2008 Yukon FSCM VS Fuel Pump

[crows_camaro]

Please advise...

 

I have a 2008 Yukon Denali with a 6.2 engine. The fuel pump is not coming on. I have done some research into the fuel control module (fuel system control module/ fuel pump driver) and discovered that it regulates the fuel pump based on voltage. I checked the voltage at the pump and it is 6 volts when the key is turned forward. If 12 volts is placed to the pump then the pump works and the vehicle cranks and drives. I have spoken with one GM service adviser that stated there should be 12 volts going to the pump to operate and that my Fuel module is the problem. I tried calling a place that specialized in flashing fuel control modules and they were unable to verify. I spoke with another GM service adviser that seemed to actually be looking up in the system and said that the voltage range on a fuel control module is from 6-11 volts. This would indicate to me that the FSCM is functioning properly but the fuel pump itself is not cutting on at the lower voltage. The only tech advise I am reading online is referring to using a test light (not as accurate as voltmeter) and a scan tool to tell fuel pump to cut on and off.

 

Now that I have a switch ran to the pump temporary here are the DTC codes that are appearing.

P2635 - Fuel pump A low flow

P023F -Fuel pump secondary circuit open

P0232 -Fuel pump secondary circuit high

P025A -Fuel pump module control circuit open

P069E -Fuel pump Module request light

P1175 -Fuel trim bank 2

I don't mind replacing the pump myself or taking the FSCM to dealer to be properly programmed to the vehicle but am trying to avoid doing one and still needing the other because I replaced the wrong thing.

Can you advise on what the actual specs are for the fuel pump to operate? Do you know the best way to diagnose this issue?

Thank you for all your help in advance. I don't want to burn the pump up by sending too many volts so I need to fix ASAP,

Joey

[Justin101714]

First, you need to actually find out if it is getting the proper voltage. The ignition 1 signal is going to change by the time you turn on the key and get back there to check it. The way you do this properly is to have someone available to command the pump on and off while having a test light in terminals "A" and "D" at the fuel pump. If the light doesn't illuminate, check for short to ground on either of those circuits. If the circuit tests normal, then replace the fuel pump control module. The voltage is going to vary. You just have to test it before it does start to vary. When the pump is commanded on with a scan tool is when there should be enough to light a test lamp rated for 12V. You can try having someone turn the key on but be right at the connector ready with the test light when they do turn it on.

 

 

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[crows_camaro]

I had my wife turn the key while I had a voltage meter on the fuel pump plug.

I lowered the tank and removed plug directly from fuel pump module. I placed the volt meter prongs on the grey positive wire terminal and the ground (cant remember the color) and the output was 5.91 volts when the key was turned on. the voltage did fluctuate slightly after a few seconds. She turned the key off and we did it again with same/similar results.

 

So am I understanding that since 5.91 volts is at the pump then the pump itself is bad. 5.91 volts is very close to what I was told the voltage range should be.

[Jsdirt]

The fuel pump is pulse-width modulated based on inputs - in other words, it regulates the speed of the pump based on fuel pressure readings from the sensor(s).

 

Any voltage measurement will be an average voltage when tested with a regular multimeter - you need a scope to accurately read the signal.

 

That said, if you're reading close to 6, it's probably getting the proper voltage ... but you won't know for sure without seeing it on a scope.

 

If the FPCM was replaced, it needs to be programmed, or it will not work.

[newdude]

Did you get those codes after bypassing to run the pump on a switch? Are the codes current or history?

 

Looking at the data charts for what the FPFCM, desired fuel pressure is 44.5psi, fuel tank pressure sensor desired voltage is 2-3v, and trim, Ign 1 signal, and pump signal command are all labeled as "varies" so GM does not list any specific range for those voltages.

 

Fuel Pump Flow Control Module (FPCM) – LMF

The fuel pump flow control module (FPCM) is a serviceable GMLAN module. The FPCM receives the desired fuel pressure message from the engine control module (ECM) and controls the fuel pump located within the fuel tank to achieve the desired fuel pressure. The FPCM sends a 25 KHZ PWM signal to the fuel pump, and pump speed is changed by varying the duty cycle of this signal. Maximum current supplied to the fuel pump is 15 amps. A liquid fuel pressure sensor provides fuel pressure feedback to the FPCM.

 

[crows_camaro]

Yes these codes are after the switch was installed. I suspect this is the reason for the P0232.

Earlier in the week the vehicle died but cranked back up and the present codes on that day were

 

P0606 -ECM

P025A -Fuel pump module control circuit open

P069E -Fuel pump Module request light

P1175 -Fuel trim bank 2

P0496 -

P0455 -

P0442 -

P0496 -

The last 4 are evap codes that I believe to point towards the evap purge selenoid that I have not replaced yet but has been an issue for a while with no adverse symptoms.

Also thank you everyone for responding