• Home
  • Topic
  • huge stft's, abnormally low O2 sensor voltages. PCM issue?

huge stft's, abnormally low O2 sensor voltages. PCM issue?

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here huge stft's, abnormally low O2 sensor voltages. PCM issue?

This topic contains 1 reply, has 2 voices, and was last updated by Rahul Jones Rahul Jones 1 month, 1 week ago.

  • Creator
  • #1026796
    Mike Lamberti
    Mike Lamberti


    Can anybody just give me some quick insight into this issue with my car. 2014 Malibu LT, 2.5L. When at cruising speeds the car shows very abnormal values for fuel trims and o2 voltages. This also only happens when trying to set the cruise control. It seems to normalize sometimes, only when car is very warm and has been driven a long while prior. This car has an issue too, where after 2nd gear, every upshift comes with a complete lack of power after it. If you release off the accelerator after the shift, then slowly press down, the acceleration comes back, but after the upshift and car just bogs to nothing. I have no exhaust restrictions. I have no vacuum leaks. Fuel pressure on low side ranges from 40-60psi, on high pressure side its good too, pressures upwards of 1500-2000psi when accelerating. I compared scanner snapshots from an old ScannerDanner thread from a while ago to my car’s scanner data, and nothing seems out of the ordinary. When at idle the fuel trims and o2 voltages act as they should. Upstream switches back and forth, downstream remains at about 0.7V.

    At cruising speed (about 50mph):
    stft = +30%
    ltft = +40%
    upstream O2 = 0.025V
    downstream O2 = 0.035V (yes these voltages are typed correctly, they stay this low, and stay stuck there. Sometimes they go into normal operation, but sometimes this happens)

    This car has a P0101 that will never go away. Smoke test shows no leak on intake and plumbing. MAF sensor replaced. Both PCV valves replaced. New GM air filter.

    It runs pretty rough until very very warm, and has the loss of power after shift as stated above. Resetting foot and pushing down resumes decent acceleration.

    So what gives!? The very odd fuel trims and O2 behavior and P0101 that never goes away makes me very confused. So I’m wondering if it’s a computer issue I used to have P0300 and P219A, but those have been gone for a while now.

Viewing 1 replies (of 1 total)
  • Author
  • #1026833
    Rahul Jones
    Rahul Jones

    Have you checked the oxygen sensor condition physically? I have a doubt it is covered in crud. If possible to swap, swap the downstream and upstream then check.

Viewing 1 replies (of 1 total)

You must be logged in to reply to this topic.