2007 XC70 Fuel pump fuse repeatedly blows

[RickHaleParker]

Any ideas? I'll run through the VIDA diagnostics for the fuel pump code (CEM 3F90).

CEM-3F90 Fuel pump relay. Open-circuit or short-circuit to ground

Did you turn the key on with the fuel pump disconnected or the harness fully seated?
Did you apply any external voltage to fuel pump?

[mtd240]

Any ideas? I'll run through the VIDA diagnostics for the fuel pump code (CEM 3F90).

CEM-3F90 Fuel pump relay. Open-circuit or short-circuit to ground

Did you turn the key on with the fuel pump disconnected or the harness fully seated?
Did you apply any external voltage to fuel pump?

Only ever turned the ignition on with the fuel pump harness fully seated. Didn’t bench test the pump; didn’t want to risk excessive wear from it running dry.

[RickHaleParker]

Did you replace the blowen fuse before you turned the key?

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372: CEM-3F90 Fuel pump relay. Open-circuit or short-circuit to ground

Diagnostic trouble code (DTC) information CEM-3F90

M2303365 Condition
Central electronic module (CEM) checks the fuel pump relay, and activates it, when an approved check has been made by the system for Immobilizer. The fuel pump relay is located internally in the Central electronic module (CEM). The fuel pump relay sends voltage feed to the fuel pump when the relay is activated.

If Central electronic module (CEM) detects that the voltage on the output to the fuel pump is too low, the diagnostic trouble code is generated.

The diagnostic trouble code (DTC) can be diagnosed when the fuel pump is activated.

Note! When troubleshooting, the fuel pump may not be supplied with voltage by an external power source without first disconnecting the connector to the Central electronic module (CEM). If the connector is not loosened and the fuel pump is supplied with voltage, this can lead to failure of an internal ground conductor in the Central electronic module (CEM). In turn, this can lead to a number of other malfunctions in the vehicle and that Central electronic module (CEM) must be replaced.

The following applies to vehicles with fuel pump module (PEM):
Central electronic module (CEM) checks the voltage feed to the fuel pump module. The Central electronic module (CEM) activates the voltage supply to the fuel pump control module after the checks carried out by the function for the immobilizer have been approved.

If Central electronic module (CEM) detects that the voltage on the output to the fuel pump module (PEM) is too low, the diagnostic trouble code is generated.

The diagnostic trouble code (DTC) can be diagnosed when the fuel pump is activated.

Substitute value
None.

Possible source

• Damaged power supply fuse.
  Open circuit on cables for voltage feed between fuse box engine compartment and Central electronic module (CEM).
  The cable for voltage feed between Central electronic module (CEM) and fuel pump module (PEM)/fuel pump is short-circuited to ground.

Fault symptoms
The engine does not start.

[jonesg]

Any ideas? I'll run through the VIDA diagnostics for the fuel pump code (CEM 3F90).

CEM-3F90 Fuel pump relay. Open-circuit or short-circuit to ground

Did you turn the key on with the fuel pump disconnected or the harness fully seated?
Did you apply any external voltage to fuel pump?

Only ever turned the ignition on with the fuel pump harness fully seated. Didn’t bench test the pump; didn’t want to risk excessive wear from it running dry.

My pump ran but fuel pressure was not quite high enough to fire engine. Bench test wouldn't show fuel pressure.

I pulled the pump module and opened the pump, crispy brushes with burnt wires. Twisted springs on brushes, it was toast. It was obvious before I pried the pump/motor open that it was shot.

[mtd240]

I had about 20 minutes with the car today.

Checked the battery - 12.3V (due to some cranking yesterday - just wanted to make sure it didn't drain more)
Checked the fuel pump fuse - not blown.
Tried to start the car - lots of cranking, no starting. Fuel pressure didn't even register on the gauge
Hooked up VIDA. It had several codes - Electric fan (ECM-650B), RPM sensor (ECM-5000), and fuel level sensor (CEM-4A33).
Wiggled the RPM sensor wire and erased all the codes
Re-read codes - nothing.
Car still doesn't start. It catches a little bit, but doesn't start.

I am still learning how to use VIDA (is there an instruction guide on its capabilities somewhere?). I tracked the fuel pump relay (CEM output) while cranking - "deactivated" while not cranking, "activated" while cranking. Then I started trying to track the fuel pressure and . . . I had to go pick up my wife. Before closing the hood, I depressed the fuel rail schrader valve and fuel sprayed out pretty strongly.

Any further tips on how I can use this to diagnose the problem would be great! I honestly have no idea why there are no codes now. It seems like fuel pump operation is inconsistent (incl. the fuel level sender).

[RickHaleParker]

I honestly have no idea why there are no codes now.

You cleared out artifacts.

OBD does not clear codes if a problem goes away. Inactive Codes can be used to diagnose intermittent problems. Sometimes they are just hiccups, management systems and OBD is not perfect.

[mtd240]

I honestly have no idea why there are no codes now.

You cleared out artifacts.

Haha right, I mean I don't know why the car isn't throwing a code due to the no-start

[RickHaleParker]

If it is trying to start, your getting Air, Fuel and ignition but not in harmony ... try to get it started in limp mode, disconnect the MAF sensor.

[abscate]

Get that fuel gauge on and confirm 50 psi at rail.

Your car is still talking to you, it just isn't speaking OBD



You usually don't get codes on a no-start. You certainly won't get meaningful ECM codes unless the engine is running fairly well - misfire codes, for instance , are inaccurate if the engine is rough.

[mtd240]

Get that fuel gauge on and confirm 50 psi at rail.

Your car is still talking to you, it just isn't speaking OBD



You usually don't get codes on a no-start. You certainly won't get meaningful ECM codes unless the engine is running fairly well - misfire codes, for instance , are inaccurate if the engine is rough.

Took some PTO at work to hopefully figure this out today.

Battery voltage was 11.3V when I got there today.
Fuel pressure didn't even register on the gauge when in ignition Pos II, or when cranking.
Voltage between pins 2 and 3 on the PEM feed was the same as the battery (I presume that means the CEM is working - telling the PEM to get fuel).
There is some odd behavior though - the fuel gauge works when I first turn on the car, but drops out after a few seconds (or right when I push the brake pedal down - assuming that is due to the battery not holding voltage).

Regardless, the battery is definitely having issues. Not sure I trust Advance Auto's tester (even though I thought Midtronics was a pretty good tester brand). I am going to grab a new battery. This one drops to 6V when I crank now.

Will keep you all updated on the progress. The next step is to pull the rear seat back out and take a look at the pump wiring.