P1151, idling low then dies.

Discussion in 'SN95 V6 Mustang Tech' started by cughter, Jan 9, 2013.

  1. Hello StangNet,

    I'm posting this thread because I've gotten great advice from some of the mustang experts/enthusiasts on this site before and it's a great community comprised of many knowledgeable contributors.

    I'm working with a 3.8L 02' stang, and I just pulled a P1151.
    I've been driving with that code for about 300 miles with no problems, thinking it was a minor exhaust problem until the other day when the engine died on me while driving (not overheating or anything). When I started it back up it would seem to be running fine when I opened the throttle, but when I let it idle it would fall below the default idle RPM's and die. This led me to believe it might have to do with the MAF sensor. However, the code is suggesting that it has to do with the O2 sensor(s) and that the engine is running rich or lean?

    Before I spend money on this problem I came here to consult you guys for advice I couldn't find by searching through the forum.

    (1) Could P1151 possibly come up with a MAF sensor problem?
    (2) Would cleaning the MAF sensor with MAF cleaner help the problem at all?
    (3) Is there any way to tell if the MAF sensor is bad?
    (4) If this P1151 code has to do with a faulty O2 sensor, will I be able to simply switch around the (4?) O2 sensors in order to find out which one I need to replace?
    (5) If this has to do with a shattered pre-cat or mid-cat on the mid-pipe is there a good way of telling which one needs replaced? (i.e. removing the mid-pipe and shooting a compressor through it to hear if it rattles, or knocking on it to hear if it rattles)

    Besides that, I must have put on my thermostat gasket incorrectly and it's leaking out pretty bad. (Not sure if that would have anything to do with it.


    Thanks in advance,
  2. P1151 relates to O2 sensor Bank 2 Sensor 1. That would be the left bank upstream sensor. Make sure you check the PCV vacuum hose assembly very carefully and the other vacuum connections as well. The stalling may be due to a dirty throttle. A faulty MAF will generally tend to set codes for both banks.
  3. +1 on above. Start looking first for a vacuum leak at a location which would affect bank 2 more than bank 1 (driver's side left).

    Next look for an exhaust leak on bank 2.

    Look for leaks before resorting to blindly replacing the O2 sensors. The O2 sensor itself may be bad but the odds don't favor it as being the cause.

    P1151 - Lack of HO2S-21 Switch, Sensor Indicates Lean

    • Electrical:
      • Short to VPWR in harness or HO2S
      • Water in harness connector
      • Open/Shorted HO2S circuit
      • Corrosion or poor mating terminals and wiring
      • Damaged HO2S
      • Damaged PCM
    • Fuel System:
      • Excessive fuel pressure
      • Leaking/contaminated fuel injectors
      • Leaking fuel pressure regulator
      • Low fuel pressure or running out of fuel
      • Vapor recovery system
    • Induction System:
      • Air leaks after the MAF
      • Vacuum Leaks
      • PCV system
      • Improperly seated engine oil dipstick
    • EGR System:
      • Leaking gasket
      • Stuck EGR valve
      • Leaking diaphragm or EVR
    • Base Engine:
      • Oil overfill
      • Cam timing
      • Cylinder compression
      • Exhaust leaks before or near the HO2S(s)
    kramer likes this.