Piston Slap: Relays Have a Fuel Pump Oil Pressure Switch?

Sajeev Mehta
by Sajeev Mehta
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 sajeev@thetruthaboutcars.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.
Sajeev Mehta
Sajeev Mehta

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  • Art Vandelay Art Vandelay on Nov 10, 2017

    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.

    • Sgeffe Sgeffe on Nov 12, 2017

      Along with the hood or fender replaced after a rod punches through on its way into orbit!

  • Oldworntruck Oldworntruck on Nov 10, 2017

    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.

    • See 2 previous
    • Whittaker Whittaker on Nov 13, 2017

      @Eddy Currents "Can you come jump me? The car won't start" "Is it cranking?" "Yes, very cranky" "I mean is it turning over?" "Yes but it won't start" "What's the gas gauge say?" "Oh shit, its on empty" "I'll bring some gas" "Shouldn't we try jumping it first"

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