By on November 10, 2017

Saturn Relay 2007, Image: GM

 

Che writes:

Recently my daughter ran her 2005 Saturn Relay a quart and half low on oil. Alarms started sounding and vehicle shut off. No noises from the engine. I refilled the oil, but it won’t crank. It’s in disabled mode now. I don’t know how to reset it. Any suggestions?

Sajeev answers:

Ever since our last foray into engines saving themselves from catastrophic failure, I’ve always wondered exactly how they “know” not to run without oil.  Turns out it’s a Fuel Pump Oil Pressure Switch, connected downstream from both the fuel pump relay and the oil pressure switch.  Go to 1:06 of this video to see the schematic.

Older vehicles didn’t have “smart” oil pressure switches, to their detriment.  Because we live in a world where people know/care shockingly little about the inner workings of their vehicles.

It’s ironic this question came up, as a friend’s daughter’s Saturn Vue threw a rod (from oil neglect). Or, as she said, “I bricked my car.” That was the moment I insisted she buy a pre-paid service plan on her next ride, and why I remind her mother about said contract every occasion I meet her…but I digress.

Your daughter’s Saturn Relay should test the system as follows:

  1. Make sure the dipstick is reading full.
  2. Disconnect the battery and see if a hard reset will wake up the motor. (hey, worth a shot)
  3. Check the wiring to and from the Fuel Pump Oil Pressure Switch.  If the harness looks weathered, cracked, soaked in oil, fix it.
  4. Get a fuel pressure gauge and make sure there’s enough PSI to run the motor.
  5. What the entire YouTube video above, and you’ll likely replace the fuel pump oil pressure Switch: they are less than $20 online.

Your thoughts, Best and Brightest?

[Image: General Motors]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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21 Comments on “Piston Slap: Relays Have a Fuel Pump Oil Pressure Switch?...”


  • avatar
    Sobro

    I don’t know what qualifies as “older” cars, but I experienced a similar problem in a ’74 Vega. No start condition fixed by changing the oil sending unit after a carb rebuild. What one had to do with the other is a secret for the ages.

    Also fixed a no start condition in a friend’s Escort by resetting the fuel pump shutoff switch located near the rear shock tower. That friend had a tendency to go over speed bumps too quickly, causing the Ford to think it had been in an accident and shut off the electric fuel pump.

    • 0 avatar
      Scoutdude

      Yup this is nothing new, GM used it on their early implementations of electric fuel pumps, including the Vega and Monza. Ford did it too as my 83 F350 had it.

      It was pretty annoying on the old Ford as there was no crank bypass, so when the truck sat for a long period of time, like my trucks tend to do, it would be a exercise in draining the battery. You have to crank and crank and crank until the oil pressure got high enough to close the switch and fill up the carb.

      • 0 avatar
        dukeisduke

        People like to rag on Vegas, but they had some good ideas built in, like wiring the electric fuel pump through the oil pressure sender. My second one (’76 GT, with 93,000 miles on the clock when I bought it) was a little slow to build oil pressure when cold. So the normal routine was: crank the car, it starts, low oil pressure shuts off the fuel pump, car shuts down, then restart and take off.

        The other idea came along with the ’75 models: the coolant level sender and warning light.

        • 0 avatar
          golden2husky

          As Scoutdude says, GM has done this for years. I know W bodies have it as well. It is a good idea as there are plenty of people who feel getting home and driving 10 miles with the oil light on is ok.

  • avatar
    V16

    I’ve always wondered what percentage of drivers have never popped the hood, let alone check the oil level?
    Neglect, translates to big money repairs.

    • 0 avatar
      ajla

      I’ve had two people start crying over the phone when I asked them to open their hoods.

      • 0 avatar
        PrincipalDan

        lol… I live across the street from a small local health clinic and if I had a dime for the number of times I saw some helpless individual (usually of the fairer sex) hopelessly cranking or attempting to crank a vehicle. I’d be making at least a dime a week. ;-)

        I’ve helped a few of them too when I could (jump start etc.)

        Most of them don’t know the hood release from the brake release.

        • 0 avatar
          JMII

          “Most of them don’t know the hood release from the brake release”

          I doubt some people even know those TWO things even exist to chose from!

          My wife, who drove a manual until recently, had no idea how to get her hood open. She knew I reached under the dash to release it, but the lever eluded her. She was looking for a button or switch.

          • 0 avatar
            golden2husky

            Not all women are like that. My wife told me once that she felt that her car was developing a misfire. A week later the check engine light came on indication a misfire on one cylinder. Marry well!

      • 0 avatar
        dukeisduke

        Wow.

      • 0 avatar
        FreedMike

        Dat sensitivity, though…

    • 0 avatar
      indi500fan

      I remember back in the late 60s driving company pool cars that had Dymo labels on the dash near the fuel gauge “check engine oil each fillup” also on the inside of the fuel filler door.

      I’ve had a decades long habit of doing underhood checks on my fleet each Saturday morning.

  • avatar
    pwrwrench

    Yep no oil pressure = no fuel pressure on many vehicles. Glad someone recalled the Vega.
    When this became more common some two decades ago I read that BMW had a similar system, but with an oil level sensor.
    I thought of what would likely happen if one got towed to the service department because of a no-start.
    “YOU MEAN TO TELL ME MY BMW WOULD NOT START BECAUSE IT WAS A QUART LOW ON OIL! I’M LATE FOR A MEETING! I’M GONNA SUE!”

    • 0 avatar
      dukeisduke

      My ’76 never burned much oil, but it leaked a helluva lot, through the rear main seal (rope seal), and the oil pan (the Vega had a windage tray sandwiched between the block and the pan, and used *two* gaskets). I checked the oil frequently, as I was a adding a quart every 600 to 800 miles. If I turned a corner quickly and the oil pressure light blinked on then off, I knew it was time to add a quart. I sold the car with 218k on it, and it still used the same amount of oil, and didn’t smoke.

      Vega engines were stupid bulletproof (especially the ’76-’77 engines with the revised head design with hydraulic lifters), as long as you never let them overheat.

    • 0 avatar
      NormSV650

      Let me tell about my then girl freind, now wife, and her 2012 Forester 2.5l that was almost 2 quarts low with no warnings. Cold start piston slap, puff of blue smoke, coolant loss….needless tk say our Subaru class action letter came after most of my synthetic reserves were depleted, Forester traded on a GMC Terrain, and no receipts to prove I had put many quarts in it.

  • avatar
    Art Vandelay

    On a couple of occasions I have helped people fix a vehicle that was run out of oil and shut itself down. Typically it was as easy as removing the engine from the vehicle and replacing it with a new one.

  • avatar
    oldworntruck

    Seems Sajeev didn’t read the question correctly.
    The post said it will not crank. That problem has nothing to do with fuel pressure.
    Personally I’d use a socket on a breaker bar on the engine crank pulley to make sure it isn’t seized.
    Or if that’s too much work I’d get someone to hold the key in the start position and look at the starter to see if smoke is coming out of it while it tries to spin an engine that is seized.
    If the crankshaft spins smoothly with a socket on it then the no crank isn’t related to running low on oil.
    These vehicles have no starter interrupt for oil pressure.
    Only fuel interrupt.


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