and were replaced, but otherwise the truck has zero mods and is a work truck for towing livestock, thus reliability is EXTREMELY important.

Thanks kindly in advance for any help!

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Old 01-16-2018, 07:48 PM   #2 (permalink)
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You have a lift pump?

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Old 01-16-2018, 08:07 PM   #3 (permalink)
diesail
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I believe the rail pressure in 23000 psi. And yes I would suspect the fuel pressure regulator
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Old 01-16-2018, 09:43 PM   #4 (permalink)
Ron Nielson
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From ALLDATADIY:

The problem could be:
Short to ground or high resistance on FPR Solenoid supply voltage or FPR Solenoid control




DTC P0087 or P0088

Diagnostic Instructions


  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection\Initial Inspection and Diagnostic Overview
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
  • Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors

DTC P0087

  • Fuel Rail Pressure (FRP) Too Low
DTC P0088

  • Fuel Rail Pressure (FRP) Too High

Circuit/System Description

The fuel injection pump supplies high pressure fuel to the fuel injection rails, and then to the fuel injectors through high pressure pipes. The fuel rail pressure (FRP) sensor is a three wire sensor mounted in the right fuel injection rail. The FRP sensor uses a 5-volt reference circuit, a signal circuit, and a low reference circuit to monitor fuel rail pressure. This information is sent to the engine control module (ECM) to assist in the fueling of the engine.

Conditions for Running the DTC

P0087
  • DTCs P0090, P0192, P0193 are not set.
  • The engine is running.
P0088

  • DTCs P0087, P0192, P0193 are not set.
  • The engine is running.
Conditions for Setting the DTC

P0087

  • The actual FRP is more than 15 MPa (2,176 psi) below the desired FRP. OR
  • The actual FRP is less than 22.5 MPa (3,263 psi).
P0088

  • The actual FRP is more than 20 MPa (2,900 psi) above the desired FRP. OR
  • The actual FRP is more than 189 MPa (27,412 psi).
Action Taken When the DTC Sets


  • DTCs P0087 and P0088 are Type A DTCs.
  • The ECM commands the engine to operate in the Reduced Engine Power mode.
  • The message center displays Reduced Engine Power.
Conditions for Clearing the MIL/DTC

DTCs P0087 and P0088 are Type A DTCs.

Diagnostic Aids

P0087

  • Water or gasoline contamination of the fuel may cause this DTC to intermittently set. Refer to Contaminants-in-Fuel Diagnosis. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Contaminants-in-Fuel Diagnosis
  • When ambient temperatures are below 0C (32F), the fuel tank pickup screen may be iced over from water in the fuel tank.
  • When power enhancing devices have been attached to the fuel rail pressure sensor circuits, this DTC may set and adversely affect the fuel system components.
  • If the fuel pressure relief valve is not torqued correctly, the valve will leak fuel into the fuel return system causing this DTC to set. The fuel pressure relief valve uses a bite type seal, and proper torque is essential for valve to rail sealing. Refer to Fastener Tightening Specifications.
  • High fuel injector return flow may cause this DTC to set.
  • The addition of fuel system enhancements, such as auxiliary fuel tanks or add on fuel filters may relate to driveability complaints.
P0088

  • This DTC will set if the electric fuel prime pump runs continuously during engine operation (van only). Refer to Fuel Pump Electrical Circuit Diagnosis. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics
  • If the fuel system pressure is actually too high, a fuel knock will exist.
  • A sticking FRP regulator may cause this DTC to set.
Special Tools

CH-48027 Digital Pressure Gage

Circuit/System Verification


  1. With engine running, observe the Actual Fuel Rail Pressure parameter with a scan tool. A normal reading would be approximately 40 MPa (5,802 psi) with the engine cold, and 30 MPa (4,351 psi) at operating temperature.
  2. Engine running, observe the DTC information with a scan tool. DTCs P0087 or P0088 should not set.
  3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing

P0087

  1. If DTC P0090, P0168 or P0191 is also set, refer to Diagnostic Trouble Code (DTC) List - Vehicle. See: Diagnostic Trouble Code Descriptions
  2. Ignition ON for 90 seconds, verify the scan tool FRP Regulator Command parameter is less than 20 percent.
    • If greater than the specified range, replace the ECM.
  1. Attempt to start the engine.
    • If the engine does not start, refer to Engine Cranks but Does Not Run. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Symptom Related Diagnostic Procedures\Engine Cranks But Does Not Run
  1. Install the CH-48027 to the fuel rail service port and slowly increase the engine speed until reaching wide open throttle (WOT).
    • If more than 5 inches Hg of vacuum was present during engine speed increase, replace the fuel filter and inspect the fuel supply lines for damage between the fuel tank and the fuel injection pump.
    • If no restriction was found, test for high fuel return flow.
  1. With the engine idling or at an idle, command the fuel pressure control to 180 MPa (26,106 psi) with a scan tool. Observe the Actual Fuel Rail Pressure parameter. The actual fuel pressure should be the same as the commanded pressure.
    • If the Actual Fuel Rail Pressure is less than 165 MPa (23,931 psi), refer to Fuel System Diagnosis - High Pressure Side. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics
Important: If the fuel temperature is near 121C (250F) during the duplication of the complaint, or in the Failure Records for this DTC, inspect for a restriction in the fuel cooler air flow or the fuel heater always ON. Refer to Fuel Heater Always On. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Symptom Related Diagnostic Procedures\Fuel Heater Always On


