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| 2009 Chevy Silverado plow truck (with apologies for the CCTV-screencap image quality) |
First, a bit of a back story. Electronic fuel injection was just hitting the mainstream when I began working on cars for pay (rather than to avoid paying...) just over 20 years ago. There were several different strategies involved in feeding the systems with fuel, all of which involved at least one electric pump. To prevent the pump from running unnecessarily after a stall, a crash, or just sitting with the key on, the pumps were usually switched on by either the engine computer (through a relay), an oil pressure switch, or both (early GM systems especially).
Most had a single in-tank fuel pump that delivered a constant feed of fuel at a pressure governed by a regulator (usually throttle-body or injector-rail mounted and vacuum controlled) that bled any excess fuel back to the tank through a return line.
Others - most notably the Europeans - would use a low pressure feed pump in or near the tank to supply a second, high pressure pump that ultimately accomplished the same function as the single-pump setup.
The odd vehicle had the ability to vary pump speed, usually through a dropping resistor, or via high frequency voltage toggling (known as pulse-width modulation). This was done primarily to reduce pump noise at low speed and idle, when demand was low and ambient noise less likely to disguise the ruckus.
As technology has introduced more precise injection control, a large number of vehicles have gone to what are called "returnless" systems, where there's no longer a second fuel line coming back from the engine compartment to return excess fuel supply. A single line simply supplies fuel at the required pressure to the injector rail. This eliminates some parts, but most importantly, prevents the fuel from being warmed by engine heat prior to its return to the tank, which apparently offers benefits in emission reductions and possibly even power production.
Often there's a fixed pressure regulator in the tank or a nearby filter/regulator assembly to make this single line system possible. Others vary the fuel pump's power supply to control its output and therefore pressure, usually with feedback from a fuel-rail pressure sensor. This is where our Jackass Award story begins.
An important note: GM is not alone in using the basic design I'm about to discuss. Ford trucks are well know for fuel pump control module failures, for example. But some questionable engineering choices do make the one used on GM's recent model year full-sized pickups - the example featured, the first of these I've encountered, is a 2009 model - Award-worthy.
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| This seemed like a good idea to someone... |
The above photo shows where GM chose to locate the Silverado's (and the identical Sierra's) FPCM (Fuel Pressure Control Module), just above the spare tire beneath the box at the rear of the truck. Ford is equally guilty of mounting the fuel pressure control module where corrosion will eat it. They were doing it well before GM decided to follow suit. Hey, if it didn't work for Ford...
To diagnose this thing, most of the trouble code diagnostic "trees" require you to unplug this connector. The lid swings down to unlatch it - impossible, by about an inch, with the spare tire in place. Ever lowered the spare on a modern pickup?
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| Rube Goldberg would be proud |
I have. Fortunately, this truck , in spite of being used for plowing snow and landscaping, is well-kept, clean, and not a big muddy ball of corrosion, so the process was only slightly aggravating: find and extract the toolkit (often buried or missing), unlock the spare tire lock (good seize-in-place potential), assemble the correct sequence of crank segments (instructions? Who needs 'em?), spend a few minutes trying to get the tool to align and function in the winch (you'd think the built-in guide would make that a first-attempt thing. It doesn't.), crank the spare down.
Finally able to disconnect the connector, we verify that the module has failed and needs to be replaced. Surprise! Our local dealer has one in stock.
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| On the vehicle, this view is only possible with a mirror, a boroscope, or a cameraphone jammed up against the floor of the box. Nice corrosion. |
If you look closely at the spare tire-view photo, you can see that the module is fastened to the bracket it's mounted to from above. A Jackass Award qualifier. Extra Jackass points though because the fasteners in question are rounded-head Torx bolts with fine threads - seen from the top, after mild, fruitless digging out with a pick - in the above photo. The three of those are not coming out without a level of personal attention that's all but impossible in-situ.
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| Another cameraphone-aided view. Only my hand could see this otherwise. Thank goodness for ratcheting wrenches. |
The FPCM is mounted to a large bracket that also holds the TBCM (Trailer Brake Control Module) and another small electrical component. It bolts to the left frame rail and the spare tire winch mount. Fortunately, its three fasteners have conventional hex-heads, though, in true Jackass form, they are also top-mounted, and the winch-side one is conveniently and for no apparent reason located directly beneath the pickup bed's reinforcement beam. There will be no using air tools or even a ratchet on those. Nice. (At least this particular truck was mud and corrosion free.)
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| Voila! |
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| I think I may have peed... |
Once extricated from its bracket, the FPCM peed on our bench. Actually, I was glad to see this, because condemning electrical components can be stressful because you usually can't see anything wrong. Water leaking out? I'm feeling pretty comfortable with my diagnosis! It may need more, but it definitely needs this.
Note that the silver side seen above is the top. The plastic tub forms the bottom, making a decent water-retaining bowl. Obviously the thin layer of sealant wasn't enough to keep the water out (or in). You surely wouldn't want to mount it the other way, and give it a fighting chance.
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| Carefully opened afterward with a 24 oz ball-pein hammer, water can be seen inside. Think those IC chips like water? |
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| The new one has a thick bead of sealant oozing out of it. It got new bolts too, though they didn't come with it. |
So we get our new module, mount it to the bracket, fish the bracket's top-mounted fasteners back in and ratchet-wrench them tight, successfully clear the trouble codes, crank the truck, and get... ...a brief fire-up followed half a second later by a stall and refusal to restart.
Recheck the codes to see what else is wrong, and see..
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| That's not good. |
... that the FPCM needs to be programmed. It's a several hundred dollar box of rocks without the proper software. The common-failing Ford truck fuel pump modules don't need this. They're even available from the aftermarket, plug'n play. Not this one; the final, Jackass Award-clinching move.
Shouldn't have been a surprise, actually, because in this generation of GM pickup, even the power window switches have to be programmed when replaced. Got an identical, same year truck, identically optioned, and want to temporarily swap the switch to put a window up when the original switch breaks on a -25ºC day? Won't work - not programmed to that truck, as one of our tow-truck fleet operators discovered, to his extreme pleasure.
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| Money, money, money... |
At this point there are a couple of options.
- Tow the truck to a dealer (what GM would clearly like you to do, though they'd probably be happier still if their dealer had diagnosed and replaced the module in the first place).
- Tow the truck to a shop that has GM programming capability (which they have to pay to subscribe to - GM is still making a smiley face).
- Program it yourself. Assuming you have the several thousand dollars worth of equipment and/or software to do it, of course. You will also have to pay GM a subscription fee to access the download. $55US gives you 2 days of access to that content, for example, so GM still wins.
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For designing a vehicle that even requires a stand-alone module to operate the fuel pump, then making that module vulnerable to moisture intrusion and mounting where such intrusion is virtually guaranteed (particularly in a vehicle type that frequently gets operated in exaggerated conditions), then making replacement of the module physically difficult by fastening it with corrosion-prone fasteners mounted on the backside of a bracket sandwiched beneath a pickup box (rather than just attaching it from the underside), and ultimately requiring that said module then be programmed for the simple task of running a fuel pump - General Motors, I'm forced to hand you a Jackass Award.
