Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Fuel economy dropped by 80%

2008 Buick Lacrosse Super has check engine light on for oil pressure sensor/switch… Immediately after it started burning gas 3x as fast as my 1999 Tahoe. Outside of oil change and replacing the sensor what could cause it to burn gas so bad? The tires seem fine and no other on the computer.


Is there a question here??

Would a bad oil pressure sensor/switch cause a car to burn through gas 3x faster than normal?
I fill the tank with $35 of regular and it’ll last 2 weeks, so far I’ve spent over $60 on gas this week alone.

No a bad oil pressure switch will not cause a change in mileage. Is there a check engine light on?

1 Like

Yes but when my mechanic read it only the switch was listed.

What code did he read? list it here and you will get more specific information. It (or they) will be in the form of P1234.

Or you can type the code into google, together with “buick” to get more info.

Read what? The diagnostic codes? Did he get a P0520 or a P0522 code?

If that’s all he read, the sensor could be bad and it has no effect on mileage. Change it but test the actual oil pressure first with a mechanical gauge to insure the oil system is OK. If the oil pressure isn’t high enough, it could mean the engine’s oil pressure system is failing and the fuel mileage drop you see is due to the engine destroying itself internally. And you will need a new engine. But that usually throws a red low oil pressure light on the dash.

1 Like

I dont know what codes it had, my mechanic did all that and I never asked what the codes were.

I answered your eventual questions. It is in your mechanic’s hands if you chose to have them work on the car. Good luck with the repair, I hope its not a new engine.


Just because your mechanic read one code doesn’t mean it didn’t throw more codes after you left the shop. That is one problem with driving around with a check engine light that was say for a minor evaporative system leak. You don’t get alerted to something serious.

1 Like

My fear here is that the oil pressure switch is working exactly as it should…
and the engine is running or has been run on empty (oil wise). If it’s the latter, that loss in mileage and the oil burning may be symptoms of damage to the cylinders due to assuming the warning light is malfunctioning when in reality it’s giving you the warning it’s designed to.

Have you checked your oil?
Has the engine run low on oil in the past?
Do you regularly monitor your oil level or just rely on the warning light to tell you when it’s low?

Some engine codes can trip an ECM into a ‘safe’ mode or ‘limp’ mode. In this mode, the computer will purposely stop running the engine at it’s most efficient and use a preservation scenario designed to prevent damage to the engine. If it did trip into a ‘safe’ mode, losing 20% fuel efficiency is not uncommon. I cannot confirm this, because I still don’t have a code to work with.

Limp Home mode with low oil pressure seems more like a self-destruction sequence. Loss of coolant is bad. Loss of oil pressure is catastrophic!

1 Like

You’re assuming that is the problem. No code, so it’s all a guess.

Until/unless that OP answers some of the questions, guessing is all we can do. Hopefully some of the guesses will prompt the OP to think about them and consider their importance in keeping a healthy engine. And perhaps in his/her failure scenario.

As posted above, a malfunction in the oil pressure sender wouldn’t be a cause for loss of mpg. Most common causes of mpg degradation without any associated diagnostic codes present are

  • failed thermostat, causing engine to run too cool
  • failed engine coolant temp sensor, causing engine to run too rich
  • some sensor or wire not hooked up where it should be

Serious problems, but not common, that could cause it are things like loss of engine compression, plugged cat, malfunctioning fuel injectors, fuel pressure regulator, etc. But those would usually cause pretty noticeably drivability problems too. Stalling at idle, poor acceleration, overheating, etc.

One thing you could do yourself maybe, if you can find the fuel pressure regulator. If there’s a vacuum hose connected to it, remove that hose. If any gasoline drips out, it has failed and needs to be replaced. Not every engine uses this type of bolt on fuel pressure regulator in the engine compartment, so this may not apply in your case.

1 Like