  1. Operate the vehicle within the conditions for which the customer complaint occurs while observing the CH-48027. You may also operate the vehicle within the conditions that you observed in the Freeze Frame/Failure Records.
    • If the vacuum was more than 12 inches Hg of vacuum at any time in the operating range, inspect for kinked or restricted fuel supply lines.
  1. Operate the vehicle within the conditions for which the customer complaint occurred. Observe the Actual fuel Rail Pressure and Desired Fuel rail Pressure parameters with a scan tool. Fuel pressures should be the same for both parameters.
    • If the Actual Fuel Rail Pressure is less than the Desired Fuel Rail Pressure, refer to Fuel System Diagnosis - High Pressure Side. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics
    • If fuel system tests normal, refer to Diagnostic Aids.
P0088

  1. Start the engine and operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
  2. Observe the Actual Fuel Pressure parameter with a scan tool. The actual pressure should be 30 MPa (4,352 psi) with the engine idling at operating temperature.
  3. Command the fuel pressure with a scan tool, incrementing through the entire fuel pressure range. The fuel pressure should increment and stabilize through the entire fuel pressure range with actual and desired fuel pressure within 5 MPa (725 psi) of each other.
    • If the pressure difference between the actual and desired pressure are more than 5 MPa (725 psi), test the solenoid supply voltage circuit and the solenoid control circuit for high resistance or a short to ground. If the circuits test normal, replace the FRP regulator.
    • If the pressure difference between the actual and desired pressure is less than 5 MPa (725 psi), refer to Diagnostic Aids.
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Last edited by Ron Nielson; 01-16-2018 at 09:44 PM.
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Old 01-16-2018, 11:16 PM   #5 (permalink)
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Quote:
Originally Posted by G2GBY View Post
You have a lift pump?
Yes, a FASS Titanium 95GPH
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Old 01-16-2018, 11:22 PM   #6 (permalink)
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Quote:
Originally Posted by diesail View Post
I believe the rail pressure in 23000 psi. And yes I would suspect the fuel pressure regulator

FPR replacement didn't fix the issue. He forced regen after replacement yesterday eve, as it must have coded for the dpf on them while there and it didn't throw the P0088 code while they had it going through regen. Left in the shop over night and when he started it this morn, it coded P0088 on him.
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Old 01-17-2018, 12:14 AM   #7 (permalink)
heymccall
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Two things come to mind...
Either the lift pump is supplying more than the designed 8-10 psi, or, since the FPR was replaced, the wiring to it is suspect.
IIRC, higher voltage to achieve lower pressure. Lower voltage to achieve higher pressure.

If it were the rail pressure sensor, it would, most likely, be a different code.

Ron posted this on another thread https://www.dieselplace.com/forum/63-...lmm-p0088.html

Also, from Ron (posted above)
Quote:
If the pressure difference between the actual and desired pressure are more than 5 MPa (725 psi), test the solenoid supply voltage circuit and the solenoid control circuit for high resistance or a short to ground. If the circuits test normal, replace the FRP regulator.
Also of note:
Quote:
P0088

This DTC will set if the electric fuel prime pump runs continuously during engine operation (van only). Refer to Fuel Pump Electrical Circuit Diagnosis. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics
In other words, since it wasn't the FPR, then it has to be wiring or whatever controls it.
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Last edited by heymccall; 01-17-2018 at 12:21 AM.
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Old 01-17-2018, 12:53 PM   #8 (permalink)
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Thank you Ron, I think this is what I need.
As of the moment, if the FRP Sensor doesn't fix the issue, the dealer is going to eat the cost and labor for the sensor. If it fixes it, I have no problem paying for it and will have to see how they intend to handle the replacement or the FPR and 5+ hours labor, to replace a part that wasn't the fault.
When I asked yesterday, as of yet, the tech had not hooked a mechanical pressure test gauge up to the rail test port to verify the rail pressure matches what he's seeing on the scan tool, had not tested supply pressure, nor had he verified any of the wiring.
They are supposed to get it in this afternoon to replace the sensor, so I'm waiting to hear from them.
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Old 01-19-2018, 11:36 PM   #9 (permalink)
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Well they've now replaced the fuel pressure regulator and the fuel pressure sensor with no fix and are now convinced it's the fuel pressure relief valve causing the P0088 high pressure code...
As of yet and though I've mentioned it several times, they have yet to put a mechanical pressure gauge on it, nor ran any reference test on the wiring. They are also apparently unaware how to bottle test the pressure relief bypass and think they can convince me that "process of elimination" is the only way to figure this out.

Oh, and is the Tech not only NOT diesel certified at this Chevy Dealership, nor do they have a Certified Diesel Tech, he is calling a local independent diesel mechanic for over the phone help... "I'd like to use my lifeline call please"...

Any suggestions of a number to call GM Customer Satisfaction?
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Old 01-19-2018, 11:37 PM   #10 (permalink)
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As an aside, they've had my truck since January 2nd.

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