air fuel mixture

[pwpanas]

Originally Posted by kidsusukigsxr

...can anyone tell me about the emissions control system diagnotic code 25 air-fuel raio rich malfunction. I don't know which sensor i need to change...

1. Diagnostic code 25 is "Air-Fuel Ratio Lean Malfunction" (i.e. not "rich" - that'd be code #26)
2. Possible areas of concern are as follows (listed roughly in decreasing order of likelihood):

• • Main oxygen sensor (a likely cause)
  • Air/vacuum/boost leak (also a strong possibility)
  • Water temp sensor (sensor corroded, due to infrequent coolant flushes)
  • Ignition system (old spark plugs (copper?))
  • Air flow meter (dirty/oily (from k&n oil?))
  • Fuel line pressure (eg. bad fuel pump)
  • Injector (dirty)
  • Open or short in main oxygen sensor circuit
  • Open or short in Injection circuit
  • ECU

Of course, other members of the forum please feel free to correct, re-order, or add to this list.


kidsusukigsxr, please answer the following questions:

• What year is your Supra? ...and is it turbo or n/a?
• What modifications were done to it?