My 94 Ranger, 3.0 gets a check engine light often. I read the code and the ECM provides a code number of 539 which I my book says"Air conditioning on during self test". The thing is there are no performance issues with the truck and the AC works fine, just a nagging check engine light comes on after about 15 minutes of driving. Anyone seen this before or have some ideas what the problem might be? Thanks.
Most likely a minor situation. My air bag warning light kept blinking, until a friend mentioned that seat belt slack sometimes made an for an error code. I adjusted the seat belts, disconnected the battery for 5 minutes and the warning light has been off since. Good luck.
I think you have a EEC-IV system. Sounds like you have only done the KOER test (Key On, Engine Running). If you do the KOEO test (Key On, Engine Off), it'll tell you what the stored codes are. I'm going to guess it's EGR related.
As to the reason you got that 539, it sounds like you simply didn't turn off the AC while running the KOER test.
CJB
most likely an 0.2 scensor..
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