The Toyota Fuel Pump Control ECU Function
Our Best Hotline Calls
From time to time, we have our hotline technicians tell us about their trickiest or most memorable diagnostic problems for which they’ve received calls. This one comes to us from Joe Masterman and his call about a Toyota Fuel Pump Control ECU.
2008 Toyota Tundra 5.7 V8
Assumption has been a humbling thing for me to try to rid myself of (we all know what happens when we assume something). I don’t know about the rest of you, but I sometimes catch myself slipping into complacency. When I was still working at a dealer, we had some DTCs that we didn’t consider “hood poppers.” If you had a P1009 in an Accord, that wasn’t a hood popper—you just quoted a timing chain. It wasn’t worth taking the valve cover off to check the cam timing. Every now and then I would get paddled by a car, my complacency would be punished, and it turned out the timing chain was not the problem. I tried to keep myself sharp, but usually, a whooping from a problem car was just what the doctor ordered when I got lax.
Such was the case when I first encountered a Toyota with a Fuel Pump Control ECU. A lot of people call into Identifix on Toyota vehicles thinking they have a fuel pump problem, but they’re actually confused about how the circuit works. There’s the misconception that the fuel pump should prime for 2 seconds when really the Engine Control Module (ECM) only controls the fuel pump relay (C/OPN Relay) after it sees cranking RPM. I got used to saying “no, check it again when cranking,” and usually the fuel pump was working, or there was another issue such as a bad crank sensor signal.
I about spit out my coffee when someone told me that on this particular Toyota, the C/OPN relay was grounded constant by the ECM KOEO. Rather than argue with him, or assume he was wrong, I considered that this might just be another sign from the Automotive Gods to stifle my complacency and look harder. I dug around the diagrams and sure enough, this was a whole other animal. It had something I had never seen on a Toyota: A Fuel Pump Control ECU.
Have a look at the diagram. I cleaned it up in Photoshop to make it legible. You’re welcome.
You can also view these in Direct-Hit. Looks like a pretty simple circuit, a nice redundant relay setup before the Fuel Pump Control ECU can get power. But hey, that’s Toyota for you. I told the caller, “listen, if the C/OPN Relay is being controlled as you say, there should be power to the Fuel Pump Control ECU all the time on connector A pin 4, Black/White wire. There should be a ground on A3, White/Black. Check it out.”
By the way, Toyota will always show two names for its connectors. In the service manual, you can see the note by the Fuel Pump Control ECU on the diagram that connector A is also called R7.
This ECU is conveniently located—and I mean that sincerely—right above the left rear tire. It has a 4-wire plug and a 2-wire. The 4-wire plug is your power, ground, and control wires; 2-wire plug is the output to the actual fuel pump.
The caller responded “yep, good power and good ground. What’s next, boss?”
I didn’t like the literature on the two wires going from the Fuel Pump Control ECU to the ECM. The pin chart showed 0-3v on one wire, and less than 1.5v on another. Sounded like boilerplate engineering to me.
So instead I had him jump power and ground to the fuel pump itself from connector B. “Power up B1 Blue and ground B2 Red. That pump should start to run and the engine should start” I said. Voila, pump and engine start.
But I needed to know what the other two wires were for, or else we’d basically be flipping a coin. “Heads for ECM, tails for Fuel Pump Control ECU!” I tell him to sit tight. I needed to find another Tundra to probe on.
Luckily for me, we have one at the office and it’s driven by a guy who doesn’t know my reputation for ruining radios (that’s a whole other article, I think I’m going to call it “Automotive Munchausen by Proxy”). I popped the sucker up on the hoist, and I reaped some lovely information with my favorite weapon, the Pico scope.
See what happened when I set my scope up with my Blue lead on pin A2, the DI wire; Red lead on A1, the FPC wire.
While running, the DI line hung out at 10v and the FPC line got a 10v duty cycle. That’s my Fuel Pump Control wire. DI was still a bit of a mystery, as it didn’t seem to do a whole lot.
Let’s look at KOEO this time. I put my Green lead on the power source from the C/OPN relay—I would be remiss to assume the tech on the phone was testing it properly.
Sure enough, it appears the ECM grounds the C/OPN relay all the time KOEO. I saw a 10v blip on the DI line when the key was turned on, but otherwise, it remained at ground. I guess the spec of 0-3v really ought to have said .1v or less.
Let’s crank it up and see what happens!
I saw my 10v blip on the DI, 0v on the FPC, and my consistent 12v from the C/OPN relay. As I turned the key to crank the engine, I saw the DI and the FPC lines both hop up to 10v. The pump must have been running full bore during crank—my theory is that 10v solid on the FPC was my max command. DI appeared to be just for keeping the pump from running KOEO. If they were smart, they’d use it to keep the pump from running during an immobilizer event as well.
Have another look at the waveform with some notes on it.
After all this, I felt confident enough to start playing with it. I removed the DI and FPC lines from the Fuel Pump Control ECU connector and this time when I turned the key, the fuel pump ran all the time. I checked the pins on the Fuel Pump Control ECU where the wires used to be: 10v on both. To the Fuel Pump Control ECU we cranked the engine and the ECM asked for full power to the fuel pump. If I grounded those pins, the pump stopped running.
Here’s a zoomed-in diagram for the Fuel Pump Control ECU. Print this out and hang it up on your box or keep it saved in Direct-Hit in case you ever have one of these cars in your bay.
With this new knowledge, I called my tech back and had him remove the DI and FPC lines. The fuel pump still did not run, condemning the Fuel Pump Control ECU. He thought I was a wizard but I knew better.
Keep on trucking ladies and gentlemen, never stop learning, and never be complacent!
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