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"

  • Redapple2 jeffbut they dont want to ... their pick up is 4th behind ford/ram, Toyota. GM has the Best engineers in the world. More truck profit than the other 3. Silverado + Sierra+ Tahoe + Yukon sales = 2x ford total @ $15,000 profit per. Tons o $ to invest in the BEST truck. No. They make crap. Garbage. Evil gm Vampire
  • Rishabh Ive actually seen the one unit you mentioned, driving around in gurugram once. And thats why i got curious to know more about how many they sold. Seems like i saw the only one!
  • Amy I owned this exact car from 16 until 19 (1990 to 1993) I miss this car immensely and am on the search to own it again, although it looks like my search may be in vane. It was affectionatly dubbed, " The Dragon Wagon," and hauled many a teenager around the city of Charlotte, NC. For me, it was dependable and trustworthy. I was able to do much of the maintenance myself until I was struck by lightning and a month later the battery exploded. My parents did have the entire electrical system redone and he was back to new. I hope to find one in the near future and make it my every day driver. I'm a dreamer.
  • Jeff Overall I prefer the 59 GM cars to the 58s because of less chrome but I have a new appreciation of the 58 Cadillac Eldorados after reading this series. I use to not like the 58 Eldorados but I now don't mind them. Overall I prefer the 55-57s GMs over most of the 58-60s GMs. For the most part I like the 61 GMs. Chryslers I like the 57 and 58s. Fords I liked the 55 thru 57s but the 58s and 59s not as much with the exception of Mercury which I for the most part like all those. As the 60s progressed the tail fins started to go away and the amount of chrome was reduced. More understated.
  • Theflyersfan Nissan could have the best auto lineup of any carmaker (they don't), but until they improve one major issue, the best cars out there won't matter. That is the dealership experience. Year after year in multiple customer service surveys from groups like JD Power and CR, Nissan frequency scrapes the bottom. Personally, I really like the never seen new Z, but after having several truly awful Nissan dealer experiences, my shadow will never darken a Nissan showroom. I'm painting with broad strokes here, but maybe it is so ingrained in their culture to try to take advantage of people who might not be savvy enough in the buying experience that they by default treat everyone like idiots and saps. All of this has to be frustrating to Nissan HQ as they are improving their lineup but their dealers drag them down.
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